TC-3883
TECHNICAL SUPPORT DOCUMENT
FOR REGULATING DILUTION AND
DEPOSITION OF DRILLING MUDS
ON THE
OUTER CONTINENTAL SHELF
NOVEMBER, 1984
FOR:
EPA REGION X
SEATTLE, WASHINGTON
AND
JONES AND STOKES ASSOCIATES
BELLEVUE, WASHINGTON
F
i
&
i
-------
TC-3883 - Final Report
TECHNICAL SUPPORT DOCUMENT FOR REGULATING
DILUTION AND DEPOSITION OF DRILLING MUDS
ON THE OUTER CONTINENTAL SHELF
Prepared by:
Gary Bigham
Lys Hornsby
Gary Wiens
Tetra Tech, Inc.
11820 Northup Way, Suite 100
Bellevue, WA 98005
for
EPA Region X
Seattle, WA
and
Jones and Stokes Associates
Bellevue, WA
November, 1984
-------
CONTENTS
Page
LIST OF FIGURES iv
LIST OF TABLES vl
ACKNOWLEDGEMENT vii
I. INTRODUCTION 1
II. DRILLING MUD DILUTION 3
FIELD STUDIES 3
OFFSHORE OPERATORS COMMITTEE MODEL 5
Model Description 5
Model Results 13
Summary 26
Sensitivity Analysis 30
EPA MODEL DESCRIPTION 31
III. SOLIDS DEPOSITION 33
FIELD STUDIES 33
OOC MODEL RESULTS 35
Summary 41
IV. FACTORS TO CONSIDER IN EVALUATING DISCHARGE LIMITATIONS 42
MUD COMPOSITION 42
Marine Water Quality Criteria 47
TOXICITY OF DRILLING MUDS 49
BOTTOM DEPOSITION 52
SUMMARY OF OOC MODEL RESULTS 54
EPA MODEL RESULTS 54
EFFECTS OF ICE COVER ON DRILLING MUD DILUTION 54
-------
V. RECOMMENDATIONS 61
RECOMMENDED DISCHARGE REGULATIONS 61
OOC MODEL SIMULATIONS 63
FIELD STUDIES 63
REFERENCES 65
APPENDIX A - MINIMUM DILUTIONS AS PREDICTED BY THE OOC MODEL
APPENDIX B - SOLIDS DEPOSITION AS PREDICTED BY THE OOC MODEL
APPENDIX C - FIELD OBSERVATIONS OF DRILLING MUD DILUTION
APPENDIX D - FIELD OBSERVATIONS OF SOLIDS DEPOSITION
m
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FIGURES
Number Page
1 Idealized jet discharge described by OOC model 6
2 Minimum solids dilution versus distance from the discharge for
different water depths 15
3 Minimum dissolved fraction dilution versus distance from the
discharge for different water depths 16
4 Minimum solids dilution versus distance from the discharge for
different discharge rates 18
5 Minimum solids dilution versus distance from the discharge for
different current velocities 19
6 Minimum dissolved fraction dilutions versus distance from the
discharge for different current velocities 20
7 Minimum solids dilutions versus travel time for different
current velocities 21
8 Minimum solids dilutions versus distance from the discharge
for different degrees of density stratification 23
9 Minimum solids dilution versus distance from the discharge for
predilution and no predilution at 40 m 24
10 Minimum dissolved fraction dilution versus distance from the
discharge for predilution and no predilution at 10 m 25
11 Minimum solids dilution versus distance from the discharge for
different bulk mud density discharges at 10 m 27
12 Maximum suspended solids concentration versus distance from
the discharge for different bulk mud density discharges
at 10 m 28
13 Cumulative percent of deposited solids versus distance from
the source for different water depths 36
14 Cumulative percent of deposited solids versus distance from
the source for different current velocities 38
15 Cumulative percent of deposited solids versus distance from
the source for different discharge rates 39
16 Cumulative percent of deposited solids versus distance from
the source for different bulk mud densities 40
IV
-------
17 Depth-averaged solids dilution at 100 meters from discharge
predicted by the EPA model for 10 cm/sec current speed 56
18 Depth-averaged solids dilution at 100 meters from discharge
predicted by the EPA model for 2 cm/sec current speed 57
19 The relationship between ice cover, current velocity, and
time of year 60
-------
TABLES
Number
1 Suspended solids dilution characteristics of various drilling
sites 4
2 Summary of OOC model inputs 7
3 Example spot profile results at 1,000 and 2,000 sec after start
of discharge (from OOC model) 9
4 Example of summary table of mass distribution of solids (from
OOC model) 10
5 Example plan view of combined solids on the bottom at 5,000 sec
after start of discharge (from the OOC model) 11
6 Summary of OOC model inputs for test cases 14
7 Summary of results of deposition studies 34
8 Approved drilling mud types 43
9 Maximum trace metal concentrations measured in drilling mud
discharges 45
10 Soluble and solids metal concentrations in dredged materials
dumped at sea, 1978 and 1979 46
11 Trace metal concentrations of the whole mud and dissolved
fraction and federal marine water quality standards 48
12 Summary of major field investigations of the environmental
fate and effects of drilling fluids and cuttings discharged
to the environment 53
13 Summary of minimum solids dilutions predicted by the OOC Model
at 100 m (328 ft) from the discharge 55
14 Comparison of depth-averaged solids dilutions at 100 m (328 ft)
from the discharge for the OOC and EPA models 58
VI
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ACKNOWLEDGEMENT
We wish to acknowledge the contribution of the people who assisted
in the preparation of this report. Dr. Harvey Van Veldhuizen of Jones
and Stokes Associates prepared the description of drilling mud toxicity.
U.S. Environmental Protection Agency (EPA) Region X personnel who contributed
to the report include Mr. Duane Kama, Ms. Marcia Lagerloef, Ms. Jan Hastings,
Mr. Thomas Denning, and Ms. Kerrie Schurr, who aided in data collection
and offered many helpful suggestions. We wish to thank Mr. John Yearsley
of EPA Region X for providing a description and the computer code for the
EPA drilling mud dilution model used in this report and for assistance
with model operation.
vn
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I. INTRODUCTION
The potential impacts to the marine environment from drilling mud
discharges from exploratory drilling activities on the outer continental
shelf have been the subject of recent research and debate. In the past
there has been little scientific consensus regarding the physical fate
and biological effects of drilling discharges. This lack of consensus
has led to problems for regulatory agencies involved in permitting drilling
discharges. The overall objective of this report is to evaluate discharge
limitations needed to ensure compliance with state and federal water quality
standards and criteria.
Ocean Discharge Criteria Evaluations (ODCE) have been completed as
part of EPA's general NPDES permitting procedure for exploratory oil drilling
activity at several areas on the Alaskan Outer Continental Shelf. The
evaluation procedure included analysis of the fate of discharged drilling
muds. This analysis included review of mud dispersion field studies and
computer simulations of mud discharges using the Offshore Operators Committee
(OOC) model and EPA's model. The purpose of this report is to assemble
the results of field studies and OOC model runs to describe how the dispersion
and bottom deposition of discharged drilling mud is influenced by different
variables such as water depth, discharge rate, current velocity, density
stratification, predilution, and initial suspended solids concentration
(mud bulk density). With this information as background, alternative means
of regulating drilling mud discharges from both exploratory, and development
and production operations to assure compliance with water quality criteria
are presented.
The second part of this report presents field observations and OOC
model simulations of drilling mud dilution. Brief descriptions of the
OOC and EPA model formulations and limitations are also presented. Solids
deposition results from field studies and the OOC model are discussed in
1
-------
the third section. The fourth section discusses the factors considered
in determining discharge limitations. Recommendations for discharge regula-
tions and future OOC model runs, and important characteristics of a sample
drilling mud discharge monitoring study are summarized in the fifth section.
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II. DRILLING MUD DILUTION
FIELD STUDIES
Several field studies have been conducted to measure dilution and
dispersion of drilling muds under various oceanographic conditions. Table 1
summarizes the important variables measured in these studies and suspended
solids dilution for various drilling sites. There are several problems
in gathering and interpreting field data, and calculating associated dilutions.
Important field studies and associated problems are discussed in detail
in Appendix C. Problems with existing field data include poor study design,
difficulty in locating and sampling the plume, small discharge volumes
studied, and results that do not represent expected plume behavior.
It is difficult to directly compare the results of different field
studies due to varying sampling techniques, frequency and location, oceano-
graphic conditions, and discharge characteristics. However, general conclusions
supported by the results of these field studies include:
t Drilling muds (particulate) are generally diluted by factors
greater than 2,000:1 at 100 m (328 ft) from the discharge
site.
Suspended solids dilutions generally increase as depth or
distance from the discharge increases.
The minimum dissolved fraction dilution of 112:1 occurred
in shallow water at 61 m from the source. Dissolved fraction
dilutions should be less than or equal to particulate dilutions
due to settling of solids from the effluent plume.
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TABLE 1. SUSPENDED SOLIDS DILUTION CHARACTERISTICS
OF VARIOUS DRILLING SITES
Location
Tanner Bank
Gulf of Mexico
Mid-Atlantic
Norton Sound
Lower Cook Inlet3
Tern Island
(Beaufort Sea)
Reindeer Island
(Beaufort Sea)
Reference
Ecomar (1978)
Ray and Meek (1980)
Ayers et al . (1980a)
Ayers et al . (19806)
Ecomar (1983)
Houghton et al . (1980)
Northern Technical
Services (1983)
Northern Technical
Services (1981)
Current
(cm/sec)
11.8-45.2
0-20 (min-max)
21-27
15-77
31-98 (min-max)
78-121
122-144
11-12 (near
bottom avg. )
4.5
4.4 (near
bottom avg.)
Depth
(m)
63
23
120
12-13
62
62
62
6.7
8.4
5.5
Flow
(bbl/h)
10-754
275-1,000
275
500
1,065
180
1,200
20
84
34
1,510
21
Distance from
Discharge (m)
3
100
100
500
97
192
119
193
100
940
1,980
830
1,760
100
200
100
160
61
61
Suspended Solids
Dilution
500-1,000:1
10,000-400,000
2,000-40,000:1
200,000:1
80,000:1
110,000:1
60,000:1
70,000:1
10,000:1
46,000:1
119,000:1
22,000:1
107,000:1
38,000:1
104,000:1
5,000:1°
24, 000: 1C
112a
500,000a»e
Initial
Suspended Solids
Concentration (mg/1 )
250,000
1,430,000
277,400
250,400
302,000
103,000
700,000
20,000
250,000
696,000d
630,000d
8 These dilutions are for a dye tracer, not suspended solids.
b Predilution of 30:1 with seawater.
c Predilution of 75:1 with seawater. Background levels may have been reached at 100 m (328.1 ft).
d A water content of 40 percent was assumed. Bulk mud density was 10.6 Ib/gal.
e The effluent was probably not measured and therefore a large dilution was obtained.
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OFFSHORE OPERATORS COMMITTEE MODEL
Model Description
A complete description of model formulations, concepts, required inputs,
output options, and model limitations is given in the user's manual by
Brandsma et al . (1983, pp. 5-1 - 5-2), however, important details of the
formulation will be reviewed here. The OOC model was developed to describe
the fate of offshore drilling mud discharges. The model simulates the
effluent plume (commonly known as the lower plume) through three phases:
the jet phase (convective descent), dynamic collapse, and passive diffusion
as shown in Figure 1. The model also simulates an upper plume, which appears
to form when particles of mud separate from the main plume during the convective
descent phase. The upper plume may represent up to 10 percent of the discharged
mud. For the runs presented here, 10 percent of the discharged mud was
separated by the model (referred to as forced separation) in a linear fashio-n
over the depth of the convective descent.
Inputs to the model include data from four categories: drilling mud
characteristics, discharge conditions, ambient characteristics and model
options. These inputs are summarized in Table 2. Drilling mud characteristics
consist of.mud bulk density, discrete particle classes, concentration,
density, and settling velocity for each particle class. Discharge conditions
of interest include discharge rate, duration, orientation of the discharge,
and rig type and position. Density profile, current velocity and distribution,
and wave height and period are important ambient conditions. Model options
include input options and output format control. Input conditions used
in this report assume that the drilling rig is a jackup with a submerged
discharge pipe. The concentration of suspended solids in the drilling
mud is 1,441,000 mg/1 unless stated otherwise. All model runs assume a
density gradient of less than approximately lxlO~4 g/cm3 per meter depth
(increasing with depth). The model currently does not accurately simulate
discharges from a gravel island. The current velocity profiles used are
uniform distributions (over the depth) with a sharp decrease in velocity
near the seafloor. Model runs represent somewhat artificial conditions
because of the representation of current speed and direction. For purposes
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CROSS SECTION
CROSS SECTION
CLOUD CROSS SECTION
PASSIVE DIFFUSION
ENCOUNTER
NhUlHAL
BUOYANCY
DIFFUSIVE SPREADING
GRFATF.RIHAN
DYNAMIC SPREADING
INFERENCE.: Brandsma and Sauer, 1983.
Figure 1. Idealized jet discharge described by OOC model.
-------
TABLE 2. SUMMARY OF OOC MODEL INPUTS
Category
Variable
Typical Value3
Discharge Conditions
Drilling Mud Characteristics
Receiving Water Characteristics
Rate
Duration
Angle (from horizontal)
Depth
Nozzle radius
Rig type
Rig length
Rig width
Forced separation of fine particles
Bulk density
Initial solids concentration
Tracer concentration
Current velocity
Wave height
Wave period
Density gradient (Aot/m depth)
100-1,000 bbl/h
1,800-3,600 sec
90°
0.3 m (1.0 ft)
0.1 m (0.33 ft)
Jackup
70.1 m (230 ft)
61.0 m (200 ft)
yes
2.09 g/cm3 (17.4 Ib/gal)
1,441,000 mg/1
100 mg/1
2-30 cm/sec ( 0.066-0.984 ft/sec)
0.61 m (2 ft)
12 sec
<0.10
3 Typical values used for all model runs unless otherwise specified.
-------
of the model simulation, ocean currents were specified at a constant direction
and a constant speed for the entire simulation. In reality, current speed
and direction are quite variable. As a result, predicted dilution may
be conservatively low while predicted solids accumulation rates are conserva-
tively high. Also, the bottom area receiving deposits is under-predicted.
Typical drilling rig and discharge characteristics used include a rig length
of 70 m (230 ft), a rig width of 61 m (200 ft), a discharge nozzle radius
of 10.2 cm (4 in), a vertical angle of discharge (90°) and a 0.3 m (1.0 ft)
discharge depth (below the surface).
Outputs from the model include concentrations of particulate and dissolved
mud components at various time steps shown in tabular and graphical form.
Depth profiles of the concentrations of particulate and dissolved components
for given time steps (Table 3) enable the calculation of minimum or depth-
averaged dilution at selected points downstream of the source. A solids
mass distribution summary (Table 4) shows the weight of solids in each
plume phase, the amount of solids on the bottom, and the spatial deposition
pattern (Table 5).
It should be noted that the model has not been completely verified
with actual field data. Comparison of model results to field data for
a 275 bbl/h discharge in 23 m (76 ft) of water showed that the model "...repro-
duces several observed features of drill mud discharges" (Brandsma et al.,
1980, p. 598). No-field data sets are currently available to further verify
the model for the extreme range of water depths for which it has been run
here (5 m to 120 m). It can only be stated that the model results appear
to be reasonable and provide an estimate of the expected fate of discharged
drilling muds. Numerical values provided by the model should not be considered
to be of high precision. It is presently not possible to establish confidence
limits to model results.
Ecomar recently completed a new field study to collect data to verify
the OOC model. The study was designed to describe both particulate and
dissolved fraction water column concentrations and bottom accumulation
of solids. The discharge was located off Huntington Beach, California,
-------
TABLE 3. EXAMPLE SPOT PROFILE RESULTS AT 1,000 AND 2,000 SEC
AFTER START OF DISCHARGE (FROM OOC MODEL)
SPOl PROF ILES Or
DISTANCE
BEARING
X-COORO.
Z-COORO.
W. DEPTH
DEPIH
0.0
3. 3
6. 7
10.0
U.3
16.6
20.0
23.3
26.6
30.0
33.3
36.6
39.9
M3.3
M6.6
M9.9
53.3
56.6
59.9
63.3
66.6
69.9
73.2
76.6
79.9
1 00 . 0 200 . 0
2'lO.n 2MO.O
1050.0 1100.0
271 3. M 2626.8
80.0
0.00
(1.33
2.18
12.85
16.63
115. 85
192.18
216. 17
1 79.88
131.30
99. 12
85.66
99.00
118.05
228. H3
327.31
U23. 77
195.01
521.53
1195. 1 7
123.68
326.57
226.11
I'll . 17
79. 12
...MULTIPLY DISPLAYED
DISTANCE
Bf An 1 NG
X-COORO.
Z-COORO.
W. Of Pill
DEPTH
0.0
3.3
6.7
10.0
13.3
16.6
?0.0
23. 3
26.6
30.0
33. 3
36.6
39.9
13. 3
16.6
'19.9
53. 3
56.6
59.9
63. 3
66.6
69.9
73.2
76.6
79.9
100.0
2HO.O
1050.0 1
80.0
0.0
0.0
0.58
3.51
11.99
13. 72
8'.53
120.91
118. 11
85.25
HI. ?2
19.91
6.09
1.26
0.05
O.O
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
VALUES
SPOT
200.0
210.0
100.0
2713.1 2626.8
80.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
'1.0
o.o
0.0
0.0
0.0
o.o
0.0
0.0
0.0
0.0
0.0
o.o
0.0
0.0
0.0
0.0
0.0
6.17
.MULT IPLY DISPLAYED
80.0
O.OP
0.00
0.00
0.00
0.01
0.01
0. 30
1.20
3.12
5.29
5. T>
3.98
1.75
(1.19
0.07
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
VALUtS
100.0
260.0
1069.5
2106 . 1
80.0
0.0
O.o
0.0
0.0
0.0
0.0
0.0
0.0
0.0
o.o
o.o
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
o.o
BY 1 . 000
PROFILES Of
100 . 0
?60.0
1069.5
2106. 1
8O . I)
0.95
3.11
9.35
19. 10
29.27
33.52
28 . 61
18.16
10. 15
8.00
10.92
13. 79
12. 19
7. 18
2. 77
0. 70
0. M
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
BY 1 . 000
COMRINED
600 . 0
260.0
1 101.2
2209. 1
80.0
0.0
0.0
0.0
0.0
0.0
0.0
o.o
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
O.I)
0.0
0.0
0.0
0.0
0.0
0.0
o.o
0.0
0.0
COMOINCO
600.0
260.0
1 101.2
2209. 1
80.0
0.0
0.0
0.0
0.0
0.0
0.0
o.o
0. 1)
0.0
0.1)1
o. 10
O. 19
0.22
0. 16
0.08
0.03
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
SOI IDS CONCENTRATIONS
500.0
280.0
913.2
2307.6
80.0
0.0
0.0
O.n
O.I)
0.0
o.o
0.0
0.0
0.0
0.0
O.I)
0.0
o.o
0.0
0.0
o.o
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
700.0
280.0
878.5
21 10.6
80.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1 0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
SOLIDS CONCENTRATIONS
500.0
280.0
913.2
2307.6
80.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.31
12.09
11.37
70.93
18. 11
13.15
1.09
2.52
0. 15
0.01
O.O
0.0
0.0
700.0
280.0
8/8.5
2110.6
80.0
0.0
0.0
0.0
0.0
0.0
0.0
o.o
0.0
0.0
0.0
0.0
0.0
0.01
0.01
0.09
0. 12
0. 10
o.oi
o.oo
0.00
0.00
0.00
0.00
0.0
0.0
(MC/LITER
800.0
300.0
600.0
2107.2
80.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
o.o
0.0
0.0
0.0
0.0
0.0
0.0
o.o
0.0
0.0
0.0
0.0
0,0
0.0
0.0
0.0
0.0
(MC/LITER
800.0
300.0
600.0
2107.2
80.0
0.0
0.0
0.0
0.0
0.0
0.0
0,0
0.0
0.0
0.0
0.0
0.0
0.0
o.o
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
OF SAMPLE
1000.0
300.0
500.0
1931.0
80.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
OF SAMPLE
1000.0
300.0
500.0
1931.0
80.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
o.n
o.o
o.o
o.o
O.I)
o.o
o.o
o.o
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
) TIME(SrC) - 1000.0
1100.0
320.0
157.1
2092.9
80.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1300.0
320.0
1. 1
1961.1
80.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
o.o
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
) TIME(SEC) 2000.0
1 100.0
320.0
157.1
2092.9
80.0
0.0
0.0
0.0
0.0
0.0
0.0
o.o
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
o.o
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1300.0
320.0
1. 1
1961.1
80.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
o.o
0.0
0.0
0.0
0.0
0,0
0.0
o.o
0.0
0.0
0.0
0.0
0.0
Source: Brandsma et al. (1983).
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TABLE 4. EXAMPLE SUMMARY TABLE OF MASS DISTRIBUTION
OF SOLIDS (FROM OOC MODEL)
SUMMARY OF MASS DISTRIBUTION ( LBS)
CLASS NAME
SOLI
SOL2
SOL3
SOLU
SOLS
SOL6
TOTL
SOL DENS C/CC 3.9590 3.9590 3.9590 3.9590 3.9590 3.9590
CONC VOL FRAC 0.036UO 0.036UO O.OU368 0.07280 0.13830 0.036UO
SET VELO FT/S 0.021600 0.006820 0.002780 0.0011430 0.000758 O.OOOU27
TOTAL LBS 12639. 12639. 15167. 25278. U6021.
12639. 126382.
TIME(SEC) = 1000.0
TO BE OISCHG.. 0.
IN OVN PLUME.. 132U.
IN PASS DlFF.. 219.
ON BOTTOM 11096.
0. 0.
3U10. 5101.
19141. 5068.
7289. 5001.
0.
8953.
10492.
5835.
0.
16836.
26066.
5120.
0. 0.
1873. 37U97.
10572. 5U358.
195. 3U536.
TIME(SEC) =
TO BE OISCHC.
IN DVN PLUME.
IN PASS DIFF.
ON BOTTOM
2000.0
0.
0.
UU.
12593.
0.
0.
1691.
109H7.
0.
0.
3399.
11767.
0.
0.
5U03.
19873.
0.
0.
20521.
271498.
0.
0.
12278.
363.
0.
0.
U3336.
83040.
TIME(SEC) =
TO BE DISCHC.
IN DYN PLUME.
IN PASS DIFF.
ON BOTTOM
3000.0
0.
0.
2.
1263U.
0.
0.
1008.
11628.
0.
0.
21425.
12739.
0.
0.
3305.
21969.
0.
0.
13173.
3U8UU.
0.
0.
12217.
U23.
0.
0.
32129.
9U238.
TIME(SEC) =
TO BE DISCHG.
IN DYN PLUME.
IN PASS DIFF.
ON BOTTOM....
5000.0
0.
0.
0.
12635.
0. 0. 0. 0. 0. 0.
0. 0. 0. 0. 0. 0.
151. 1372. 2075. 102141. 12085. 2592U.
12U81. 13789. 2319U. 37772. 555. 100U25.
NOTE: COMPARISON OF VALUES IN TABLE WITH THOSE
DUE TO COMPUTER ROUND-OFF ERROR.
IN THE PLANVIEVS MAY NOT BE EXACT
Source: Brandsma et al. (1983).
10
-------
TABLE 5. EXAMPLE PLAN VIEW OF COMBINED SOLIDS ON THE BOTTOM AT 5,000 SEC
AFTER START OF DISCHARGE (FROM THE OOC MODEL)
IOIAI ACCIIHIIIAltD SOLID MASS (IDS/OHIO SQII) ON BOIIOM FIML(SIC) = 5000.0
RIG I OCA I I ON: M - 1000.0 M, N - i'BOO.O II OHIO STAC I HP, - 100.0 (f
. . .Mill 1 II'LY OISPI AYt I) VAI Ul S IIY 100.11 (IICINII... ' - .11. .01 11^ .11. .01101)
M N= 1 2 3 ll r. 6 / 8 9 III II IP 13 11 lr. 16 17 18 19 ?0 21 ?? P3 21* 25 26 27 28 29 30
1 OOOO 00000000000000000000000000
? 0 0 0 O II O 0 (I 0 0 0 0 0 0 O 0 0 0 0 0 0 0 0 n 0 0 0 0 0 0
3 0 O O O II 0 II O O 0 0 II O 0 O II 0 0 O O 0 O O O 0 0 0 0 0 0
M 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 4 * 0 0 0 (I 0 0 0 0 0 0
5 0 0 0 O II O O 0 0 0 I) 0 O 0 0 0 0 4 .09 .02 .02 4 0 0 0 0 0 0 0 0
6 0 0 O 0 !> (I II 0 O 0 O II 0 0 O O 0 4 .01 .I'l .211 .33 .61 .05 000000
7 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 + .01 .35 3.'» 8. 1 5.9 1.8 . 12 0 0 0 0
8 0 0 0 0 0 0 0 0 0 0 0 0 II 0 0 n (I 0 0 4.031.111060392.5.25.01 0 0
Q I) 0 0 0 0 U 0 II 0 0 0 I) 0 II 0 O 0 0 0 I) O.I01.65.72HI 222 7. 7 .20 + 0
^ RIG LOCATION
10 0 000000 OOOOOOOOOOOOOOOO .03 .50 1.8 197 [209J 4 0
II 0 0 0 O 0 0 0 II 0 0 0 0 (1 II 0 0 0 0 0 0 0 0 0 0 0.05.57.05 + 0
12 OOOOOOOOIIOOOUOOOOOOOOOOOOOOOOO
1J QOOOOOOOOOOOOO OOOOOOOOOOOOOOOO
|l| o O 0 O II 0 0 0 (I 0 0 0 0 O II 0 0 O 0 0 0 0 II 0 0 0 0 0 0 0
)«, i) || o 0 II II O II 0 O 0 O II 0 II 0 O 0 0 0 0 0 0 0 0 0 0 0 O 0
16 000000000000000000000000000000
H ooOOOOOOOOOOOOOOOOOOOOOOOOOOOO
10 () () o o I) o o o o 0 0 II 0 I) 0 0 0 I) 0 0 0 0 0 0 0 0 0 0 0 0
Source: Brandsma et al. (1983).
-------
at a water depth of 18.3 m (60 ft). A report is expected at the end of
the year (Sauer, T., 4 April 1984, personal communication).
The model has considerable flexibility in simulating the many processes
that affect dilution and deposition of drilling mud discharges; however,
the model has certain limitations including (Brandsma et al. 1983, p. 5-2):
The model does not account for the effects of flocculation
of mud solids in the water column. It is assumed that the
settling velocity distribution entered into the program
by the user reflects the flocculated state of the solids.
t The algorithm used in the model to simulate the forced separation
of fine material near the discharge source (during the jet
phase) has no theoretical basis. It was developed to simulate
field and laboratory observations.
t Results of wake intensity studies are used in the model
formulation to describe the effects of a turbulent wake
on the discharge plume. However, the relationship of rig
structure and ambient velocities to wake intensity is not
yet completely understood. The model accounts for the wake
effect by using random fluctuations of the position, and
size increases of effluent "clouds" when the "clouds" are
within the wake zone. The size of the wake zone is determined
by the rig structure and the ambient velocities.
The model cannot simulate the situation where the plume
descends vertically and encounters the bottom (shallow,
low velocity waters). As ambient current velocities are
reduced, the plume trajectory becomes nearly vertical and
difficulties in producing a stable simulation arise. Increasing
. the ambient current speeds slightly or changing the angle
of the pipe from vertical will help to produce a stable
simulation.
12
-------
In addition, the model does not account for solids resuspension or biological
uptake.
The real value of the OOC model is its potential for use as a comparative
tool. The effects of changes in the various input parameters may be assessed
to determine which variables are the most important. This has been the
focus of this modeling effort.
Model Results
For this report, the OOC model was run for 20 test cases with inputs
as summarized in Table 6. These cases cover a variety of conditions including
variation in water depth, discharge rate, current velocity, density stratifi-
cation, predilution, and mud bulk density (initial solids concentration).
Tabulated model results (minimum dilutions with distance from the source)
for these test cases are provided in Appendix A.
Minimum dilution and distance from the discharge from representative
test cases were plotted to determine relationships between dilution and
discharge rate, current velocity, water depth, density stratification,
predilution and mud bulk density. To determine the effect of water depth
on initial dilution, the results of cases 3, 5, 6, 11, 13, 15, and 16 [water
depths ranging from 5 to 120 m (16 to 394 ft)] were compared. For demon-
stration, Figure 2 shows the minimum solids dilution with distance from
the discharge and Figure 3 shows the minimum dissolved fraction dilution
with distance from the discharge for representative cases 3, 5, 13, and 15.
These data indicate that the minimum solids dilution at distances greater
than 80 m (262 ft) from the discharge is generally greater for the shallow
water case (minimum solids dilution increases as water depth decreases).
Within 80 m (262 ft) of the discharge source, this relationship is reversed;
minimum solids dilution increases as water depth increases.
Another interesting observation is the slope of these dilution curves
(Figure 2). Minimum solids dilutions for shallow water cases increase
much more rapidly than deeper water cases. As water depth increases, the
minimum solids dilution curve becomes more level. These results indicate
13
-------
TABLE 6. SUMMARY OF OOC MODEL INPUTS FOR TEST CASES*
Density
Stratification,
Case
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Water
Depth
(m)
40
40
40
40
5
10
10
10
10
15
15
15
20
40
70
120
120
. 5
15
15
Discharge
Rate
(bbl/h)
1,000
1,000
1,000
100
1,000
1,000
1,000
100
1,000
1,000
1,000
1,000
1,000
1,000
1,000
1,000
1,000
250
250
250
Surface
Current
(cm/sec)b
2
10
10
10
10
10
10
10
10
2
10
30
10
10
10
10
32
10
2
10
(Bottom to
Surface)
3.9
3.9
3.9
3.9
0.1
0.7
0.7
0.7
0.7
1.07
1.07
1.07
1.00
0.5
2.5
0.98
1.30
0.1
1.07
1.07
Other
Predilution 9:lc
Predilution 9:lc
Predilution 9:lc
Mud bulk density = 9 Ib/gal
Minimum stratification (40
_
a All cases use a 2.09 g/cm3 (17.4 Ib/gal) mud unless otherwise specified (initial sol
concentration 1,441,000 mg/1).
b Uniform velocity distribution with depth was assumed, with a sharp decrease in veloc
near the bottom.
c Nine parts.water with 1 part mud.
14
-------
100,000
10,000 -
o
t-
CO
Q
_i
O
CO
1,000 -
100
TEST CONDITIONS
DEPTH(m) SYMBOL
20
40
70
ALL. CASES USE A DISCHARGE RATE OF
lOOObDl'h AND A CURRENT VELOCITY
OF 10cnvsec
100 200
DISTANCE FROM DISCHARGE (m)
300
Figure 2. Minimum solids dilution versus distance from the
discharge for different water depths.
15
-------
100,000
o
10,000
Q
Q
LU
Z
O
en
c/2
Q
1,000
TEST CONDITIONS
CASE
5
13
3
15
DEPTH(m)
5
20
40
70
SYMBOL
u
100
ALL CASES USE A DISCHARGE RATE OF
1000bbl/h AND A CURRENT VELOCITY
OF 10cm/sec.
I
100 200
DISTANCE FROM DISCHARGE (m)
300
Figure 3. Minimum dissolved fraction dilution versus distance
from the discharge for different water depths.
16
-------
that rapid settling of solids out of the water column causing increased
dilutions is the dominant process influencing solids dilution in shallow
waters.
The minimum dissolved fraction dilutions, on the other hand, exhibit
a very straightforward relationship to water depth (Figure 3). As water
depth increases, dissolved fraction dilutions increase for all distances
from the source. As water depth increases, the corresponding increase
in water volume determines the dissolved fraction dilution.
A relationship between minimum dilutions and drilling effluent discharge
rate may be determined by comparing the results of cases 3 and 4, and 6
and 8. Figure 4 shows this relationship for the minimum solids dilution
for cases 3 and 4. These data indicate that as discharge rate increases,
the minimum solids dilution decreases. The minimum dissolved fraction
dilutions exhibit the same relationship. A similar result is found for
cases 6 and 8.
Cases 1 and 2; and 10, 11, and 12 were compared to describe the relation-
ship between initial dilution and current velocity. Figure 5 shows this
relationship for solids dilution and Figure 6 presents the results for
the dissolved fraction dilutions for representative cases 10, 11, and 12.
As indicated by Figure 5, minimum solids dilution achieved at a given distance
from the source decreases as current velocity increases. A similar, but not
as clear, relationship holds for the dissolved fraction dilutions (Figure 6).
Case 10, with the lowest current velocity, shows higher dissolved fraction
dilutions at most distances. However, case 11 (10 cm/sec current) and
12 (30 cm/sec current) show similar dissolved fraction dilutions even though
the current velocities are significantly different. A reason for these
results is that a drilling effluent plume in a higher current environment
takes less time to travel a specific distance, therefore allowing less
time for dispersion to occur. To determine the b.ehavior of drilling effluent
plumes in high velocity environments, travel time should be considered.
Figure 7 shows the relationship between travel time and minimum solids
dilution. These results indicate that for a given travel time, solids
dilutions are higher for the higher velocity cases. Therefore, in receiving
17
-------
100,000
10,000
(f)
Q
_i
o
en
1,000
TEST CONDITIONS
CASE DISCHARGE RATE (bbl/h) SYMBOL
BOTH CASES USE A WATER DEPTH OF 40m
AND A CURRENT VELOCITY OF lOcm/sec.
100
I
100 200
DISTANCE FROM DISCHARGE (m)
300
Figure 4. Minimum solids dilution versus distance from the
discharge for different discharge rates.
18
-------
100,000
10,000
C/)
Q
_i
O
C/D
1,000
TEST CONDITIONS
CASE VELOCITY (cm/sec)
10 2
11 10
12 30
SYMBOL
100
ALL CASES USE A DISCHARGE RATE OF
1000 DDi/h AND A WATER DEPTH OF 15m
I
100 200 300
DISTANCE FROM DISCHARGE (m)
Figure 5. Minimum solids dilution versus distance from the
discharge for different current velocities.
19
-------
100,000
d 10,000
Q
Q
LJJ
c/5
Q
1,000
TEST CONDITIONS
CASE VELOCITY (cm/sec) SYMBOL
11 10 ....i....
12 30
ALL CASES USE A DISCHARGE RATE OF
I000bbl/h AND A WATER DEPTH OF 15m
100
I
100 200
DISTANCE FROM DISCHARGE (m)
300
Figure 6. Minimum dissolved fraction dilutions versus
distance from the discharge for different
current velocities.
20
-------
100,000
10,000
CO
Q
_l
o
CO
1,000
100
r
u
CASE VELOCITY (cm/sec) SYMBOL
11 10
12 30
ALL CASES USE A DISCHARGE RATE OF
1000 Dbl/h AND A WATER DEPTH OF 15m
I
I
I
I
I
1000
2000
3000
4000
5000
6000
7000
TRAVEL TIME (sec)
Figure 7. Minimum solids dilutions versus travel time for
different current velocities.
21
-------
waters with high current velocities, the effluent is more rapidly mixed
over a larger area than in low velocity environments.
To determine the effects of density stratification (linear distribution
with depth) on minimum drilling mud dilutions, results of cases 3 and 14
were plotted in Figure 8. Case 3 has approximately eight times the _ ;t
of case 14, however, both minimum solids and dissolved fraction dilutions
are similar for the two cases. Therefore, density stratification of the
magnitude considered in these test cases does not significantly influence
drilling mud dilution. It should be noted that a sharp increase in density
(due to a thermocline or pycnocline) with depth could trap the effluent
plume higher in the water column, limiting solids settling and dissolved
fraction dilution. The exact position (depth) of this inflection would
be very important in determining the magnitude of the dilutions achieved
under these conditions.
Predilution of drilling mud is another factor that can influence the
final concentration of suspended solids in the water column following initial
dilution. Predilution is defined as the process of mixing drilling mud
and water to dilute the mud prior to discharge. In a case where .predilution
is used, the total dilution observed at some distance from the discharge
is a combination of dilution by the receiving water and predilution. Figure
9 shows the relationship between minimum solids dilution and predilution
for cases 2 and 4. These two cases [40 m (131 ft) depth] give roughly
identical total solids and dissolved fraction dilutions with distance.
These results [40 m (131 ft)] indicate that discharging 100 bbl/h of mud
prediluted with 9 parts of water (total discharge rate of 1,000 bbl/h)
is the same as discharging 100 bbl/h of straight drilling mud with respect
to dilution. A similar relationship was observed for solids dilutions
in 10 m (33 ft) of water (cases 7 and 8). Total solids dilutions were
identical for these two cases but the dissolved fraction dilutions for
case 8 (no predilution) were consistently higher (approximately 50 percent
higher) than case 7 (predilution) (Figure 10). These results indicate
that predilution or lowering the discharge rate by the appropriate amount
results in roughly identical solids dilutions with distance from the discharge
for waters 10 to 40 m (33 to 131 ft) deep. The relationship holds for
22
-------
100,000
10,000
cn
Q
_J
O
en
1,000
TEST CONDITIONS
CASE AOt(BOTTOM TO SURFACE) SYMBOL
3 3.9
100
BOTH CASES USE A WATER DEPTH OF
40m A DISCHARGE RATE OF 1000 bbl/h
AND A CURRENT VELOCITY OF 10 cm/sec
I
100 200
DISTANCE FROM DISCHARGE (m)
300
Figure 8. Minimum solids dilution versus distance from the
discharge for different degrees of density strati
fication.
23
-------
100,000
10,000
Q
Q
_i
o
1,000
100
TEST CONDITIONS
I
CASE TOTAL DISCHARGE RATE SYMBOL
(bbl/h)
2 1000 (PREDILUTION 9'1)
4 100
BOTH CASES USE A WATER DEPTH OF 40m
AND A CURRENT VELOCITY OF I0cm/sec
I
100 20O
DISTANCE FROM DISCHARGE (m)
300
Figure 9. Minimum solids dilution versus distance from the
discharge for predilution and no predilution at 40m
-------
100.000
10.000
g
£
£T
LL
Q
LLJ
O
CO
CO
o
1.000
100
: I
- I
-1
TEST CONDITIONS
CASE TOTAL DISCHARGE RATE SYMBOL
(bbl/h)
7 1000 (PREDILUTION 9 1)
8 100
BOTH CASES USE A WATER DEPTH OF 10m
AND A CURRENT VELOCITY OF 10cm/sec
I
100 200
DISTANCE FROM DISCHARGE (m)
300
Figure 10. Minimum dissolved fraction dilution versus dis-
tance from the discharge for predilution and no
predilution at 10m.
25
-------
dissolved fraction dilutions for the deeper [40 m (131 ft)J case. No data
on predilution are available for waters less than 10 m (33 ft) deep. However,
similar relationships are expected to apply to these cases.
The initial solids concentration of the mud greatly influences the
final solids concentration in the water column and the magnitude of dilution
achieved by the receiving water. Results of cases 6 and 9 were compared
to determine the relationship between mud bulk density (initial solids
concentration) and dilution (similar to predilution). For case 9, a mud
bulk density of 9 Ib/gal was represented by assuming the same solids density
and particle size distribution (fall velocity) as the 17.4 Ib/gal mud but
using a lower initial concentration of solids in the mud. Figure 11 shows
the minimum solids dilution with distance from the discharge for these
two cases. Higher solids and dissolved fraction dilutions are achieved
for case 6 (higher mud bulk density of 17.4 Ib/gal). However, lower water
column concentrations of suspended solids (Figure 12) are achieved in the
lower mud bulk density case (case 9). These results indicate that the
concentration of suspended solids in the receiving water is a result of
both the dilution and the initial solids concentration of the mud. A less
concentrated discharge (case 9) is not diluted by the receiving water as
rapidly as a concentrated discharge (case 6) but the less concentrated
discharge results in lower final receiving water solids concentrations.
Summary
The effects of various factors such as water depth, discharge rate,
current velocity, density stratification, and initial mud solids concentration
on particulate and dissolved fraction dilutions of drilling muds may be
described by comparing the results of the 17 test cases (OOC model) described
above. Results of these model runs support the following conclusions:
Within 80 m (262 ft) of the discharge and with a 10 cm/sec
current, particulate dilution increases as water depth in-
creases. However, at distances greater than approximately
80 m (262 ft), particulate dilution decreases as water depth
26
-------
100.000
10.000
2
o
cn
Q
1.000
100
TEST CONDITIONS
CASE BULK DENSITY INITIAL SOLIDS SYMBOL
(Ib/gal) CONCENTRATION (mg/l)
6 17.4 1.441,000
9 9 106.900
BOTH CASES USE A DISCHARGE RATE OF 1000bbl/h
AND A CURRENT VELOCITY OF 10cm/sec.
I
100 200
DISTANCE FROM DISCHARGE (m)
JOO
Figure 11. Minimum solids dilution versus distance from the
discharge for different bulk mud density dis-
charges at 10m.
27
-------
10,000
CT
E
<
cr
LU
o
z
o
o
co
Q
_i
o
CO
Q
LU
Q
Z
LU
CL
CO
r)
CO
X
<
1,000
100
TEST CONDITIONS
CASE BULK DENSITY INITIAL SOLIDS SYMBOL
(Ib/gal) CONCENTRATION (mg/l)
6 17.4 1.441.000 9
9 9 106.900
BOTH CASES USE A DISCHARGE RATE OF 1000bbl/h
AND A CURRENT VELOCITY OF 10cm/sec.
I
I
100
200
300
DISTANCE FROM DISCHARGE (m)
Figure 12. Maximum suspended solids concentration versus dis-
tance from the discharge for different bulk mud
density discharges at 10m.
28
-------
increases. Dissolved fraction dilution increases as water
depth increases for all distances.
Both particulate and dissolved fraction dilutions decrease
as discharge rate increases.
Particulate dilution at a given distance from the source
decreases as current velocity increases. However, for a
given travel time, larger particulate dilutions are obtained
in the higher velocity case. No direct relationship between
dissolved fraction dilution and current velocity could be
determined. The largest dissolved fraction dilutions were
obtained in the low velocity case, however.
Density stratification of the type and magnitude considered
in this report did not significantly affect either particulate
or dissolved fraction dilutions.
t Predilution of drilling mud has the same effect on solids
dilution as reducing the discharge rate by the appropriate
amount (as long as the mud discharge rates are equal).
This relationship holds for dissolved fraction dilutions
in deeper water [40 m (131 ft)], but in shallow water [10 m
(33 ft)], slightly lower dissolved fraction dilutions were
obtained for the predilution case. There appears to be
no practical advantage to predilution in waters deeper than
10 m (33 ft).
0 The initial solids concentration of the mud influences the
magnitude of dilution of both particulate and dissolved
fractions. As mud solids concentration (or mud bulk density)
increases, dilutions of both particulate and dissolved fractions
increase. However, lower water column concentrations of
suspended solids are achieved for the low mud density case
(lower initial solids concentration).
29
-------
Sensitivity Analysis
Multiple regression analysis was used to investigate the relationship
between predicted suspended solids concentrations at 100 m (328 ft) and
selected model input parameters. An analysis was conducted with both the
predicted depth-averaged and maximum suspended solids concentrations at
100 m (328 ft) from the discharge as the dependent variables, and current
velocity, discharge depth, and discharge rate as the independent variables.
These analyses were conducted with a sample size of 14.
The relative influence of the individual independent variables on
the total explainable variation (R2) in the multiple regression analysis
was also measured. The contribution of the correlation between each independent
variable and the predicted suspended solids concentrations was assessed
by weighting the individual correlation coefficients by the standardized
partial regression coefficient (often called the beta weights). The results
of these analyses indicate that there is no significant linear relationship
between the predicted suspended solids concentrations and the selected
independent parameters. Using the depth-averaged solids concentrations
at 100 m (328 ft) from the discharge as the dependent variable, the regression
analysis gave an R2 value of 0.52. Of this total explained variation,
water depth accounted for 3.1 percent, current velocity accounted for 20.4
percent, and discharge rate accounted for 76.5 percent. Using the maximum
suspended solids concentration at 100 m (328 ft) from the discharge as
the dependent variable, the regression analysis gave an R2 value of 0.43.
Of this total explained variation, water depth accounted for 6.2 percent,
current velocity accounted for 42.1 percent, and discharge rate accounted
for 51.7 percent.
The results of these regression analyses indicate that nonlinear relation-
ships between independent variables and criterion variables account for
48 to 57 percent of the total variation. However, discharge rate was shown
to be the dominant influence on the explained variability in suspended
solids concentration.
30
-------
EPA MODEL DESCRIPTION
The EPA model, developed and described by Yearsley (1984, pp. 1-16),
simulates the discharge of drilling muds to relatively shallow waters.
The model is applicable near the edge of the mixing zone and beyond for
shallow discharges with low densimetric Froude numbers. Under such conditions
several assumptions greatly simplify the computation. These assumptions
include the omission of the convective descent and dynamic collapse phases,
the immediate and uniform vertical mixing of solids upon discharge, and
the subsequent dominance of horizontal diffusion, advection, and particle
settling in the dilution process. The rationale for the omission of the
convective descent and dynamic collapse phases is that they generally occur
within 100 m (328 ft) of the point of discharge. In recognition of this
fact, the 100 m distance is often established as a mixing boundary. Outside
of the mixing zone of shallow discharges, vertical mixing is sufficient
to provide a uniform vertical distribution of solids. The EPA model formulation
assumes horizontal mixing occurs under isotropic turbulence. In contrast
to the OOC model, no upper and lower plume separation is -implicitly included
in the EPA model.
In comparison to the OOC model, input and output of the EPA model
are greatly simplified. Inputs to the model include data from three
categories: drilling mud characteristics, ambient characteristics, and
model options. Drilling mud characteristics consist of the source strength
(discharge flow rate multiplied by drilling mud concentration), the number
of discrete particle classes, and the distribution and settling velocities
of the particle classes. Ambient conditions are defined by the current
velocity, water depth, coefficient of eddy diffusivity, and background
suspended solids concentrations. Model options permit the specification
of the simulation duration, the number of time periods, the integration
time increments, and the distances from the discharge at which the drilling
mud concentrations are to be determined. Output from the model consists
of a tabular presentation of drilling mud concentrations at the preselected
distances and times. Concentrations of solids are depth-averaged values
computed along the plume centerline in the direction of the current.
31
-------
Limitations of the EPA model include an invariant water depth, and
constant discharge rate, and a unidirectional current of constant speed.
The distribution of cuttings is not incorporated into the EPA model. Unlike
the OOC model, dilution of the dissolved fraction is not computed by the
EPA model, nor is there any simulation of seabottom sediment accumulation.
Dissolved constituents are, in the short-term, conserved within the water
column, as no settling occurs, and thus dilution of dissolved solids is
always expected to be smaller than the suspended solids dilution predicted
by the EPA model. The EPA model has not undergone extensive verification
with field data. Comparisons made by Yearsley (1984, pp. 14-15) indicated
that the model generally predicts higher concentrations than those measured
in the field. Therefore, the dilutions predicted by the model tend to
be conservatively high. Near the discharge, however, maximum measured
concentrations were much higher than the depth-averaged results of the
model. This is a consequence of the model assumption that the drilling
mud is uniformly mixed throughout the water column. Thus, the EPA model
should not be used to predict drilling mud concentrations close to the
source [within 100 m (328 ft)].
32
-------
III. SOLIDS DEPOSITION
FIELD STUDIES
There have been no comprehensive field studies of bottom deposition
(areal extent and depth) of drilling mud discharges. Many studies involve
simple observation of the presence or absence of piles of drilling materials
near the source. Table 7 summarizes the findings of available deposition
studies.
There are several problems with interpretation and comparison of available
field study results of bottom deposition. Many studies were not designed
to fully describe bottom deposition patterns and characteristics. Sampling
time, frequency, location and procedures, and quantities measured often
differed among studies. In addition, the oceanographic and discharge conditions
varied widely from study to study and during each study. These factors
make it difficult to interpret results and determine the influence of different
factors on the bottom deposition characteristics. Detailed discussion
of available field studies is included in Appendix D. Problems with available
field data include poor study design, difficulty in measuring deposition
rates and sediment accumulation, variability of oceanographic conditions
during the tests, and small discharge volumes studied.
General conclusions supported by these field studies include:
Energy dynamics of the system strongly influenced bottom
deposition patterns. For example, no visible accumulation
of solids was observed near discharge sites in Cook Inlet
but deposited solids in the low energy mid-Atlantic remained
on the bottom for several years.
33
-------
TABLE 7. SUMMARY OF RESULTS OF DEPOSITION STUDIES
Site
Palawan Island,
Philippines3
Mid-Atlantic3
Georges Bank3
Canadian
Beaufort
Reference
Hudson et al .
(1982)
EGSG Environmental
Consultants (1982)
Bothner et al .
(1983)
Crippen et al .
(1980)
Sampling Method
Diver observation
Sediment samples,
television monitoring,
side-scan sonar
Sediment samples
Sediment samples
Length of
Deposition
Area (m)
20
100
500
--
Other
No visible cuttings
pile
Elevated barium levels
out to 1.6 km from
discharge
Elevated metals concen-
trations within 45m
Gulf of Mexico Tillery and
Thomas (1980)
Sediment samples
Reindeer Island Northern Technical Settling pans
Services (1981)
Tern Island
Norton Sound
Northern Technical Sediment samples
Services (1983)
Ecomar (1983)
Tanner Bank Ecomar (1978)
Cook Inlet3
Houghton et al,
(1980)
Sediment traps
Sediment traps
Sediment samples,
sediment traps,
television monitoring
from discharge
Decreasing gradient of
metals concentration
with distance from
the discharge
30 Maximum deposition of
173 mg/cm^ at 6 m
from discharge
No accumulation
observed
300 Accumulations ranged
from 2 to 1,740 g/m2.
Maximum at 12 m from
di scharge
125 Maximum deposition rate
of 67 g/m^/day at 64 m
from di scharge
No visible accumulation.
Cuttings deposition
ranged from 5.24xlO"3
g/m'/h to 1.25 g/m?/h
within 100 m of dis-
charge.
a Results for cuttings discharges only.
34
-------
Drilling effluents were generally deposited near the discharge
[within 100 to 1,000 m (328 ft to 3,281 ft)]. Deposition
patterns were determined by oceanographic conditions during
the study such as current velocity and water depth, and
discharge conditions such as discharge rate, volume, and
duration.
t Barium was the most common metal found in elevated levels
in sediments near drilling rigs. Other metals found in
elevated levels in sediments near drilling rigs included
cadmium, chromium, copper, lead, mercury, and zinc.
OOC MODEL RESULTS
Bottom deposition characteristics were predicted by the OOC model
for 20 cases listed in Table 6. Tabulated model results (deposition) for
these test cases are provided in Appendix B. The OOC model was used to
determine the relationship between bottom deposition and water depth, discharge
rate, current velocity, density stratification, predilution, and mud bulk
density (initial solids concentration).
Cumulative percent deposited solids versus distance from the discharge
was plotted to determine these relationships. These plots show the pattern
of solids accumulation including the areal extent of deposition. Figure 13
shows how the deposition pattern changes for mud discharges in various
water depths. For the 5 m (16 ft) depth, solids were deposited within
approximately 100 m (328 ft) of the discharge. Ninety percent of the deposited
solids settled within 15 m (50 ft). Maximum deposition was much greater
for this shallow water case than for the deeper cases. A majority of deposited
solids (90 percent) accumulated within 183 m (600 ft) for the 40 m (131 ft)
case and within 1,036 m (3,400 ft) for the 70 m (230 ft). Therefore, as
water depth increases, deposition area increases and deposition thickness
decreases for a given mud discharge. In addition, the location of maximum
deposition thickness moves farther downcurrent as water depth increases.
35
-------
Q
_j
o
Q
UJ
H
ay
CL
LU
Q
100 -
90 -
80 -
70 -
5°
QC
LU
o
40 -
30
20
10
TEST CONDITIONS
CASE
5
3
15
DEPTH(m)
5
40
70
SYMBOL
ALL CASES USE A DISCHARGE RATE OF
1000bbl/h AND A CURRENT VELOCITY
OF 10cm/sec
I
100
200
I
300
I
I
T
400 500 600 700
DISTANCE FROM DISCHARGE (m)
I
800
900
1000
Figure 13. Cumulative percent of deposited solids versus distance from the source
for different water depths.
-------
Figure 14 shows the relationship between solids deposition and ambient
current velocity. As expected, cases with higher current velocities result
in deposition of a lesser amount over a greater area. Therefore, as current
velocity increases, deposition area increases and deposition thickness
decreases. In addition, the location of maximum deposition moves farther
downcurrent as ambient velocity increases.
The relationship between bottom deposition and discharge rate is not
as clearly defined as those discussed previously. Figure 15 shows the
bottom deposition patterns for cases 3 (1,000 bbl/h discharge rate) and
4 (100 bbl/h discharge rate). Although the discharge rates differ by a
factor of 10, the deposition patterns are quite similar. The lower discharge
rate (case 4) scenario gives a slightly larger deposition area and lower
deposition thickness. In addition, the maximum deposition occurs within
31 m (100 ft) of the source for the low discharge rate scenario and within
61 m (200 ft) of the source for the higher discharge rate case.
Figure 16 shows the relationship between initial bulk density of the
mud (initial solids concentration) and solids deposition. This plot shows
that the deposition area is greater than double for the less concentrated
(lower initial solids concentration), lower density discharge. Maximum
deposition thickness is less (approximately half) for the lower density
discharge but the location of maximum deposition [31 m (100 ft)] is the
same for both cases. Therefore, as solids concentration increases, deposition
area decreases while deposition thickness increases.
The solids deposition results for deeper water cases [greater than
40 m (131 ft)] indicate that drilling solids settle in discrete zones (or
distances from the discharge) with no (or little) accumulation in between
these zones. This effect is a consequence of using discrete particle classes
(settling velocities) to represent a continuous distribution. As water
depth increases [depths greater than 40 m (131 ft)], individual particle
classes spend more time in the water column and become segregated due to
the different settling velocities as they settle to the bottom. Use of
a greater number of solids classes will alleviate this phenomenon.
37
-------
100
Q
£ 90-
0 8o -H
LU
0 70 -
LL
° 60-
|~
2
LU 50 -
O
o:
LU 40 -
O.
LU 30
"^ *J*J
^f ** rt
_j 20
_J ^
13
^
^ 10 -
0
A^^ _
>^ B m
/ ^
I /
1
1 /
I
r
/
-
1 TEST CONDITIONS
/ CASE VELOCITY (cm/sec) SYMBOL
/ ^ n n ^
10 ^ V
/ 12 30
BOTH CASES USE A DISCHARGE RATE OF
1 000 bbl/h AND A WATER DEPTH OF 1 5m.
1 1 I 1
100 200 300 400 5C
DISTANCE FROM DISCHARGE (m)
)0
Figure 14. Cumulative percent of deposited solids versus distance from the source
for different current velocities.
-------
en
Q
O
en 100
Q
111
If)
O
CL
UJ
Q
Lu
O
LU
O
90 -
80 ~
70 -
60
LU 50
cc
LU 40
30 -
20
10
7ESTCONDITIONS
CASE
3
4
DISCHARGE RATE (bbl/h)
1000
100
SYMBOL
BOTH CASES USE A WATER DEPTH OF 40m
AND A CURRENT VELOCITY OF 10cm/sec.
I
100
I
I
I
200 300 400
DISTANCE FROM DISCHARGE (m)
500
Figure 15. Cumulative percent of deposited solids versus distance from the source
for different discharge rates.
-------
C/3
Q
O
(/) 100
Q
LU
O
Q-
111
Q
LU
O
DC
LU
CL
90 -
80
70
60
50 -
40 -
LU 30 -
| 20
S 10
O
TEST CONDITIONS
CASE
6
9
BULK DENSITY
Ib/gal
174
9
INITIAL SOLIDS
CONCENTRATION (mg/l)
1,441,000
106,900
SYMBOL
BOTH CASES USE A DISCHARGE RATE OF 1000bbl/h
AND A CURRENT VELOCITY OF 10cm/sec.
I
100
I
200
300
400
DISTANCE FROM DISCHARGE (m)
Figure 16. Cumulative percent of deposited solids versus distance from the source
for different bulk mud densities.
-------
Deposition area and thickness are not significantly affected by the
variation considered in discharge rate, density stratification, or predilution
(change in initial solids concentration).
Summary
The effects of various factors such as water depth, discharge rate,
current velocity, density stratification, predilution, and initial mud
solids concentration on drilling mud deposition patterns may be determined
by comparing the OOC model results discussed above. Results of these model
runs support the following conclusions:
t As water depth or current velocity increases, deposition
area increases and deposition thickness decreases. The
location of maximum deposition moves downcurrent as water
depth or current velocity increases.
As initial mud solids concentration increases, deposition
area decreases and deposition thickness increases. The
location of maximum deposition is not affected by variation
in the initial mud solids concentration (bulk mud density).
t Solids deposition patterns were not significantly affected
by variation in the mud discharge rate or density stratifi-
cation. Deposition characteristics of the predilution case
(case 2) were also similar to the reduced total discharge
rate case (case 4).
41
-------
IV. FACTORS TO CONSIDER IN EVALUATING DISCHARGE LIMITATIONS
The most direct method to ensure that drilling mud discharges comply
with developed guidelines involves regulation of discharge characteristics
and discharge location. Drilling mud discharges can be closely regulated
or completely prohibited in or near "sensitive" environmental areas including
depositional areas, areas of low net circulation, or shallow waters. Discharge
characteristics that may be regulated include drilling mud type, mud toxicity,
initial solids concentration, discharge rate, and depth. First, discharge
guidelines must be developed and then, drilling mud dilutions must be predicted
for specific cases to determine compliance of possible discharge alternatives.
To determine discharge guidelines, drilling mud composition and toxicity
must be considered.
MUD COMPOSITION
Eight generic mud types have been evaluated during permit develop-
ment in EPA. Table 8 lists the basic components of each mud and their
maximum authorized concentrations. Each mud differs in its basic components,
and a single mud type can vary substantially in composition. For example,
the amount of barite in seawater/1 ignosulfonate mud can vary from 25-450
Ib/bbl.
The presence of potentially toxic trace elements in drilling muds
and cuttings is of primary concern. Metals including lead, zinc, mercury,
arsenic, and cadmium can be present as impurities in barite; chromium is
present in chrome lignosulfonates and chrome-treated lignite (Kramer et
al., 1980, p. 789; Crippen et al., 1980, pp. 639-640). According to Ayers
et al. (1980b, p. 389; Ecomar 1978, as cited by Petrazzuolo 1981, p. 3-3),
drill pipe dope (15 percent copper, 7 percent lead) and drill collar dope
(35 percent zinc, 20 percent lead, 7 percent copper) may also contribute
trace metals to the muds and cuttings discharge.
42
-------
TABLE 8. APPROVED DRILLING MUD TYPES
OCMPCNPTTS
Seawater/Freshwater/Potassium/Polymer Mud
KCL
Starch
Cellulose polymer
XC polymer
Drilled solids
Caustic
Barite
Seawater or freshwater
Seawater/LignosuIfonate Mud
Attapulgite or Bentonite
L i gnosu1fonate
Lignite
^ Caustic
oo Barite
Drilled solids
Soda ash/Sodium bicarbonate
Cellulose polymer
Seawater
Lime Hod
Lime
Bentonite
Lignosulfonate
Lignite
Caustic
Barite
Drilled solids
Soda ash/Sodium bicarbonate
Seawater or freshwater
Nondispersed Hud
Bentonite
Acrylic polymer
Barite
Drilled solids
Seawater or freshwater
MAXIMtM AimORIZED
GONCHflTOVTION
(pounds per barrel)
50
12
5
2
100
3
450
As needed
50
15
10
5
450
100
2
5
As needed
20
50
15
10
5
180
100
2
As needed
15
2
180
70
As needed
Spud Hud
Lime
Attapulgite or Bentonite
Caustic
Barite
Soda ash/Sodium bicarbonate
Seawater
Seawater/Freshwater Gel Mud
Lime
Attapulgite or Bentonite
Caustic
Barite
Drilled solids
Soda ash/Sodium bicarbonate
Cellulose polymer
Seawater or freshwater
Lightly Treated Lignosulfonate Freshwater/
Soawater Mud
Lime
Bentonite
Ligixjsu 1 f onate
Lignite
Caustic
Barite
Drilled solids
Soda ash/Sodiim bicarbonate
Cellulose polymer
Seawater to freshwater ratio
Lignosulfonate Freshwater Hud
Lime
Bentonite
L i giiosu 1 f ona te
Lignite
Caustic
Rarite
Drilled solids
C'olluloBe polymer
Srxla ash/Si ilium bicarbonate
Frf'sliw.il or
MAXIMtM AUTHORIZED
CONCEJTnwrinN
(pounds per barrel)
1
50
2
50
2
As needed
2
50
3
50
100
2
2
As needed
2
50
6
4
3
180
100
2
2
1:1-approximately
2
50
15
10
5
450
100
2
2
As
-------
Muds representative of generic muds 2 through 8 were analyzed for
trace metals as part of the mid-Atlantic bioassay program. While these
muds are "representative," the observed trace metal concentrations do not
represent the maximum concentrations that could occur. An estimate of
trace metal concentrations expected to occur in the drilling muds and cuttings
discharged from exploratory drilling operations is made here for subsequent
impact evaluation. Ideally, conservative values could be selected from
a large number of chemical analyses of muds and cuttings. This is not
possible, however, because only limited data are available on the trace
metal content of drilling muds and cuttings. Data from several sources
were combined to produce the expected maximum trace metal concentrations
in drilling mud presented in Table 9.
It should be noted that the concentrations presented in Table 10 represent
a whole mud analysis that includes constituents both in the dissolved and
particulate state. In the short term (over a few hours), dissolved metals
and their toxicity are of primary concern. Results of analyses for dissolved
pollutants associated with drilling muds are more limited than whole mud
analyses data.
The partitioning of metals between the solid and liquid phase in drilling
muds prior to discharge is expected to vary substantially from the partitioning
observed in seawater. The pH of drilling mud is generally about 10 while
the pH of seawater is approximately 8. Since pH is an important factor
controlling adsorption, observations at the pH of seawater are most appropriate
as an indicator of partitioning after discharge.
No detailed studies have been conducted to quantify the receiving
water concentrations of soluble metals associated with drilling muds.
Ayers et al. (1980a, p. 355) analyzed the filtrate of samples collected
near the discharge in the Gulf of Mexico for chromium. These samples contained
high solids concentrations before filtering. Concentrations of chromium
were below the 20 ppb detection limit of the analytical method used for
all filtrate samples.
44
-------
TABLE 9. MAXIMUM TRACE METAL CONCENTRATIONS
MEASURED IN DRILLING MUD DISCHARGES
Metal
Arsenic
Barium
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Vanadium
Zinc
Concentration
(ppm)
24
398,800
2.1C
1,300
88
820
1.53C
88
235
1,350C
Reference
a
b
b
d
d
a
b
d
d
b
a Crippen et al . (1980, p. 649). Reported as ug/g drilling fluid.
b Data derived from end-of-well chemical analyses reported to
EPA Region X in discharge monitoring reports (mg/kg dry weight
basis).
c Higher concentrations of cadmium, mercury, and zinc were measured
by Crippen et al. (1980, p. 649) but are not used here because the
barite used in Crippen1s study is not representative of drilling muds
used on the Alaskan outer continental shelf.
d Northern Technical Services (1981, p. 91) (ppm drilling fluid)
and Northern Technical Services (1982, p. 91) (mg/kg solid phase).
45
-------
TABLE 10. SOLUBLE AND SOLIDS METAL CONCENTRATIONS IN
DREDGED MATERIALS DUMPED AT SEA, 1978 AND 1979
Metal
Arsenic
Cadmi urn
Chromi urn
Copper
Mercury
Nickel
Lead
Zi nc
Average
Concentration
Solid Phase
rag/kg
4.0
1.2
33.0
30.4
0.3
15.0
29.6
68.8
Average
Concentration
Liquid Phase3
mg/1
0.0049
0.0016
0.0048
0.0027
0.0003
0.0068
0.0068
0.0325
Di ssol ved
Constituent
Concentration
Ratiob
0.0012
0.0013
0.0001
0.0001
0.0010
0.0005
0.0002
0.0005
a From results of elutriate test.
b Liquid phase:solid phase (mg/1:mg/kg).
Source: Bigham et al. (1982, pp. 292-294).
46
-------
In the absence of detailed information on the partitioning of metals
between the dissolved and participate phases of drilling muds and cuttings,
the metals partitioning characteristics of dredged material are used here
to develop estimates of dissolved metals concentrations associated with
drilling muds and cuttings. This is believed to be a reasonable approach
because of the physical similarities of the two materials. Dredged materials
are naturally-occurring sediments, sometimes contaminated, that are mechanically
or hydraulically picked up and transported to another site for disposal.
Dredged sediments are up to 80 percent water, and contain variable proportions
of sand, silt, and clay size particles, with organic matter concentrations
usually ranging from near 0 to 10 percent. The important similarity to
drilling muds and cuttings is that the majority of the bulk metals are
incorporated into the crystalline lattice of inorganic particles.
Table.10 presents concentrations of metals observed in the solid and
dissolved fraction of samples of dredged material dumped at sea in 1978
and 1979 (Bigham et al., 1982, pp. 292-294). The data represent approximately
50 separate analyses of sediments from the East and Gulf Coasts. The data
in Table 10 indicate that the partitioning varies from one metal to the
next but, in general, the dissolved fraction in mg/1 is approximately 0.1%
of the solid fraction in mg/kg.
Marine Water Quality Criteria
Table 11 summarizes the estimated maximum trace metal concentrations
of the whole mud and the dissolved fraction and also lists the federal
marine water quality criteria. Using the dissolved fraction concentrations,
a minimum dilution of only 72:1 would be needed to comply with the federal
24-h saltwater criteria. State criteria for specific sites should also
be considered. Therefore, it does not appear that dilution of the dissolved
fraction of discharged drilling muds will be a limiting factor at the edge
of the 100 m (328 ft) mixing zone.
47
-------
CXI
TABLE 11. TRACE METAL CONCENTRATIONS OF THE WHOLE MUD AND
DISSOLVED FRACTION AND FEDERAL MARINE WATER QUALITY STANDARDS
Metal
Arsenic
Barium
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Vanadium
Zinc
Concentration
Whole Mud Dissol
(mg/kg)
24
398,800
2.1
1,300
88
820
1.53
88
235
1,350
ved Fraction3
(mg/1)
0.024
399
0.0021
1.3
0.088
0.82
0.00153
0.088
0.235
1.35
Federal
Saltwater Criteria13
Maximum Al lowable
508
No criteria
59
1,260 (hexavalent)
23
668
3.7
140
No criteria
170
(ug/1)
24-h Criteria
No criteria
No criteria
4.5
18 (hexavalent)
4.0
25C
0.1
7.1
No criteria
58
a Estimated as 0.001 times the whole mud concentration (see Table 10).
b From 45 Federal Register 79318.
c Chronic toxicity criteria.
-------
TOXICITY OF DRILLING MUDS
Section 125. 123(d) (1 ) of the Ocean Discharge Criteria requires, if
a determination regarding unreasonable degradation cannot be made, that
the discharge must pass certain bioassay-based requirements. Although
this requirement does not apply to all cases of ocean discharge of drilling
mud and cuttings, the procedure may be applied to all cases as an approximate
guideline and also provide a means of comparing potential impacts of exploratory
drilling between different general permit areas.
The bioassay-based requirements are based upon the limiting permissible
concentrations (LPC) concept of the Ocean Dumping Regulations. The application
of the LPC concept to drilling mud discharges can be summarized as follows.
The results of acute bioassay tests of various drilling muds provide a
mud concentration which causes mortality to 50 percent of the organisms
tested. This concentration, referred to as the LC5Q (lethal concentration),
is also specific to the duration of the test which is commonly 96 hours.
Bioassay tests applicable to Alaska marine organisms range from 48- to
144-h duration. Since the IC^Q is the point where half the test organisms
died, the LPC value is obtained by applying a safety factor (0.01) to the
LC5Q value1. In other words, the LPC value is one one-hundredth of the
LC5Q and is designed to preclude both acute and chronic toxicity impacts.
The mixing zone extends 100 m (328 ft) in all directions from the
discharge point^. The concentration of muds 100 m (328 ft) from the discharge
is determined with an appropriate dispersion model or based upon results
of field studies. This concentration should then be less than the specified
guideline concentration.
Drilling muds are usually discharged intermittently in large quantities
(roughly 1,000 bbl) when the mud system is changed, although small quantities
may be discharged steadily with cuttings from solids control equipment
regulations allow the use of other than 0.01 if applicable (40 Federal
Register 659f4 and 42 Federal Register 2481).
^The regulations allow that the mixing zone may be defined by the boundary
of the zone of initial dilution as calculated by an approved plume model
(40 Federal Register 65953).
49
-------
(Ayers et al . 1980a) . Large-scale discharges during mud change-over may
occur at rates up to approximately 1,000 bbl/hr. It would appear, therefore,
that measures of acute toxicity (LCso) would be of greater concern for
drilling mud discharges because exposure to drilling muds in the water
column are not chronic (LPC) in the usual sense of the term. Therefore,
a representative minimum 1050 will be selected as the guideline for the
allowable drilling mud solids concentration at 100 m (328 ft) from the
discharge.
A variety of Alaskan marine organisms have been exposed to drilling
mud in laboratory or field experiments. Most of these studies (Environmental
Protection Service 1975; EG&G Marine Research Laboratory 1976; EG&G Bionomics
1976a, 1976b; Tornberg et al. 1980; Gerber et al. 1980; Houghton et al. 1980;
Neff et al. 1980; Crawford and Gates 1981; Northern Technical Services
1981; Carls and Rice 1984) have addressed short-term acute effects in a
"screening" sense in the laboratory. Carls and Rice (1984) obtained the
lowest LCso values for an Alaskan species (600 ppm vol :vol for dock shrimp
larvae, Pandalus danae). however, it is suspected that the mud was treated
with a chromium-rich special additive that has since been reformulated
to exclude chromium (Hulse, M., 1983, personal communication). The Carls
and Rice (1984) LC5Q data may not represent those expected on the Alaskan
outer continental shelf. More likely representative lowest LCso values
are 1,100 mg/1 (3,000 ppm volrvol) noted for pink salmon fry, Oncorhynchus
gorbuscha, by Houghton et al. (1980).
While the LCsg-type analysis is generally reasonable, some problems
arise in its application to drilling mud discharges. First, the duration
of high rate discharges is much less than the test period of the bioassay.
Bulk discharges of mud generally do not exceed 1,000 bbl. At a discharge
rate of 1,000 bbl/h, the period of discharge does not exceed 1 h. This
period represents only from 2.1 to 0.7 percent of the bioassay period for
Alaska organisms (48 to 144 h). It appears, therefore, that some adjustment
should be made to the LC5Q-type analysis to account for the difference
in exposure time.
50
-------
Unfortunately, no standard method is available to adjust an LC5g value
to reflect shorter exposure times. Results of most applicable bioassay
tests do not report the mortalities observed at times less than the full
duration of the test. Where these data are available, large differences
occur between the exposure time-mortality relationship for different organisms.
Thus, any adjustment to the LCsg-type analysis must be somewhat artificial
and judgmental.
A second exposure time-related problem occurs with the 1050 analysis.
When concentrations of solids discharged from a fixed point are observed
at another field point (100 m) downstream, the downstream concentration
will be related to the current velocity. For a 2 cm/sec current, which
may represent under-ice conditions in the Beaufort Sea, the time required
to travel 100 m is 5,000 sec or 83 min. For a 10 cm/sec current, which
may represent moderate-energy open water currents, the travel time decreases
to 1,000 sec or 17 min. At high current velocities around 30 cm/sec which
occur in Cook Inlet and elsewhere in Alaska, the travel time to 100 m is
further reduced to 333 sec or 6 min. If these travel times are now compared
to the exposure times used in the bioassays (48 to 144 h), the 100 m distance
from the discharge appears extremely conservative for higher current regimes.
Since impacts to water column organisms are related to exposure time, as
indicated by bioassay tests, the regulatory procedure used to evaluate
these impacts should also take exposure time into account. At the same
time it should be realized that the mixing zone concept is still useful
for purposes of impact analysis and monitoring purposes.
The 1050 mixing zone concept could be very flexible if bioassay data
were available for shorter exposure times. For example, an exposure time
of one hour would be a closer, but still conservative, approximation of
actual exposure times. In the absence of these bioassay data, the only
remaining flexibility is in the size of the mixing zone and the safety
factor. Therefore, using the minimum LCso for 48- to 144-h duration bioassays
as a receiving water suspended solids guideline will result in a conservative
value for typical drilling mud discharges of 1-h or less duration.
51
-------
Based on the bioassay results discussed above (Alaskan species), the
lowest representative 1050 for generic muds is 1,100 tng/1. If the initial
drilling mud solids concentration is conservatively assumed to be 1,441,000 mg/1
(highest concentration used in the field studies summarized in Table 1),
the 1,100 mg/1 criteria may be represented as a minimum particulate dilution
of approximately 1,300:1 at the edge of the 100 m (328 ft) mixing zone.
BOTTOM DEPOSITION
No studies have been conducted to determine the magnitude or duration
of solids accumulation on the seafloor that will adversely affect benthic
biota. Table 12 summarizes the results of a few major field investigations
on environmental fate and effects of drilling fluids and cuttings discharges.
The results of most studies show that drilling solids accumulations generally
occur within 1,000 m of the discharge site. Only two of the eight studies
summarized showed some impact to benthic biota near the discharge site,
however, impacts were observed only in a limited area. These studies support
the following general conclusions:
Solids accumulation is directly influenced by the oceanographic
conditions at the drilling site and the quantity of material
discharged. High energy environments tend to disperse drilling
effluents over a large area and may resuspend or transport
the solids out of the study area.
Elevated levels of trace metals (especially barium) are
commonly present in sediments near drilling rigs. However,
there is no direct correlation between elevated levels of
trace metals in sediments and impacts to the biota.
t Impacts on benthic biota are limited to areas directly adjacent
to the discharge site.
52
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TABLE 12. SUMMARY OF MAJOR FIELD INVESTIGATIONS OF THE ENVIRONMENTAL
FATE AND EFFECTS OF DRILLING FLUIDS AND CUTTINGS
DISCHARGED TO THE ENVIRONMENT
Location
Objectives
Physical Characteristics
Results
References
in
OJ
East Flower Garden
Bank, NM Gulf of Mexico
Palawan Island,
Philippines
Loner Cook Inlet, AK
Mid-Atlantic DCS
Georges Bank,
North-Atlantic DCS
U.S. Beaufort Sea, AK
Canadian Beaufort Sea
Central Gulf of Mexico
Fate of drilling fluids
shunted to 10 m above
bottom; effects on coral
reef 2,100 m away
Effects of drilling dis-
charges on coral reefs
Fate of drilling discharges
and effects on benthic
communities
Fate of drilling discharges;
effects on benthic community;
bioaccumulation of metals
Fate of drilling discharges;
effects on benthic community;
bioaccumulation of metals
Effects of above-ice and
below-ice disposal of drill-
ing mud and cuttings on
benthic communities; bio-
availability of metals
Metals from drilling dis-
charges in sediments and
benthos
Distribution of metals in
sediments and biota In oil
production fields
Drilling at 129 m water depth; coral
zone at 20-50 m and NM of drill site;
bottom currents toward WSW drill site
Drilling directly on reef at 26 m; two
wells drilled 3 m apart; 3 cm/sec currents
to the north
Drilling at 62 m water depth, 4.6-5.3 m
tides, mean maximal tide currents 42-104
cm/sec between bottom and surface. Discharge
rate varied from 20 to 1,200 bbl/h.
Drilling at 120 m water depth; bottom
currents < 10 cm/sec 62 percent of time,
sediments 20 percent silt/clay. Discharge
rates were 275 and 500 bbl/h.
Rigs at 80 and 140 m monitored; residual
bottom current 3.5 cm/sec. Frequent
severe storms; sediments < 1 percent
silt/clay
Water depth 5-8 m; ice cover most of
year with bottom scour in shallower areas.
Near-bottom currents were 4 to 5 cm/sec.
Discharge rates were 1,510 and 21 bbl/h.
Drilling from artificial island; rapid
seasonal erosion ad ice scour
Shallow water, high suspended sediment
load. Study sites located in less than
18 to 92 m depth. Current velocities
ranged from 0 to 20 cm/sec. Discharge
rates varied from 2/b to 1,00(1 bbl/h.
Drill fluids and cuttings distribu-
ted to 1,000 m from discharge
70-90 percent reduction in some
species of living corals within 115
by 85 m area; epifauna associated
with corals affected to 40 m; no
drill cuttings pile. Cuttings
present within 20 m of the wells.
Little accumulation of mud and
cuttings on bottom; no effects on
benthos attributable to discharges;
cuttings deposition rate ranged
from 5.24 x 103 to 3.2 x lO"?
g/h/m2 with distance from discharge.
Visible cuttings piles within 100 m
elevated Ba in sediments to 1.6 km;
abundance of predatory demersal spp.
increased; large decrease in abun-
dance of benthic infauna near rig
with some bioaccumulation of Ba and
possibly Cr by benthic infauna.
Evidence of cuttings within 500 m
of rigs; elevated Ba in bulk sedi-
ments to 2 km; no effects on benthos
attributable to drilling; no
bioaccumulation.
0.5-6 cm fluid and cuttings on bottom
but carried away quickly; no effects
attributable to discharges on benthos;
possible uptake of Ba by macroalgae
and Cu by amphipods; maximum deposi-
tion of 173 mg/cm2 at 6 m from the
discharge. Little deposition at
distances greater than 30 m from the
discharge.
Elevated levels of Hg, Pb, Zn, Cd,
As, and Cr in sediments near dis-
charge (within 4b m) with elevated
Hg to 1,800 m; no correlation
between metals in sediments and
biota; coarse grained material from
island observed out to 300 m.
Decreasing concentration gradients
of Bd, Cd, Cr, Cu, Pb, and Zn in
sediments around some rigs. Metals
not elevated in commercial species
of shrimp and fish.
Gettleson (1978)
Hudson et al. (1982)
Dames & Moore (1978)
Houghton et al. (1980)
Lees and Houghton (1980)
EGSG Environmental
Consultants (1982)
Battelle/W.H.O.I. (1983)
Bothner et al. (1983)
Payne et al. (1982)
Northern Technical
Services (1981)
Crippen et al. (1980)
Tillery and Thomas (1980)
-------
SUMMARY OF OOC MODEL RESULTS
Minimum solids dilutions at 100 m (328 ft) from the discharge as predicted
by the OOC model are summarized in Table 13 for each case. Results of
OOC model runs discussed in this report showed that the density stratification
considered did not significantly affect dilution. Particulate dilution
was shown to increase as discharge rate or current velocity decreased.
The relationship between particulate dilution and water depth was not as
clear. In waters shallower than 20 m (66 ft), particulate dilution generally
increased as water depth decreased. However, in water 40 to 70 m (131 to
230 ft) deep, the opposite is true. This indicates that care should be
taken when using the OOC model predictions for shallow water. The model
cannot accurately simulate discharges to shallow, low velocity waters where
the plume descends vertically and encounters the bottom.
EPA MODEL RESULTS
Results of EPA model simulations are shown in Figure 17 for a 10 cm/sec
(0.33 ft/sec) ambient current speed and Figure 18 for a 2 cm/sec (0.07 ft/sec)
ambient current speed, for water depths from 2 to 20 m (7 to 66 ft), and
discharge rates (Q) from 250 to 1,000 bbl/h. These results show that the
depth-averaged solids dilution increases linearly as water depth increases.
Solids dilution [at 100 m (328 ft)] generally increases as discharge rate
decreases or current velocity increases [except for the highest discharge
rate (1,000 bbl/h) case. The EPA model gives much lower solids dilutions
(more conservative) than those predicted by the OOC model for comparable
cases (see Table 14).
EFFECTS OF ICE COVER ON DRILLING MUD DILUTION
The presence of ice cover generally affects drilling mud dilution
and solids deposition by eliminating wind-driven current velocities and
decreasing the total water depth available for dilution. Currents and
circulation should not be altered substantially by the presence of drift
ice. However, the presence of pack ice will eliminate wind driven circulation
54
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TABLE 13. SUMMARY OF MINIMUM SOLIDS DILUTIONS PREDICTED BY
THE OOC MODEL AT 100 in (328 ft) FROM THE DISCHARGE3
en
01
Case
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Water
Depth
(m)
40
40
40
40
5
10
10
10
10
15
15
15
20
40
70
120
120
5
15
15
Discharge
Rate
(bbl/h)
1,000
1,000
1,000
100
1,000
1,000
1,000
100
1,000
1,000
1,000
1,000
1,000
1,000
1,000
1,000
1,000
250
250
250
Surface
Current
(cm/sec)b
2
10
10
10
10
10
10
10
10
2
10
30
10
10
10
10
32
10
2
10
Density
btrati f ication,
Aot
(Bottom to
Surface)
3.9
3.9
3.9
3.9
0.1
0.7
0.7
0.7
0.7
1.07
1.07
1.07
1.00
0.5
2.5
0.98
1.30
0.1
1.07
1.07
Minimum Solids
Dilution at
100 m (328 ft) Comments
2,015C Prediction 9:ld
532e Prediction 9:ld
905
5,246
4,810
1,785
3601" Prediction 9:ld
3,859
299 Mud bulk density = 9 Ib/gal
11,407
1,748
752
1,092
731 Minimum stratification (40 m)
1,803
1,437
5,793
6,109
8,873
2,558
a Al 1 cases use
concentration 1
b Uniform veloci
near
c Di lut
d Nine
e Dilut
f Dilut
the bottom
ion due to
a 2.09 g/cm3
,441,000 mg/1)
ty distributi
the receiving
parts water with 1 part
ion due to
ion due to
the receiving
the receiving
(17.4 Ib/gal)
on with depth
water only.
mud.
water only.
water only.
mud unless otherwi
was assumed , with
Total dilution is
Total dilution is
Total dilution is
se specified (initial solids
a sharp decrease in velocity
20,150:1.
5,320:1.
3,600:1.
-------
10,000 -|
8.000 -
6.000 -
o
h-
D
Q
03
o
O)
Q
LU
cn
tu 4.000
Q.
LU
Q
2.000 -
Q = 250 DDl/h
Q = 500bbl/h
Q = 1.000bb1/h
10
15
I
20
WATER DEPTH (m)
TEST CONDITIONS
CURRENT SPEED
WATER DEPTH
DISTANCE FROM DISCHARGE
10 cm sec
2 to 20m
100m
Figure 17. Depth-averaged solids dilution at 100 meters from
discharge predicted by the EPA model for 10 cm/sec
current speed.
56
-------
8,000 1
tr 6,000 -
_j
Q
CO
9
d
CO
Q 4.000
LU
cc
LU
Q.
LU
Q
2.000 -
Q = 250bbl/h
M Q = 500bbl/h
@ Q = LOOObbl/h
I
10
\
15
I
20
WATER DEPTH (m)
TEST CONDITIONS
CURRENT SPEED
WATER DEPTH
DISTANCE FROM DISCHARGE
Figure 18. Depth-averaged solids dilution at 100 meters from
discharge predicted by the EPA model for 2 cm/sec
current speed.
57
-------
TABLE 14. COMPARISON OF DEPTH-AVERAGED SOLIDS DILUTIONS AT 100 m
(328 ft) FROM THE DISCHARGE FOR THE OOC AND EPA MODELS
Water
Depth (m)
5
5
10
15
15
15
15
20
Current
Speed (cm/sec)
10
10
10
2
2
10
10
10
Discharge
Rate (bbl/h)
250
1,000
1,000
250
1,000
250
1,000
1,000
Depth-Averaged
at 100 m (328 ft)
EPA Model
2,831
708
1,310
4,649
2,984
7,625
1,906
2,502
Solids Dilut
from the Dis
OOC Model
20,121
14,943
5,190
29,349
23,517
13,040
5,661
4,674
ion
charge
58
-------
over ice covered areas and dampen wave activity. In addition, tidal currents
may be reduced beneath ice cover. The fractional force of the ice cover
on the water surface also acts to decrease current speeds. All of these
effects will reduce circulation (current velocities) and result in decreased
dispersion and increased near-field deposition of drilling mud discharges.
Available monitoring data from SOHIO's Mukluk Well No. 1 (SOHIO, 1984)
were evaluated to determine current velocities under ice in Harrison Bay
of the Beaufort Sea. Currents were monitored at a depth of approximately
12.2 m (40 ft) in 14.0 m (46 ft) of water from September 20, 1983, through
February 16, 1984. Ice conditions varied throughout the monitoring period.
By mid-October there were a few inches of ice cover and by the first of
November there was a solid ice cover approximately 0.3 m (1 ft) thick.
By January there was a 1.8 m (6 ft) thick layer of ice with ice ridges
up to 6.1 m (20 ft) thick which lasted through June (Wagner, M., 8 August
1984, personal communication). Current velocities ranged from 1.5 to 39.7
cm/sec with monthly average speeds decreasing steadily from 11.9 cm/sec
in September to 2.5 cm/sec in February. These data indicate that as the
ice cover grew thicker and more stable, the current velocity decreased
(see Figure 19), and that a current velocity of 2 cm/sec, as used in the
modeling efforts, is representative of under-ice current velocities in
shallow Alaskan waters.
Under these conditions (2 cm/sec current velocity), the EPA model
predicted depth-averaged particulate dilutions at 100 m (328 ft) from the
discharge point ranging from 741 to 3,812:1 for the maximum discharge rate
(1,000 bbl/h) and water depths ranging from 2 to 20 m (7 to 66 ft) (see
Figures 17 and 18). These dilutions are much lower than those predicted
by the OOC model (Table 14), but the OOC model results are less reliable
in shallow, low velocity waters.
59
-------
O
0)
O)
b
O
3
LU
UJ
DC
or
D
O
LJJ
DC
UJ
I
H-
12 -
11
10 -
8 -
7 -
6
5
4 -
3-
2 -
1 -
ICE THICKNESS
CURRENT VELOCITY
SEPTEMBER OCTOBER NOVEMBER DECEMBER JANUARY FEBRUARY
TIME OF YEAR
- 20
1 8
1.6
- 1.4
1 2
- 10
8
6
4
.2
UJ
z
O
I
UJ
Figure 19. The relationship between ice cover, current velocity, and time of year.
-------
V. RECOMMENDATIONS
RECOMMENDED DISCHARGE REGULATIONS
Data presented in this report indicated that varying the discharge
rate significantly affected both the dissolved and particulate dilutions,
but did not substantially affect the solids deposition area or thickness.
Dissolved fraction dilution does not appear to be a limiting factor at
the edge of the 100 m (328 ft) mixing zone. As discharge rate increased
(in the range of 100 to 1,000 bbl/h), the dilution decreased. Therefore,
specifying a maximum allowable discharge rate would ensure that the drilling
effluent would undergo a minimum specified dilution (or not exceed a maximum
specified receiving water concentration) at the edge of a mixing zone.
Predilution of drilling muds involves mixing seawater with drilling mud
prior to discharge to decrease the initial solids concentration. Results
discussed in this report showed that for a given volume of mud discharged,
predilution and lowering the discharge rate had a similar effect on dilution.
Predilution (9:1) with a high discharge rate (1,000 bbl/h) and no predilution
with a low discharge rate (100 bbl/h) both resulted in similar effluent
dilutions with distance from the source. Therefore, there seems to be
no practical advantage to predilution of drilling mud discharges and recommenda-
tions made in this report will be in terms of a maximum allowable discharge
rate for a given water depth.
Maximum allowable discharge rates were determined using the results
from the EPA model simulations (2 and 10 cm/sec current velocities) for
water depths less than 20 m (66 ft) and the results from the OOC model
simulations (10 cm/sec current velocity) for water depths from 20 to 120 m
(66 to 394 ft). Neither model is applicable for water depths less than
2 m (6.6 ft). For shallow waters [less than 20 m (66 ft) deep], EPA model
results (see Figures 17 and 18) indicate that particulate dilutions at
61
-------
100 m (328 ft) from the source are less than the recommended 1,300:1 dilution
for the following cases:
A discharge -rate of 1,000 bbl/h (or greater) and water depths
between 2 and 5 m (6.6 and 16 ft).
t A discharge rate of 250 bbl/h (or greater) and a water depth
of 2 m (6.6 ft).
For deeper waters [20 to 120 m (66 to 394 ft) deep], the OOC model results
(see Table 13) indicate that particulate dilution at 100 m (328 ft) from
the source are less than the recommended 1,300:1 dilution for the following
case:
t A discharge rate of 1,000 bbl/h (or greater) and water depths
between 20 and 40 m (66 to 131 ft).
Based on these results, a maximum discharge rate of 250 bbl/h is recom-
mended for water depths from 2 to 5 m (7 to 16 ft). For water depths between
5 and 20 m (16 and 66 ft), the discharge rate should not exceed 500 bbl/h.
The recommended maximum discharge rate for water depths from 20 to 40 m
(66 to 131 ft) is 750 bbl/h. A maximum discharge rate of 1,000 bbl/h is
recommended for water depths between 40 and 120 m (131 to 394 ft). The
deepest case considered in this analysis was 120 m (394 ft).
Model results discussed in this report indicate that ambient current
speed directly affects dilution of both the dissolved and particulate fractions
of drilling mud discharges. The EPA model generally predicted higher solids
dilutions in waters with higher current speeds (except for the 1,000 bbl/h
discharge rate). The OOC model predicted lower dilutions in waters with
higher current speeds. These results indicate that in shallow waters [less
than 20 m (66 ft) deep], the recommended discharge rates could be increased
as ambient current speed increased and still meet the recommended 1,300:1
dilution. Similarly, for deeper waters [20 to 120 m (66 to 394 ft) deep],
the recorrmended discharge rates could be decreased as ambient current velocity
increased. The degree to which these rates could be increased or decreased
62
-------
cannot be determined from the available data since changing the discharge
rate will also affect dilution.
OOC MODEL SIMULATIONS
The input variables of primary interest to the regulation of discharges
(water depth, current velocity, and discharge rate) have been considered
in this report. Many site specific input variables available in the OOC
model format have not been evaluated. Future simulations using this model
may incorporate these parameters to assess the effect of these variables
on drilling mud dilution and solids deposition. Discharge characteristics
of interest for future simulations include rig type (jackup versus semisub-
mersible), discharge nozzle radius and orientations, shunting of discharges,
and use of denser (or finer) solids in the drilling mud (different particle
size distributions). Oceanographic characteristics not evaluated in detail
for this report include variation of density stratification profiles with
time, sea-state conditions, change in water depth within the model grid,
layered vertical current velocity distribution, and density stratification
involving a strong gradient such as a pycnocline or thermocline. OOC model
simulations incorporating these parameters will add to our understanding
of the processes affecting drilling mud dilution and bottom deposition.
To augment the data gathered from the simulations presented in this
report, it would be helpful to conduct more OOC model simulations using
water depths between 15 and 70 m (49 and 230 ft) and discharge rates between
100 and 1,000 bbl/h. These runs will help fill in some of the information
gaps and better define the water depth ranges and associated discharge
rate limits. Simulations using water depths of several hundred meters
will help define the potential for dilution of mud discharges in the deeper
waters of many lease sale areas.
FIELD STUDIES
Neither the OOC or EPA mud dispersion models have been adequately
verified in the field. Several field data sets have been collected (see
Table 1 and Appendix C and D) but none have provided information in adequate
63
-------
detail for meaningful model calibration. The OOC model is considered to
provide reasonable results, but this opinion is based on the structure
of the model and comparison of model results to laboratory data of Fan
(1967), Koester (1976), and Davis (1983) (see MMS, 1983) and not on comparison
to field data. Collection of an adequate data set and comparison to model
results is strongly recommended to properly verify both models.
For Alaskan waters, model verification is most needed for shallow-water
cases; from 2 to about 40 m (7 to 131 ft). In deeper waters, dilutions
are generally large enough to alleviate concern. A verification study
in waters between 10 and 20 m (33 to 66 ft) would probably be most practical
and useful.
It is not necessary that the verification study be performed in Alaskan
waters. In fact, from a logistical point of view, the chance of a field
test being successful would be greater in Gulf of Mexico or California
waters.
The field verification study should provide an approximate mass balance
of drilling mud discharged under steady-state conditions and over distances
between about 50 to about 200 m (164 to 656 ft) downcurrent of the discharge.
The steady-state condition means that mud should still be discharging when
the leading edge of the mud cloud reaches 200 m (656 ft) downcurrent of
the discharge. If the average current speed were 10 cm/sec (0.33 ft/sec),
plume sampling would commence following about 30 minutes of discharge.
Mud discharge should continue at a constant rate throughout the sampling.
Field data collection should allow for verification of predicted water
column dilutions and bottom deposition.
64
-------
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of Effluent Dispersion and Fate Models for DCS Platforms, Santa Barbara, CA.
February 7-10, 2 Vols.
Neff, J.M., W.L. McCulloch, R.S. Carr, K.A. Retzer, and J.R. Sharp. 1980.
Effects of used drilling muds on benthic marine animals. Publ. No. 4330.
Prepared for Amer. Petroleum Inst., Washington, D.C. 31 pp.
Northern Technical Services. 1981. Beaufort Sea drilling effluent disposal
study. Prepared for Reindeer Island stratigraphic test well participants
under direction of SOHIO. Alaska Petroleum Co. 329 pp.
Northern Technical Services. 1982. Above-ice drilling effluent disposal
tests-Sag Delta No. 7, Sag Delta No. 8, and Challenge Island No.l wells,
Beaufort Sea, Alaska. Prepared for SOHIO Alaska Petroleum Company, Anchorage,
AK. 185 pp.
67
-------
Northern Technical Services. 1983. Open-water drilling effluent disposal
study. Tern Island, Beaufort Sea, Alaska. Prepared for Shell Oil Company,
Anchorage, AK. 87 pp.
Payne, J.R., J.L. Lambach, R.E. Jordan, G.D. McNabb, Jr., R.R. Sims, A. Abasu-
mara, J.6. Sutton, D. Generro, S. Gagner, and R.F. Shokes. 1982. Georges
Bank monitoring program, analysis of hydrocarbons in bottom sediments and
analysis of hydrocarbons and trace metals in benthic fauna. First Year
Report to the New York OCS Office, Minerals Management Service, U.S. Department
of Interior, (not seen).
Petrazzuolo, G. 1981. Preliminary report: an environmental assessment
of drilling fluids and cuttings released onto the outer continental shelf.
Prepared by U.S. EPA office of Water and Waste Management and the Office
of Water Enforcement and Permits. 104 pp.
Ray, J.P., and R.P. Meek. 1980. Water column characterization of drilling
fluids dispersion from an offshore exploratory well on Tanner Bank. pp. 223-
258. In: 1980 Symposium - Research on Environmental Fate and Effects
of Drilling Fluids and Cuttings. Lake Buena Vista, FL.
SOHIO Alaska Petroleum Co. 1984. Progress report, Drilling effluent discharge
monitoring Mukluk Island, Harrison Bay, Anchorage, AK.
Tillery, J.B., and R.E. Thomas. 1980. Heavy metal, contamination from
petroleum production platforms in the Gulf of Mexico, pp. 562-587. In:
1980 Symposium - Research on Environmental Fate and Effects of Drilling
Fluids and Cuttings, Lake Buena Vista, FL.
Tornberg, L.D., E.D. Thielk, R.E. Nakatani, R.C. Miller, and S.O. Hellman.
1980. Toxicity of drilling fluids to marine organisms in the Beaufort
Sea, Alaska, pp. 997-1016. In: 1980 Symposium - Research on Environmental
Fate and Effects of Drilling Fluids and Cuttings. Lake Buena Vista, FL.
Wagner, M. 8 August 1984. Personal Communication (phone by Ms. Lys Hornsby).
SOHIO Alaska Petroleum Company, Anchorage, AK.
Yearsley, J.R. 1984. A time-dependent, two-dimensional model for predicting
the distribution of drilling muds discharged to shallow water. EPA Region X,
Seattle, WA.
68
-------
APPENDIX A
MINIMUM DILUTIONS AS PREDICTED BY
THE OOC MODEL
-------
TABLE A-l. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 1*
Distance
On)
15.2
45.7
100.0
137.2
182.9
243.8
304.8
426.7
from Discharge
(ft)
50
150
328
450
600
800
1,000
1,400
Minimum
Particulate
165
565
2,015
3,520
6,030
9,575
14,645
29,290
Dilution**
Dissolved
200
635
2,170
3,745
6,240
9,625
14,310
26,450
*MODEL INPUTS: Water Depth = 40 m
Total Discharge Rate = 1,000 bbl/h
Mud Discharge Rate = 100 bbl/h
Prediction 9:1
Surface Current = 2 cm/sec
Forced Separation.
**Dilutions are due to receiving water only. To obtain total
dilution (to include predilution) multiply all dilutions by
10.
A-l
-------
TABLE A-2. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 2*
Distance
(m)
15.2
45.7
100.0
137.2
182.9
304.8
609.6
914.4
from Discharge
(ft)
50
150
328
450
600
1,000
2,000
3,000
Minimum
Particulate
190
337
532
973
1,014
1,566
4,008
7,307
Dilution**
Dissolved
262
383
726
1,041
1,311
2,045
4,810
7,294
*MODEL INPUTS: Water Depth = 40 m
Total Discharge Rate = 1,000 bbl/h
Mud Discharge Rate = 100 bbl/h
Predilution 9:1
Surface Current = 10 cm/sec
Forced Separation.
**Dilutions are due to receiving water only. To obtain total
dilution (to include predilution) multiply all dilutions by
10.
A-2
-------
TABLE A-3. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 3*
Distance
(m)
15.2
45.7
100.0
137.2
182.9
304.8
609.6
914.4
from Discharge
(ft)
50
150
328
450
600
1,000
2,000
3,000
Minimum
Particulate
417
654
905
1,176
1,469
2,689
13,528
18,098
Dilution
Dissolved
185
679
1,285
1,672
1,949
3,180
12,557
10,992
*MODEL INPUTS: Water Depth = 40 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Forced Separation.
A-3
-------
TABLE A-4. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 4*
Distance
(m)
15.2
45.7
100.0
137.2
182.9
304.8
609.6
914.4
from Discharge
(ft)
50
150
328
450
600
1,000
2,000
3,000
Minimum
Particulate
1,642
2,950
5,246
7,869
8,577
14,472
42,445
79,525
Dilution
Dissolved
1,911
4,177
7,423
10,503
9,610
15,997
37,685
59,393
*MODEL INPUTS: Water Depth = 40 m
Discharge Rate = 100 bbl/h
Surface Current = 10 cm/sec
Forced Separation.
A-4
-------
TABLE A-5. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 5*
Distance
(m)
15.2
30.5
61.0
100.0
137.2
182.9
243.8
304.8
457.2
609.6
from Discharge
(ft)
50
100
200
328
450
600
800
1,000
1,500
2,000
Minimum
Parti cul ate
120
215
571
4,810
12,566
15,711
27,664
34,131
69,379
107,537
Dilution
Dissolved
39
141
152
200
290
421
617
789
1,425
1,957
*MODEL INPUTS: Water Depth = 5 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Forced Separation.
A-5
-------
TABLE A-6. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 6*
Distance
(m)
15.2
45.7
100.0
137.2
182.9
304.8
609.6
from Discharge
(ft)
50
150
328
450
600
1,000
2,000
Minimum
Parti cul ate
163
391
1,785
3,445
3,964
14,059
78,486
Dilution
Dissolved
52
318
536
755
848
1,445
6,803
*MODEL INPUTS: Water Depth = 10 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Forced Separation.
A-6
-------
TABLE A-7. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 7*
Distance
(m)
15.2
45.7
100.0
137.2
182.9
304.8
609.6
914.4
from Discharge
(ft)
50
150
328
450
600
1,000
2,000
3,000
Minimum
Particulate
71
193
360
678
823
1,919
9,279
30,530
Dilution**
Dissolved
110
176
267
340
437
723
1,708
2,556
*MODEL INPUTS: Water Depth = 10 m
Total Discharge Rate = 1,000 bbl/h
Mud Discharge Rate = 100 bbl/h
Prediction 9:1
Surface Current = 10 cm/sec
Forced Separation.
**Dilutions are due to receiving water only. To obtain total
dilution (to include predilution) multiply all dilutions
by 10.
A-7
-------
TABLE A-8. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 8*
Distance
(m)
15.2
45.7
100.0
137.2
182.9
304.8
609.6
914.4
from Discharge
(ft)
50
150
328
450
600
1,000
2,000
3,000
Minimum
Participate
685
1,871
3,859
6,535
9,152
21,880
113,554
354,054
Dilution
Dissolved
196
2,674
4,049
5,181
6,623
10,989
26,302
39,017
*MODEL INPUTS: Water Depth = 10 m
Discharge Rate = 100 bbl/h
Surface Current = 10 cm/sec
Forced Separation.
A-8
-------
TABLE A-9. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 9*
Distance
(m)
15.2
45.7
100.0
137.2
182.9
304.8
609.6
from Discharge
(ft)
50
150
328
450
600
1,000
2,000
Minimum
Parti cul ate
66
230
299
471
808
1,994
10,809
Dilution
Dissolved
68
110
168
238
290
518
2,483
*MODEL INPUTS: Water Depth = 10 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Bulk Mud Density = 9 Ib/gal
Initial Solids Concentration = 106,900 mg/1
Forced Separation.
A-9
-------
TABLE A-10. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 10*
Distance
(m)
15.2
30.5
61.0
100.0
137.2
182.9
243.8
304.8
365.8
from Discharge
(ft)
50
100
200
328
450
600
800
1,000
1,200
Minimum
Particulate
67
559
3,405
11,407
20,247
36,288
60,142
90,175
131,478
Dilution
Dissolved
61
127
478
1,218
1,930
3,612
5,826
8,547
11,787
*MODEL INPUTS: Water Depth = 15 m
Discharge Rate = 1,000 bbl/h
Surface Current = 2 cm/sec
Forced Separation.
A-10
-------
TABLE A-ll. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 11*
Distance
(m)
15.2
30.5
61.0
100.0
137.2
182.9
243.8
304.8
365.8
426.7
548.7
609.6
from Discharge
(ft)
50
100
200
328
450
600
800
1,000
1,200
1,400
1,800
2,000
Minimum
Particulate
150
197
437
1,748
3,521
4,595
7,741
10,933
14,494
20,875
32,058
40,868
Dilution
Dissolved
72
280
371
526
875
853
1,209
1,460
1 ,905
2,179
3,120
3,458
*MODEL INPUTS: Water Depth = 15 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Forced Separation.
A-ll
-------
TABLE A-12. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 12*
Distance
(m)
15.2
30.5
61.0
100.0
137.2
182.9
243.8
304.8
365.8
426.7
548.7
609.6
from Discharge
(ft)
50
100
200
328
450
600
800
1,000
1,200
1,400
1,800
2,000
Minimum
Participate
186
268
535
752
1,007
2,053
3,979
6,806
9,461
10,264
12,608
18,817
Dilution
Dissolved
68
147
903
1,003
1,142
1,351
1,484
1,869
1,934
2,439
2,688
*MODEL INPUTS: Water Depth = 15 m
Discharge Rate = 1,000 bbl/h
Surface Current = 30 cm/sec
Forced Separation.
A-12
-------
TABLE A-13. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 13*
Distance
(m)
15.2
45.7
100.0
137.2
182.9
304.8
609.6
914.4
from Discharge
(ft)
50
150
328
450
600
1,000
2,000
3,000
Mi nimum
Participate
115
513
1,092
3,289
8,215
40,937
99,379
Dilution
Dissolved
43
682
1,082
1,458
1,587
2,571
10,870
*MODEL INPUTS: Water Depth = 20 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Forced Separation.
A-13
-------
TABLE A-14. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 14*
Distance
(m)
15.2
45.7
100.0
137.2
182.9
304.8
609.6
914.4
from Discharge
(ft)
50
150
328
450
600
1,000
2,000
3,000
Minimum
Participate
333
345
731
1,225
1,618
3,312
19,497
19,071
Dilution
Dissolved
202
797
1,186
1,548
1,835
2,980
13,580
10,412
*MODEL INPUTS: Water Depth = 40 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Minimal stratification [AO (bottom to
surface)] = 0.5.
Forced Separation
A-14
-------
TABLE A-15. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 15*
Distance
(m)
15.2
45.7
100.0
304.8
609.6
914.4
from Discharge
(ft)
50
150
328
1,000
2,000
3,000
Minimum
Particulate
972
1,305
1,803
2,511
11,217
11,697
Dilution
Dissolved
1,547
2,073
2,702
3,625
15,593
14,626
*MODEL INPUTS: Water Depth = 70 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Forced Separation.
A-15
-------
TABLE A-16. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 16*
Distance
(m)
100.0
137.2
182.9
304.8
426.7
548.6
609.6
from Discharge
(ft)
328
450
600
1,000
1,400
1,800
2,000
Minimum
Particulate
1,437
1,695
2,397
5,443
10,892
16,510
23,325
Dilution
Dissolved
2,503
2,700
3,567
7,289
13,567
18,788
25,714
*MODEL INPUTS: Water Depth = 120 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Forced Separation.
A-16
-------
TABLE A-17. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 17*
Distance
(m)
30.5
61.0
100.0
201.2
411.5
1,219.2
1,609.4
2,414.0
from Discharge
(ft)
100
200
328
660
1,350
4,000
5,280
7,920
Minimum
Parti cul ate
2,002
4,189
5,793
10,673
17,130
23,504
30,178
107,058
Dilution
Dissolved
2,859
6,671
9,127
16,661
26,803
37,636
43,889
112,514
*MODEL INPUTS: Water Depth = 120 m
Discharge Rate = 1,000 bbl/h
Surface Current = 32 cm/sec
Forced Separation.
A-17
-------
TABLE A-18. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 18*
Distance
(m)
15.2
30.5
61.0
100.0
137.2
182.9
243.8
304.8
from Discharge
(ft)
50
100
200
328
450
600
800
1,000
Minimum
Participate
149
1,540
1,873
6,109
19.418
20,854
50,704
52,286
Dilution
Dissolved
55
152
613
1,040
1,435
2,101
3,030
3,817
*MODEL INPUTS: Water Depth = 5 m
Discharge Rate = 250 bbl/h
Surface Current = 10 cm/sec
Forced Separation.
A-18
-------
TABLE A-19. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 19*
Distance
(m)
15.2
30.5
61.0
100.0
137.2
182.9
213.4
243.8
274.3
304.8
from Discharge
(ft)
50
100
200
328
450
600
700
800
900
1,000
Minimum
Particulate
345
876
3,333
8,873
16,347
27,448
38,213
50,122
64,330
83,585
Dilution
Dissolved
188
430
1,073
2,239
3,293
4,608
5,798
6,672
8,021
9,415
*MODEL INPUTS: Water Depth = 15 m
Discharge Rate = 250 bbl/h
Surface Current = 2 cm/sec
Forced Separation.
A-19
-------
TABLE A-20. MINIMUM SOLIDS AND DISSOLVED FRACTION DILUTIONS
PREDICTED BY THE OOC MODEL FOR CASE 20*
Distance
(m)
15.2
30.5
61.0
100.0
137.2
182.9
243.8
304.8
365.8
from Discharge
(ft)
50
100
200
328
450
600
800
1,000
1,200
Minimum
Particulate
492
1,398
1,544
2,558
4,447
5,259
9,282
13,136
18,406
Dilution
Dissolved
157
468
1,416
2,538
3,115
3,846
4,926
6,098
7,246
*MODEL INPUTS: Water Depth = 15 m
Discharge Rate = 250 bbl/h
Surface Current = 10 cm/sec
Forced Separation.
A-20
-------
APPENDIX B
SOLIDS DEPOSITION AS PREDICTED BY
THE OOC MODEL
-------
TABLE B-l. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 1*
Distance from
Discharge
(m) (ft)
30.5
61.0
91.4
121.9
152.4
182.9
213.4
243.8
274.3
304.8
335.3
365.8
396.2
426.7
457.2
100
200
300
400
500
600
700
800
900
1,000
1,100
1,200
1,300
1,400
1,500
Maximum
Deposition
(g/m2)
4,482
1,113
395
195
127
132
112
103
93
83
73
68
59
45
32
Maximum**
Thickness of
Deposited Mud
(cm)
0.180
0.045
0.016
0.008
0.005
0.005
0.004
0.004
0.004
0.003
0.003
0.003
0.002
0.002
0.001
Cumulative***
Percent of
Deposited
Solids
63
78
84
86
88
90
92
93
94
95
96
97
98
99
99
*MODEL INPUTS: Water Depth = 40 m
Total Discharge Rate = 1,000 bbl/h
Mud Discharge Rate = 100 bbl/h
Prediction 9:1
Surface Current = 2 cm/sec
Total Solids Discharge = 22,907 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm3.
***After 24,000 sec (400 min).
B-l
-------
TABLE B-2. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 2i
Distance from
Discharge
(m) (ft)
30.5
61.0
91.4
121.9
152.4
182.9
213.4
243.8
274.3
304.8
365.8
426.7
487.7
548.6
609.6
100
200
300
400
500
600
700
800
900
1,000
1,200
1,400
1,600
1,800
2,000
Maximum
Deposition ,
(g/m2)
1,343
33
54
137
83
78
59
63
63
73
98
41
19
18
16
Maximum**
Thickness of
Deposited Mud
(cm)
0.054
0.001
0.002
0.005
0.003
0.003
0.002
0.003
0.003
0.003
0.003
0.002
0.001
0.001
0.001
Cumulative***
Percent of
Deposited
Solids
57
59
61
67
70
74
76
79
82
85
92
96
98
MOO
*MODEL INPUTS: Water Depth = 40 m
Total Discharge Rate = 1,000 bbl/h
Mud Discharge Rate = 100 bbl/h
Predilution 9:1
Surface Current = 10 cm/sec
Total Solids Discharge = 22,925 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm3.
***After 10,000 sec (167 min).
B-2
-------
TABLE B-3. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 3*
Distance from
Discharge
(m) (ft)
30.5
61.0
91.4
121.9
152.4
182.9
213.4
243.8
274.3
304.8
365.8
426.7
487.7
548.6
609.6
670.6
731.5
762.0
100
200
300
400
500
600
700
800
900
1,000
1,200
1,400
1,600
1,800
2,000
2,200
2,400
2,500
Maximum
Deposition
(kg/m2)
15.2
21.9
13.4
9.9
3.8
2.7
1.6
1.1
0.8
0.6
0.4
0.4
0.3
0.3
0.2
0.2
0.2
0.1
Maximum**
Thickness of
Deposited Mud
(cm)
0.609
0.877
0.535
0.398
0.150
0.109
0.062
0.045
0.033
0.023
0.015
0.015
0.012
0.011
0.009
0.007
0.006
0.006
Cumulative***
Percent of
Deposited
Solids
20
49
67
80
85
89
91
92
93
94
95
96
97
98
99
99
99
MOO
*MODEL INPUTS: Water Depth = 40 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Total Solids Discharge = 114,621 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm^.
***After 10,000 sec (167 min).
B-3
-------
TABLE B-4. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 4*
Distance
from Maximum
Discharge Deposition
(m) (ft) (g/m2)
30.5
61.0
91.4
121.9
152.4
182.9
213.4
243.8
274.3
304.8
335.3
365.8
396.2
426.7
457.2
487.7
*MODEL INPUTS:
100 1,546
200 132
* 300 59
400 54
500 112
600 98
700 63
800 32
900 43
1,000 59
1,100 132
1,200 88
1,300 48
1,400 22
1,500 12
1,600 12
Water Depth = 40 m
Discharge Rate = 100
Surface Current = 10
Maximum**
Thickness of
Deposited Mud
(cm)
0.062
0.005
0.002
0.002
0.004
0.004
0.003
0.001
0.002
0.002
0.005
0.004
0.002
0.001
^0.000
bbl/h
cm/sec
Cumulative***
Percent of
Deposited
Solids
58
63
65
67
71
75
77
79
80
82
87
91
92
93
94
94
Total Solids Discharge = 22,927 kg
**Assuming an
***flftar in nn
Forced Separation.
in-place density of 2.5
n <-a/- / i C7 m-; - \
g/cm^.
B-4
-------
TABLE B-5. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 5*
Distance from
Discharge
(m) (ft)
15.2
30.5
45.7
61.0
76.2
91.4
106.7
121.9
137.2
152.4
182.9
213.4
243.8
274.3
304.8
50
100
150
200
250
300
350
400
450
500
600
700
800
900
1,000
Maximum
Deposition
(kg/m2)
439.00
27.00
7.80
6.10
5.50
1.30
0.60
0.50
0.30
0.30
0.06
0.08
0.04
0.04
0.02
Maximum**
Thickness of
Deposited Mud
(cm)
17.600
1.100
0.312
0.242
0.219
0.051
0.023
0.019
0.012
0.011
0.002
0.003
0.002
0.002
0.001
Cumulative***
Percent of
Deposited
Solids
90
95
97
98
99
99
MOO
*MODEL INPUTS: Water Depth = 5 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Total Solids Discharge = 114,586 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm^.
***After 10,000 sec (167 min).
B-5
-------
TABLE B-6. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 6*
Distance from
Discharge
(m) (ft)
15.2
30.5
45.7
61.0
76.2
91.4
106.7
121.9
137.2
152.4
167.6
182.9
198.1
213.4
228.6
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
Maximum
Deposition
(kg/m2)
168.0
254.0
21.0
6.6
3.9
2.7
2.7
2.7
2.2
1.3
1.0
0.5
0.2
0.1
0.1
Maximum**
Thickness of
Deposited Mud
(cm)
6.70
10.20
0.86
0.27
0.16
0.11
0.11
0.11
0.09
0.05
0.04
0.02
0.01
0.01
^0.00
Cumulative***
Percent of
Deposited
Solids
36
90
95
96
97
97
98
99
99
99
MOO
*MODEL INPUTS: Water Depth = 10 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Total Solids Discharge = 114,567 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm3.
***After 8,000 sec (133 min).
B-6
-------
TABLE B-7. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 7*
Distance from
Discharge
(m) (ft)
15.2
30.5
45.7
61.0
76.2
91.4
106.7
121.9
137.2
152.4
182.9
213.4
243.8
274.3
304.8
50
100
150
200
250
300
350
400
450
500
600
700
800
900
1,000
Maximum
Deposition
(kg/m2)
27.0
26.0
8.6
13.0
5.1
1.4
0.9
0.9
0.9
0.8
0.2
0.2
0.2
0.2
0.1
Maximum**
Thickness of
Deposited Mud
(cm)
1.078
1.031
0.344
0.508
0.203
0.057
0.035
0.035
0.034
0.032
0.009
0.008
0.009
0.006
0.004
Cumulative***
Percent of
Deposited
Solids
31
60
70
84
90
92
93
94
95
96
97
97
98
98
98
*MODEL INPUTS: Water Depth = 10 m
Total Discharge Rate = 1,000 bbl/h
Mud Discharge Rate = 100 bbl/h
Predilution 9:1
Surface Current = 10 cm/sec
Total Solids Discharge = 22,898 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm3.
***After 10,000 sec (167 min).
B-7
-------
TABLE B-8. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 8*
Distance fr
Discharge
(m)
15.2
30.5
45.7
61. U
76.2
91.4
106.7
121.9
137.2
152.4
182.9
213.4
243.8
274.3
304.8 1
om
(ft)
50
100
150
200
250
300
350
400
450
50U
600
700
800
900
,000
Maximum
Deposition
(kg/m2)
28.0
27.0
14.0
8.2
3.1
0.9
1.1
0.9
0.8
0.7
0.2
0.2
0.2
0.1
0.1
Maximum**
Thickness of
Deposited Mud
(cm)
1.140
1.078
0.570
0.328
0.125
0.037
0.042
0.035
0.031
0.027
0.009
0.008
0.007
0.005
0.005
Cumulative***
Percent of
Deposited
Solids
32
63
79
88
92
93
94
95
96
96
97
98
98
98
99
*MODEL INPUTS: Water Depth = 10 m
Discharge Rate = 100 bbl/h
Surface Current = 10 cm/sec
Total Solids Discharge = 22,901 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm3.
***After 10,000 sec (167 min).
B-8
-------
TABLE B-9. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 9*
Distance from
Discharge
(m) (ft)
15.2
30.5
45.7
61.0
76.2
91.4
106.7
121.9
137.2
152.4
182.9
213.4
243.8
274.3
304.8
50
100
150
200
250
300
350
400
450
500
600
700
800
900
1,000
Maximum
Deposition
(kg/m2)
8.10
10.40
4.20
1.70
1.40
1.60
1.40
0.60
0.30
0.10
0.10
0.10
0.09
0.08
0.10
Maximum**
Thickness of
Deposited Mud
(cm)
0.323
0.417
0.166
0.066
0.055
0.064
0.057
0.025
0.012
0.005
0.005
0.006
0.004
0.003
0.004
Cumulati ve***
Percent of
Deposited
Solids
25
58
71
77
81
86
90
92
93
94
95
96
96
97
97
*MODEL INPUTS: Water Depth = 10 m
Discharge Rate = 1,000 bbl/h
Bulk Mud Density = 9 Ib/gal
Surface Current = 10 cm/sec
Total Solids Discharge = 8,505 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm^.
***After 8,000 sec (133 min).
B-9
-------
TABLE B-10. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE
Distance fr
Discharge
(m)
15.2
30.5
45.7
61.0
76.2
91.4
106.7
121.9
137.2
152.4
182.9
213.4
243.8
274.3
304.8 1
335.3 1
365.8 1
om
(ft)
50
100
150
200
250
300
350
400
450
500
600
700
800
900
,000
,100
,200
Maximum
Deposition
(kg/m2)
129.00
221.00
25.00
1.10
0.40
0.30
0.20
0.20
0.20
0.10
0.10
0.10
0.08
0.06
0.06
0.04
0.02
Maximum**
Thickness of
Deposited Mud
(cm)
5.200
8.800
1.000
0.044
0.016
0.012
0.008
0.008
0.008
0.004
0.004
0.004
0.003
0.002
0.002
0.002
0.001
Cumulative***
Percent of
Deposited
Solids.
34
92
99
99
99
MOO
*MODEL INPUTS: Water Depth = 15 m
Discharge Rate = 1,000 bbl/h
Surface Current = 2 cm/sec
Total Solids Discharge = 114,433 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm^.
***After 20,000 sec (333 min).
B-10
-------
TABLE B-ll. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 11*
Distance from
Discharge
On) (ft)
15.2
30.5
45.7
61.0
76.2
91.4
106.7
121.9
137.2
152.4
182.9
213.4
243.8
274.3
304.8
50
100
150
200
250
300
350
400
450
500
600
700
800
900
1,000
Maximum
Deposition
(kg/m2)
76.0
159.0
105.0
15.0
5.1
7.4
5.1
2.0
0.8
0.4
0.3
0.2
0.1
0.1
0.1
Maximum**
Thickness of
Deposited Mud
(cm)
3.031
6.358
4.218
0.568
0.203
0.297
0.203
0.078
0.033
0.017
0.011
0.007
0.004
0.004
0.004
Cumulati ve***
Percent of
Deposited
Solids
20
62
90
93
95
97
98
99
99
99
99
99
99
99
99
*MODEL INPUTS: Water Depth = 15 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Total Solids Discharge = 114,555 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm^.
***After 10,000 sec (167 min).
B-ll
-------
TABLE B-12. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 12*
Distance from
Discharge
(m) (ft)
30.5
61.0
91.4
121.9
152.4
182.9
213.4
243.8
274.3
304.8
365.8
426.7
487.7
548.6
609.6
100
200
300
400
500
600
700
800
900
1,000
1,200
1,400
1,600
1,800
2,000
Maximum
Deposition
(kg/m2)
28.00
48.00
30.00
4.50
1.40
0.80
1.30
1.00
0.70
0.50
0.20
0.08
0.05
0.05
0.05
Maximum**
Thickness of
Deposited Mud
(cm)
0.953
1.925
1.197
0.180
0.057
0.031
0.051
0.039
0.027
0.021
0.008
0.003
0.002
0.002
0.002
Cumulative***
Percent of
Deposited
Solids
21
63
89
93
94
95
96
97
97
98
98
99
99
99
99
*MODEL INPUTS: Water Depth = 15 m
Discharge Rate = 1,000 bbl/h
Surface Current = 30 cm/sec
Total Solids Discharge = 114,556 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm3.
***After 10,000 sec (167 min).
B-12
-------
TABLE B-13. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 13*
Distance from
Discharge
(m) (ft)
30.5
61.0
91.4
121.9
152.4
182.9
213.4
243.8
274.3
304.8
335.3
365.8
396.2
426.7
457.2
100
200
300
400
500
600
700
800
900
1,000
1,100
1,200
1,300
1,400
1,500
Maximum
Deposition
(kg/m2)
55.00
43.00
5.40
3.00
1.90
0.70
0.40
0.30
0.20
0.20
0.20
0.10
0.09
0.09
0.08
Maximum**
Thickness of
Deposited Mud
(cm)
2.210
1.740
0.210
0.121
0.074
0.027
0.016
0.012
0.008
0.006
0.006
0.005
0.004
0.004
0.003
Cumulative***
Percent of
Deposited
Solids
49
88
93
96
97
98
98
99
99
99
99
99
99
99
MOO
*MODEL INPUTS: Water Depth = 20 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Total Solids Discharge = 114,551 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm^.
***After 10,000 sec (167 min).
B-13
-------
TABLE B-14. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 14*
Distance fr
Discharge
(m)
30.5
61.0
91.4
121.9
152.4
182.9
213.4
243.8
274.3
304.8 1
365.8 1
426.7 1
487.7 1
548.6 1
609.6 2
670.6 2
731.5 2
om
(ft)
100
200
300
400
500
600
700
800
900
,000
,200
,400
,600
,800
,000
,200
,400
Maximum
Deposition
(kg/m2)
. 16.2
35.2
12.9
6.7
2.8
1.5
0.8
0.4
0.4
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
Maximum**
Thickness of
Deposited Mud
(cm)
0.646
1.410
0.517
0.269
0.113
0.060
0.031
0.018
0.014
0.010
0.007
0.006
0.007
0.006
0.004
0.003
0.003
Cumulative***
Percent of
Deposited
Solids
20
65
81
89
93
95
96
96
97
97
98
98
98
99
99
99
'-100
*MODEL INPUTS:
Water Depth = 40 m
Discharge Rate = 1,000 bbl/h
Minimum Stratification (Aot surface to bottom)
Surface Current = 10 cm/sec
Total Solids Discharge = 114,539 kg
Forced Separation.
= 0.5
**Assuming an in-place density of 2.5 g/cm3.
***After 10,000 sec (167 min).
B-14
-------
TABLE B-15. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 15*
Distance from
Discharge
(m) (ft)
61.0
121.9
182.9
243.8
304.8
365.8
426.7
487.7
548.6
609.6
670.6
731.5
792.5
853.5
914.4
200
400
600
800
1,000
1,200
1,400
1,600
1,800
2,000
2,200
2,400
2,600
2,800
3,000
Maximum
Deposition
(g/m2)
878
603
410
264
238
249
143
187
181
143
114
105
111
115
100
Maximum**
Thickness of
Deposited Mud
(cm)
0.035
0.024
0.016
0.011
0.010
0.010
0.006
0.007
0.007
0.006
0.005
0.004
0.004
0.005
0.004
Cumul ati ve***
Percent of
Deposited
Solids
20
33
42
48
53
59
62
66
70
74
76
78
81
83
86
*MODEL INPUTS: Water Depth = 70 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Total Solids Discharge = 114,634 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm^.
***After 14,000 sec (233 min).
B-15
-------
TABLE B-16. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 16*
Distance from
Discharge
(m) (ft)
61.0
121.9
182.9
243.8
304.8
365.8
426.7
487.7
548.6
609.6
731.5
853.5
975.4
1,097.3
200
400
600
800
1,000
1,200
1,400
1,600
1,800
2,000
2,400
2,800
3,200
3,600
Maximum
Deposition
(g/m2)
330
1,001
3,015
647
415
354
317
305
244
195
146
134
74
12
Maximum**
Thickness of
Deposited Mud
(cm)
0.013
0.040
0.121
0.026
0.017
0.014
0.013
0.012
0.010
0.008
0.006
0.005
0.003
^0.000
Cumulative***
Percent of
Deposited
Solids
4
17
57
65
71
75
80
84
87
89
93
97
99
MOO
*MODEL INPUTS: Water Depth = 120 m
Discharge Rate = 1,000 bbl/h
Surface Current = 10 cm/sec
Total Solids Discharge = 114,554 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm3.
***After 16,000 sec (267 min).
B-16
-------
TABLE B-17. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 17*
Distance from
Discharge
(m) (ft)
152.4
304.8
457.2
609.6
762.0
914.4
1,066.8
1,219.2
1,371.6
1,524.0
1,676.4
1,828.8
2,133.6
2,438.4
2,743.2
3,048.0
3,200.4
3,352.8
3,657.6
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
5,500
6,000
7,000
8,000
9,000
10,000
10,500
11,000
12,000
Maximum
Deposition
(g/m2)
0.0
0.0
0.0
0.1
1.4
5.8
17.0
14.0
4.3
1.3
1.3
1.8
6.4
21.0
41.0
51.0
63.0
37.0
3.5
Maximum**
Thickness of
Deposited Mud
(cm)
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.001
0.000
0.000
0.000
0.000
0.000
0.001
0.002
0.002
0.003
0.001
^0.000
Cumulati ve***
Percent of
Deposited
Solids
0
0
0
0
0
2
6
10
11
11
12
12
15
23
43
67
84
93
MOO
*MODEL INPUTS: Water Depth = 120 m
Discharge Rate = 1,000 bbl/h
Surface Current = 32 cm/sec
Total Solids Discharge = 114,646 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm3.
***After 16,000 sec (267 min).
B-17
-------
TABLE B-18. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 18*
Distance from
Di
(m)
15.2
30.5
45.7
61.0
76.2
91.4
106.7
121.9
137.2
152.4
182.9
213.4
243.8
274.3
304.8
scharge
(ft)
50
100
150
200
250
300
350
400
450
500
600
700
800
900
1,000
Maximum
Deposition
(kg/m?)
352.00
105.00
10.00
8.00
5.00
1.00
1.00
0.70
0.60
0.40
0.20
0.10
0.08
0.06
0.04
Maximum**
Thickness of
Deposited Mud
(cm)
14.100
4.200
0.400
0.300
0.200
0.060
0.040
0.030
0.020
0.020
0.010
0.004
0.003
0.002
0.002
Cumulati ve***
Percent of
Deposited
Solids
72
94
96
98
99
99
99
99
99
^100
*MODEL INPUTS: Water Depth = 5 m
Discharge Rate = 250 bbl/h
Surface Current = 10 cm/sec
Total Solids Discharge = 114,652 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm3.
***After 10,000 sec (167 min).
B-18
-------
TABLE B-19. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 19*
Distance from
Discharge
On) (ft)
15.2
30.5
45.7
61.0
76.2
91.4
106.7
121.9
137.2
152.4
182.9
213.4
243.8
50
100
150
200
250
300
350
400
450
500
600
700
800
Maximum
Deposition
(kg/m2)
131.00
195.00
33.00
4.30
1.40
0.80
0.60
0.40
0.30
0.30
0.20
0.10
0.06
Maximum**
Thickness of
Deposited Mud
(cm)
5.200
7.800
1.300
0.200
0.060
0.030
0.020
0.020
0.010
0.010
0.010
0.004
0.002
Cumulative***
Percent of
Deposited
Solids
36
89
98
99
99
99
MOO
*MODEL INPUTS: Water Depth = 15 m
Discharge Rate = 250 bbl/h
Surface Current = 2 cm/sec
Total Solids Discharge = 114,652 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm^.
***After 16,000 sec (267 min).
B-19
-------
TABLE B-20. SOLIDS DEPOSITION FROM OOC MODEL FOR CASE 20*
Distance from
Discharge
(m) (ft)
15.2
30.5
45.7
61.0
76.2
91.4
106.7
121.9
137.2
152.4
182.9
213.4
243.8
274.3
304.8
50
100
150
200
250
300
350
400
450
500
600
700
800
900
1,000
Maximum
Deposition
(kg/m2)
67.0
92.0
69.0
71.0
25.0
6.0
6.0
7.0
6.0
4.0
2.0
1.0
0.6
0.5
0.3
Maximum**
Thickness of
Deposited Mud
(cm)
2.70
3.70
2.80
2.80
1.00
0.20
0.20
0.30
0.20
0.20
0.06
0.03
0.02
0.02
0.01
Cumulati ve***
Percent of
Deposited
Solids
18
43
62
82
88
90
92
94
95
96
97
98
98
99
99
*MODEL INPUTS: Water Depth = 15 m
Discharge Rate = 250 bbl/h
Surface Current = 10 cm/sec
Total Solids Discharge = 114,652 kg
Forced Separation.
**Assuming an in-place density of 2.5 g/cm3.
***After 10,000 sec (167 min).
B-20
-------
APPENDIX C
FIELD OBSERVATIONS OF DRILLING MUD DILUTION
-------
SUMMARY OF FIELD OBSERVATIONS OF DRILLING MUD DILUTION
SHALLOW WATER STUDIES
Northern Technical Services (1981, pp. 70-92) conducted two shallow
water effluent disposal studies off Reindeer Island in the Beaufort Sea
at locations shown in Figure C-l. A summary of the discharge conditions
and effluent characteristics for both tests is given in Table C-l. Drilling
effluent was mixed with Rhodamine WT dye and then discharged vertically
through the sea ice from a 7.6 cm (3 in) diameter nozzle at Reynolds numbers
ranging from 103 to 105 (Northern Technical Services 1981, p. 99). Dye
concentrations were measured throughout the water column through augered
holes along transects running parallel or perpendicular to the principal
current direction. Water temperature and salinity profiles taken on April 20
showed a vertical density gradient of approximately 8xlO~5 g/cm-3 change
per meter (density decreasing with depth). Profiles taken earlier (April
17 and 18) showed that density decreased slightly to 4.5 m (15 ft.) depth
and then increased with depth to the seafloor.
Results indicated that the effluent formed a circular jet which spread
radially outward as a wall jet when it contacted the seafloor. Dye concen-
trations were not detected until a distance of 10 m (33 ft) from the discharge
point for test case 2 and 50 to 60 m (164 to 197 ft) for test case 1 (Northern
Technical Services 1981, p. 85). At distances less than these detection
points, the height of rise of the wall jet above the seafloor was less
than 0.5 m (1.6 ft). Because of sampling string configuration, it was
not possible to monitor conditions within 0.5 m (1.6 ft) of the seafloor.
As the wall jet expanded radially outward, it moved with the mean laminar
current flow.
For test plot 1, current data indicated that velocities were less
than the threshold of the meter [1.5 cm/sec (0.05 ft/sec)]. A higher discharge
C-l
-------
US'DO1
US'701
UB'10'
IIST WELL-
TEST PLOT 10-WIND SENSOR
JULY. 1979)
BEAUFORT SEA
TEST PLOT t - DEEP WATER
BELOW ICE DISPOSAL SITE
TEST PLOT 3 - DEEP
WATEB CONTROL LOCATION
TEST PLOT 2-SHALLOW WATER
BELOW ICE DISPOSAL SITE '
TEST PLOT I - WIND SENSOB
(APRIL-MAT. 1979)
TEST PLOT 5 - SHALLOW
WA'ER CONTROL LOCATION
NIAKUK 3 WELL
v\ r^s n.
NOTE CUBBENT METERS AT TEST PIOTS I AND 1 ,r\
KSS it $\
7C*
REFERENCE: Nortec, 1981
Figure C-l. Location map of test plots for the below-ice
disposal studies (Reindeer Island).
C-2
-------
TABLE C-l. SUMMARY OF DISCHARGE CONDITIONS AND PHYSICAL
CHARACTERISTICS OF DRILLING EFFLUENTS USED IN
THE BELOW-ICE TEST DISCHARGES AT REINDEER ISLAND
Location
Test Plot 1
Test Plot 2
Date of test
Time of discharge
Test fluid
Volume discharged
Discharge rate
Discharge hose diameter
Discharge temperature
Density (at 20° C)
Ice thickness
Water depth
Depth below discharge point
Average current speed
Depth of current meter
Discharge Reynolds number
April 30, 1979
1854-1858 AST
Drill ing mud
16.0xig3 1 (100 bbl)
4.0xl03 1pm (1,510 bbl/h)
7.6 cm
23° c
1.16 g/ml
1.8 m
8.4 m
7.6 m
<1.5 cm/sec
6.7 m
7.5xl05
April 22, 1979
1730-2030 AST
Reserve pit fluids
9.5xl03 1 (60 bbl)
5.7X101 1pm (21 bbl/h)
7.6 cm
19° c
1.05 g/ml
1.9 m
5.5 m
5.3 m
4.4 cm/sec
4.0 m
1.3xl03
C-3
-------
rate (1,500 bbl/h) and larger volume of mud (100 bbl) was discharged at
this site than at test plot 2. Ambient conditions included water temper-
atures from -1.24 to -1.23° C and salinities from 32.26 to 32.44 ppt (Northern
Technical Services 1981, p. 82). Minimum dilutions and percent transmittance
for test plot 1 monitoring are shown in Table C-2. Results from this test
plot do not follow expected plume behavior. Dye concentration increased
with increasing distance from the discharge point and it is probable that
the effluent plume was not sampled in several locations. Transmittance
measurements indicated that separation of dye from suspended solids occurred
before a distinct plume was observed in the water column [50 to 60 m (164
to 197 ft) from the discharge] (Northern Technical Services 1981, p. 85).
Transmittance increased to ambient levels at 244 m (800 ft) downcurrent
indicating that a majority of solids had been deposited within this distance.
Results of the measurements for test plot 2 are shown in Table C-3.
Ambient sea water conditions for this case included water temperatures
of approximately -1.28° C and salinities from 32.93 to 33.04 ppt. Dye
concentration generally decreases with distance from the discharge. Trans-
mittance indicates that there was some separation of solids from the dye
plume during the study. It is assumed that the effluent plume was not
captured in samples taken for distances of 1.5, 6.1, 30.5, and 61 m (5,
20, 100, and 200 ft). Results from test plot 2 were used to formulate
an empirical relationship between concentration and distance from discharge.
Both of these studies measure the dilution of the dissolved fraction.
Although the dissolved and solid fractions are related, the dilution of
the dye will not accurately represent the solids dilution if separation
of the two plumes occurs.
Northern Technical Services (1983, pp. 9-60) conducted another drilling
effluent disposal study in the Beaufort Sea, Alaska (Tern Island). Case 1
conditions included a mud discharge rate of 84 bbl/h, a predilution of
30:1 with seawater and an average current velocity of 12 cm/sec (0.5 ft/sec)
at 3.4 m (11 ft) above the seafloor. Case 2 conditions included a mud
discharge rate of 34 bbl/h, predilution of 75:1 with seawater and an average
C-4
-------
TABLE C-2. BELOW-ICE EFFLUENT DISCHARGE DILUTION FROM
TEST PLOT 1 (8.4 m DEPTH)*, REINDEER ISLAND
Distance
(m)
12.2
18.3
30.5
61.0
122.0
244.0
Ambient
Depth of
Observation (m)
7.0
7.0
7.0
6.0
6.1-5.7
5.9-6.1
2.0-7.5
Minimum
Transmittance (%}
84
80
70
85
62-63
82-84
80
Maximum Dye
Concentration
C/Co
5.7xlO-5
1.4xlO-3
1. 7xlO-3
8.9xlO-3
l.lxlO'2
1.2xlO-2
0
Minimum
Dilution
17,544
714
588
112
91
83
a Average current speed of 1.2 cm/sec.
Source: Nortec (1981).
C-5
-------
TABLE C-3. BELOW-ICE EFFLUENT DISCHARGE DILUTION FROM
TEST PLOT 2 (5.5 m DEPTH)*, REINDEER ISLAND
Distance
(m)
1.5
3.0
6.1
12.2
18.3
30.5
61.0
Ambient
Depth of
Observation
(m)
4.9
4.9
2.0-2.2
4.5
3.2-3.4
3.5
2.2-3.5
2.6-5.0
Minimum
Transmittance
m
47
46
48-54
73
51-65
65
46-74
92
Maximum Dye
Concentration
C/Co
7.0xlO-5
1.2xlO-2
5.7xlO'5
3.5X10'3
2.6xlO-3
7.9xlO~5
2.0xlO'6
0
Minimum
Dilution
14,286
83
17,544
286
385
12,658
500,000
a Average current speed of 4.4 cm/sec.
C-6
-------
current of 11 cm/sec (0.36 ft/sec). Both discharges were made from a man-made
gravel island in 6.7 m (22 ft) of water (Northern Technical Services 1983,
P. 27).
Depths or number of measurements were not given so it is difficult
to determine whether the plume was actually measured (profiles were taken
for test 1). Tables C-4 and C-5 show the results for test 1 and test 2,
respectively. Concentrations measured at 0 to 10 m (0 to 33 ft) from the
discharge are well outside the calibration range of the optical turbidity
sensor used to measure these values. Most of the measurements were made
near the surface [0.5 to 1 m (1.6 to 3.3 ft) from the surface]. Profiles
taken during test 1 showed that most of the effluent remained in the upper
layers due, in part, to a thermocline at 4.5 to 5 m (15 to 16 ft) depth
(Northern Technical Services 1983, p. 33). It is more likely that buoyancy
of the effluent plume kept it near the surface. Water temperatures during
the tests ranged from 0.5 to 1.5° c from bottom to surface and salinities
ranged from 26.8 to 24.8 ppt (from test 1 profiles). Results show that
dilutions of 167:1 and 300:1 were reached for test 1 and 2, respectively,
by approximately 100 m (328 ft) downstream and that slightly greater dilutions
are attained for test 2 and the lower discharge rate. Suspended solids
concentrations were within 5 mg/1 of background levels at 1,900 m (6,234 ft)
and 500 m (1,640 ft) for test 1 and 2, respectively (Northern Technical
Services 1983, p. 34). Only farfield measurements of suspended solids
were given for test plot 2. As shown in Table C-5, these measurements
are within typical background levels (less than 20 mg/1). The dilutions
calculated for this test may be significantly higher if the correct ambient
suspended solids concentrations were subtracted from the measured concentra-
tions. It appears that background suspended solids concentrations were
reached at approximately 210 m (689 ft) from the discharge.
Ecomar (1983, pp. 17-79) conducted drilling mud dispersion studies
in Central Norton Sound in water depths of 12 to 13 m (39 to 43 ft). A
total of 1,100 barrels of mud (bulk density of 10.19 Ib/gal) was discharged
at a rate of 1,060 bbl/h at 1 m (3.3 ft) below the surface through a 0.32 m
(12.6 in) diameter pipe. Measured currents ranged from averages of 15 cm/sec
(0.5 ft/sec) near the bottom to 77 cm/sec (0.5 to 2.5 ft/sec at 1 m (3.3 ft)
C-7
-------
TABLE C-4. MAXIMUM DYE AND SUSPENDED SOLIDS CONCENTRATION
FOR TEST ia, TERN ISLAND
Down Stream
Distance
(m)
10
30
60
100
350
480
730
940
1,100
Maximum Concentration
Suspended
Dyeb Solids
(C/Co) (mg/1)
1.72x10-3 964
5.42xlO-4 271
3.59x10-4 153
1.92x10-4 70
18
10
10
7
4
Minimum Di lution
Suspended0
Dye Solids
581 9
1,845 33
2,786 63
5,208 167
d
d
d
d
d
a Predilution of 30:1, discharge rate of 84 bbl/h.
b It is unclear whether Co is the concentration before or after predilution.
c Dilution due to ambient waters only. Background levels of approximately
20 mg/1 have been subtracted from the sample concentrations.
d Background levels reached.
C-8
-------
TABLE C-5. MAXIMUM DYE AND SUSPENDED SOLIDS CONCENTRATIONS
FOR TEST 2a, TERN ISLAND
Maximum Concentration
Downstream
Distance
(m)
160
210
250
305
350
400
600
640
Dye
(C/Co)b
1.99x10-5
1.81x10-5
7.53x10-6
6.21x10-6
7.79x10-6
7.89x10-6
2.09x10-6
5.16x10-6
Suspended
Solids
(mg/1)
10.4
9.3
5.6
5.6
6.8
5.6
4.4
3.2
Mi nimum
Dye
50,251
55,249
132,802
161,031
128,370
126,743
478,469
193,798
Di lution
Suspended
Solids0
320
358
595d
595d
490d
595d
757d
l,042d
a Predilution of 75:1, discharge rate of 34 bbl/h.
b It is unclear whether Co is the concentration before or after predilution.
c Dilution due to ambient waters only. Background levels are typically
less than 20 mg/1 but exact levels are unknown. Dilutions are calculated
without consideration of background concentrations. Actual dilutions should
be higher.
d Background levels probably reached.
C-9
-------
below the surface. Calculated densities showed little variation from bottom
to surface or from station to station, indicating well mixed conditions
(Ecomar 1983, pp. 15, 30, 31, 33, 40). Table C-6 gives the maximum suspended
solids concentrations measured during the test.
Results indicate that measurements made at distances of 100 to 170 m
(328 to 558 ft) did not sample the maximum concentrations in the plume
since measurements at 650 m (2,113 ft) from the discharge record higher
concentrations. Minimum dilution of suspended solids at 100 m (328 ft)
was approximately 10,116:1, however, solids dilution did not consistently
increase with distance from the discharge and a minimum solids dilution
of 2,252:1 was calculated at 650 m (2,133 ft) from the discharge.
A drilling fluid dispersion study was conducted in the Gulf of Mexico
in 23 m (75 ft) of water during the summer of 1978 (Ayers et al. 1980a,
pp. 351-381). Two discharge rates and volumes were considered: 250 barrels
of mud discharged at a rate of 275 bbl/h and 398 barrels of mud were discharged
at a rate of 1,000 bbl/h (Ayers et al. 1980a, p. 352). Currents during
the low rate discharge ranged from a minimum of 1 cm/sec (0.033 ft/sec)
near the bottom to 22 cm/sec (0.72 ft/sec) at 14 m (46 ft) depth. For
the high rate discharge test, currents ranged from 0 cm/sec near the bottom
to 15.8 cm/sec (0.52 ft/sec) at 7 and 14 m (23 and 46 ft) depth. The drilling
mud used in the study was a chrome 1ignosulfonate-clay mud with density
of 2.09 g/cm3 (17.4 Ib/gal). Sampling was conducted at the top, bottom,
and most dense part of the plume using a rosette sampling array deployed
from a helicopter. Ambient water conditions during the 275 bbl/h discharge
included water temperatures from 22° c near the bottom to 30.1° near the
surface and salinities of 34 ppt near bottom to 24.8 ppt near surface.
For the high rate discharge (1,000 bbl/h), temperatures ranged from 34.0
to 24.8 ppt bottom to surface (Ayers et al. 1980a, pp. 363-366).
During both tests, the effluent formed two plumes: a lower plume
which contained a majority of the solids and an upper plume several meters
thick which remained in the water column much longer than the lower plume.
Measurements for these studies were directed toward describing the effect
of the upper plume on water quality.
C-10
-------
TABLE C-6. MAXIMUM SUSPENDED SOLIDS CONCENTRATIONS*
FOR NORTON SOUND STUDY
Distance
Down Stream
(m)
3
6
45
70
100
105
110
150
170
650
690
Depth
Noted
(m)
2
4
4
1
10
11
12
6
1
13
2
Maximum
Suspended
Solids
(mg/1 )
2,640
1,210
116
201
75
68
92
67
88
194
90
Minimum"
Dilution
117
262
5,388
2,140
10,116
37,718
9,429
43,106
10,776
2,252
10,058
a Ambient suspended solids concentrations average 60 mg/1.
b Assuming a whole mud concentration of 301,740 mg/1. Background levels
have been subtracted from sample concentrations before calculating minimum
dilution.
C-ll
-------
Table C-7 shows the maximum measured suspended solids concentrations
for both discharge rates. Results indicate that greater dilutions were
achieved for the low discharge rate although currents during the high discharge
rate test were slightly less than those during the low rate case. No measure-
ments at 100 m (328 ft) were available for these tests. Dilutions at 100 m
(328 ft) should be greater than those measured at 45 m (148 ft) and 51 m
(167 ft), however.
DEEP UATER STUDIES
Houghton et al. (1980, pp. 285-308) conducted three tests in Lower
Cook Inlet to evaluate the dispersion of drilling effluents in the receiving
water. All tests were conducted in 62 m (203 ft) of water with current
velocities ranging from 31 to 144 cm/sec (1.0 to 4.7 ft/sec) and discharge
rates from 20 to 1,200 bbl/h. Total volumes of mud discharged were very
small ranging from 15 to 47 bbl and duration of discharge ranged from a
few minutes to 2.5 hours. Salinity and temperature profiles taken at the
site indicated little stratification (Houghton et al. 1980, pp. 294-298).
Results from the three tests are shown in Tables C-8 through C-10.
All of these tests measured dilution of the dissolved fraction (dye).
Although the dissolved fractions are related, the dilution of the dye will
not accurately represent the solids dilution if separation of the two plumes
occur. Generally, the minimum dilution increased with distance from the
discharge in all three tests. There was fluctuation in the magnitude of
dilution beginning at approximately 2,600 m (8,530 ft) for test 2 and 2,100 m
(6,890 ft) for test 3, however, all dilutions were on the order of 100,000:1
at these distances. High dilutions were obtained at 1,000 m (3,281 ft)
(on the order of 40,000 to 100,000:1). Only test 1 measured dilutions
at 100 m (328 ft) with a minimum dilution of 38,000:1.
Ayers et al . (1980b, pp. 382-418) conducted drilling mud dispersion
tests in the mid-Atlantic at a site 156 km east of Atlantic City, New Jersey,
in 120 m (394 ft) of water. Two tests were conducted: approximately 500 bbl
of mud were discharged at 500 bbl/h and 220 bbl of mud were released at
C-12
-------
TABLE C-7. MAXIMUM SUSPENDED SOLIDS CONCENTRATIONS AND MINIMUM
DILUTIONS FOR DRILLING MUDS DISCHARGED
TO THE GULF OF MEXICO3
Low Rate Discharge - 275 bbl/h
Distance from
Discharge (m)
6
45
138
250
364
625
Depth
Noted (m)
8
11
9
9
9
9
Solids
Concentration
(mg/1)
14,800
34
8.5
7.0
1.2
0.9
Minimum
Dilution
97
42,060
168,235
242,373
c
c
High Rate Discharge - 1,000 bbl/h
Distance from
Discharge (m)
45
51
152
375
498
777
858
957
1,470
1,550
Depth
Noted (m)
11
12
11
16
14
13
2
12
11
9
Solids
Concentration
(mg/1)
855
727
50.5
24.1
8.6
4.1
1.2
0.83
2.2
1.1
Minimum
Dilution
1,673
1,967
28,890
61,905
188,158
461,290
c
c
c
c
a Suspended solids concentration of whole mud is 1,430,000 mg/1.
b Ambient suspended solids levels are 0.3 to 1.9 mg/1 for the low discharge
rate and 0.4 to 1.1 mg/1 for the high rate.
c Background levels are reached.
C-13
-------
TABLE C-8. SUMMARY OF RESULTS FROM TEST 1, LOWER COOK INLEP
o
I
-t>
Distance from
Discharge (m)
100
200
400
Depth (m)
1
1-7
1-15
Current
Velocity (knots)
2.40
2.65-2.72
2.38-2.63
Maximum Dye
Concentration (ppb)
3.0
1.1
0.8
Minumum
Dilution
38,000
104,000
143,000
a Test Conditions:
Total Volume Discharged = 47 bbl
Initial Dye Concentration = 114,000 ppb
Initial Suspended Solids Concentration = 20,000 mg/1
Duration of Discharge = 140 min.
-------
TABLE C-9. SUMMARY OF RESULTS FROM TEST 2, LOWER COOK INLET3
I
>
en
Distance from
Discharge (m)
940
1,370
1,670
1,980
2,670
4,000
4,830
5,700
6,280
6,370
Depth (m)
1
1
1
7
15
30
15
7
7
15
Current
Velocity (knots)
1.89
1.89
1.90
1.91
1.92
1.44
1.14
0.80
0.60
0.76
Maximum Dye
Concentration (ppb)
3.6
3.3
2.1
1.4
1.3
0.1
0.8
0.6
0.3
0.7
Minumum
Dilution
46,000
53,000
79,000
119,000
128,000
1,660,000
208,000
277,000
553,000
237,000
3 Test Conditions:
Total Volume Discharged = 15 bbl
Initial Dye Concentration = 166,000 ppb
Initial Suspended Solids Concentration = 103,000 mg/1
Duration of Discharge = 5 min.
-------
TABLE C-10. SUMMARY OF RESULTS FROM TEST 3, LOWER COOK INLETa
o
Distance from
Discharge (m)
830
1,760
2,190
5,740
6,480
7,500
9,630
10,930
11,670
13,150
Depth (m)
1
1
7
15
7
1
30
15
7
1
Current
Velocity (knots)
2.05
2.10
2.23
2.35
2.35
2.07
1.92
1.93
1.57
1.52
Maximum Dye
Concentration (ppb)
9.1
1.9
2.7
0.3
1.5
0.5
0.0
0.4
0.3
0.1
Mi numum
Dilution
22,000
107,000
752,000
677,000
135,000
406,000
-
508,000
677,000
203,000
a Test Conditions:
Total Volume Discharged = 40 bbl
Initial Dye Concentration = 203,000 ppb
Initial Suspended Solids Concentration = 700,000 mg/1
Duration of Discharge = 2 min.
-------
275 bbl/h. The mud was discharged at at constant rate and shunted to 12 m
(39 ft) below the water surface. Oceanographic conditions during the tests
included a predominant current to the south and southwest at speeds of
26.9 cm/sec and 21.5 cm/sec [at 10 m (33 ft) depth] for the low rate and
nigh rate discharge tests, respectively (Ayers et al . 1980b, pp. 383, 385,
387). During both tests two plumes formed; a lower plume containing the
bulk of the solids and an upper plume. The upper plume was sampled in
the tests.
Results of the two tests are shown on Tables C-ll and C-12. Generally,
the dilution increases with distance from the discharge. It appears that
the plume may not have been sampled at 15 m (49 ft) from the source. Minimum
dilutions at 100 m (328 ft) varied from approximately 61,000 to 86,000:1
for the high and low rate discharge tests, respectively.
Ray and Meek (1980, pp. 223-258) conducted drill muds and cuttings
discharge monitoring from a semi submersibl e drilling platform on Tanner
Bank (off southern California) in 63 m (207 ft) of water. Mud discharge
rates varied from 10 to 754 bbl/h. Currents showed a predominant southeasterly
flow averaging 21 cm/sec (0.7 ft/sec) (Ray and Meek 1980, p. 223).
Results of these tests are shown in Table C-13. All tests showed
a very high dilution within 100 m (328 ft) of the discharge (on the order
of 100,000:1) and that background suspended solids concentrations were
approached at 200 m (656 ft). One reason for the large dilutions observed
is a phenomenon called "standpipe pumping" (Ray and Meek 1980, p. 226).
As waves pass the rig, they create a large surge of water in and out of
the pipe resulting in increased initial dilutions.
C-17
-------
TABLE C-ll. SUMMARY OF MINIMUM DILUTIONS FOR DRILLING MUDS
DISCHARGED TO THE MID-ATLANTIC - LOW RATE DISCHARGE (275 bbl/h)a
Distance from
Source (m)
0
5
15
73
89
93
97
192
590
701
Depth (m)
12
12
14
14
14
10
23
16
7
7
Suspended Solids
Concentration (mg/1 )
1,398
56
122
12.5
9.7
5.2
4.2
3.5
0.4
1.3
Mi numum
Dilution13
199
5,044
2,293
24,122
31,885
66,048
86,687
110,960
c
924,667
a Test Conditions:
Total Volume Discharged = 220 bbl
Initial Dye Concentration = 277,400 ppb
Background Suspended Solids = 0.1-1.6 mg/1
Bulk Density = 1.21 g/cm3
Dilutions are calculated using a modified solids concentration obtained
by subtracting the ambient suspended solids concentration (assume an average
of 1.0 mg/1) from the measured concentration.
c Background levels reached.
C-18
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TABLE C-12. SUMMARY OF MINIMUM DILUTIONS FOR DRILLING MUDS
DISCHARGED TO THE MID-ATLANTIC - HIGH RATE DISCHARGE (500 bbl/h)*
Distance from
Source (m)
0
5
15
119
149
193
332
352
Depth (m)
14
12
24
10
1
3
1
1
Suspended Solids
Concentration (mg/1 )
100,400
82
1,195
5.1
4.9
4.6
1.8
1.0
Mi numum
Dilution13
2
3,091
210
61,073
64,205
69,556
313,000
c
a Test Conditions:
Total Volume Discharged = 5000 bbl
Initial Dye Concentration = 250,400 ppb
Background Suspended Solids = 0.1-2.4 mg/1
Bulk Density = 1.19 g/cm3
b Dilutions are calculated using a modified solids concentration obtained
by subtracting the ambient suspended solids concentration (assume an average
of 1.0 mg/1) from the measured concentration.
c Background levels reached.
C-19
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TABLE C-13.
SUMMARY OF MINIMUM DILUTIONS FOR DRILLING MUD
DISCHARGES TO TANNER BANK*
Discharge
Rate Distance
(bbl/h) (m)
10 0
105
155
450
10 0
76
145
440
12 80
160
225
290
450
12 0
90
130
175
250
20 0
55'
140
200
275
754 0
74
500
625
800
1,000
Depth Current
(m) (cm/sec)
12 11.8
12
8
23
12 45.2
15
15
5
15 14.9
5
15
10
10
12 29.8
10
15
15
20
10
12 2.2
10
5
10
15
5
12 15.9
10
5
20
20
25
Transmittance
(Percent)
>
49.1
62.8
77.1
66.6
65.7
48.4
57.6
74.7
75.7
74.0
84.8
_
46.4
51.6
74.6
77.5
83.3
28.4
41.3
40.5
63.4
55.6
_
0.0
19.3
80.8
23.7
10.9
Suspended
Solids
(mg/1)
499
5.2
2.03
1.79
252
1.95
1.17
1.01
1.06
0.978
0.614
1.44
0.724
43.04
1.59
2.20
2.11
1.33
1.51
279.2
2.74
1.81
2.18
1.01
1.56
328
25.2
4.04
1.10
4.73
0.563
Mi nimum
Dilutionb
502
59,524
242,718
316,456
996
263,158
c
c
c
c
c
c
c
5,947
423,729
208,333
225,225
c
c
899
143,678
308,642
211,864
c
c
765
10,331
82,237
c
67,024
c
a Test Conditions:
Initial Solids Concentration = 250,000 mg/1
Background Solid Concentration = 0.81-1.5 mg/1.
b Dilutions are calculated using a modified suspended solids concentration obtained
by subtracting the background concentration (1.0 mg/1) from the measured concentration.
c Background levels reached.
C-20
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APPENDIX D
FIELD OBSERVATIONS OF SOLIDS DEPOSITION
-------
FIELD OBSERVATIONS OF SOLIDS DEPOSITION
Northern Technical Services (1981, pp. 87-91) conducted a study (Table
C-l) to measure bottom deposition in the Beaufort Sea (Reindeer Island).
Settling pans were deployed at various locations in the vicinity of the
discharge. In the deep water test [8.4 m (28 ft)], larger particles were
deposited near the discharge while finer materials and drilling mud were
deposited further away. The maximum deposition of drilling muds was 173
mg/cm^ at 6 m (20 ft) from the discharge. Little deposition of drilling
muds and cuttings occurred at distances greater than 30 m (98 ft) from
the discharge. Drilling muds were quickly resuspended and carried away
after initial deposition (Northern Technical Services 1981, pp. 87-88).
Northern Technical Services (1983, pp. 40-51) also conducted deposition
studies at Tern Island [6.7 m .(22 ft)J in the Beaufort Sea. Predischarge
and postdi scharge sediment samples were collected to determine if drilling
effluents (mud discharges only) accumulated on the seafloor. Grain size
and trace metal sediment analyses showed no indication of drilling effluent
accumulation.
Ecomar (1983, pp. 25-26. 49-60, 75-77) deployed 22 sediment traps
[1 m (3.3 ft) above the seafloor] at various distances up to 967 m (31,725 ft)
downcurrent from the drilling platfonm in 12 to 13 m (39 to 43 ft) of water
in Norton Sound (COST well no. 2). The majority of solids settling occurred
within 100 to 125 m (328 to 410 ft) of the discharge. Highest accumulations
occurred in the sediment traps placed within 50 m (164 ft) of the discharge.
Solids accumulations ranged from 2 to 1,740 g/m2. The maximum deposition
(1,740 g/m2) occurred at 12 m (39 ft) from the source (Ecomar 1983, p. 49).
Nearfield sedimentation could not be completely described by the selected
placement of the sediment traps near the source. At distances greater
than 300 m (984 ft) from the discharge, solids accumulations in the traps
D-l
-------
were near the measured background level (Ecomar 1983, p. 55). Trace metal
analysis of sediment samples did not show significant accumulation of barite
or chromium. "However, background sedimentation rates (3 g/m2/h due to
a storm) were relatively high during the test, so the results may reflect
the contribution of background sedimentation rather than accumulation of
drilling materials.
Sedimentation studies were performed by Ecomar (1978, pp. 238-291)
at Tanner Bank to trace the settling and bottom transport of drilling dis-
charges. Nineteen sediment traps were deployed 10 m (33 ft) above the
bottom at various distances from the platform. Grab samples of bottom
surface sediments were collected prior to, during, and after drilling opera-
tions. Cuttings and drilling mud solids were deposited in sediment traps
up to 125 m from the source, but were not detectable at 915 m (3,002 ft).
Maximum induced sedimentation (67 g/m^/day estimated) occurred approximately
64m (210 ft) downcurrent. Measurable induced sedimentation was absent
at the control trap [915 m (3,002 ft) downcurrent]. Detectable but insigni-
ficant accumulations of discharged materials were present at some downcurrent
stations within 125 m (410 ft) of the source.
Deposition studies (bottom sampling, television monitoring, and sediment
traps) in 62 m (203 ft) of water in Lower Cook Inlet showed little accumulation
of cuttings on the bottom (Houghton et al . 1980, p. 285). The cuttings
deposition rate varied from 5.24 x 103 g/m2/h [at 85 m (279 ft)] to 1.25
g/m2/h within 100 m (328 ft) of the discharge. No cuttings were identified
in the control trap located 2.9 km (9,514 ft) from the source.
Deposition studies of drilling fluids were conducted by Gettleson
(1978) in East Flower Garden Bank, Gulf of Mexico. Test conditions included
129 m (423 ft) of water and bottom currents toward the west-southwest.
Results showed that drilling fluids and cuttings were distributed to 1,000
m (3,281 ft) from the discharge.
An offshore drilling site approximately 50 km northwest of Palawan
Island, Philippines was examined 15 months after well completion to determine
impact of drilling operations on coral growth (Hudson et al., 1982, pp. 890-
D-2
-------
908^
>' Drilling took place in 26 m (85 ft) on the reef with 3 cm/sec (0.10
c' currents to the north. Data was gathered using divers, coral cores,
otomosaics. No trace of a cuttings pile was found, but some cuttings
were orphan*
m sediment-filled depressions within 20 m (66 ft) of the
(Hudson et al . 1982, p. 907).
of dnliing discharges (cuttings and drilling muds) in the mid-
t antic (off the New Jersey coast) was studied by EG&G Environmental Consul -
P. 3-1 through 5-2) using side-scan sonar mosaics, sediment
samples, underwater television monitoring, and bottom photographs. Drilling
took place in 120 m (394 ft) of water with bottom currents typically less
than 10 on/sec (0.33 ft/sec). Physical effects of the discharge were observed
1 year after drilling. Visual observations indicated that within 100 m
(328 ft) of the discharge, accumulations consisted of numerous small piles
of drilling materials (mostly cuttings). Elevated barium levels in sediments
occurred out to 1.6 km (5,249 ft) from the discharge (EG&G Environmental
Consultants 1982, pp. 4-7, 4-9). Results of these studies showed that
physical alterations of the sediments near the well sites are long-lasting
due to the low energy nature of the mid-Atlantic site.
Deposition studies on Georges Bank 2 years after drilling had ceased
(Bothner et al., 1983, pp. 12-30) showed similar results. Studies were
conducted in 80 m (262 ft) and 140 m (459 ft) of water with residual bottom
currents of 3.5 cm/sec (0.11 ft/sec). Results of sediment core analyses
showed evidence of cuttings accumulation within 500 m (1,640 ft) of the
source (Block 410) (Bothner et al . 1983, p. 13). Elevated barium levels
(two times the background level) in sediments occurred at stations approximately
2 km (6,562 ft) from the source.
Crippen et al . (1980. pp. 636-669) conducted studies in the Canadian
Beaufort Sea to determine the concentrations of metals in sediments and
benthic fauna following drilling. Drilling took place from an artificial
island that was in an advanced state of erosion at the time of the survey.
Elevated levels of mercury, lead, zinc, cadmium, arsenic, and chromium
were found in sediment samples collected within 45 m (148 ft) with elevated
mercury levels out to 1,800 m (5 gos ft\ M
" ^>yui> ft). Mercury contamination of sediments
D-3
-------
was obvious within 100 m (328 ft) of the discharge (Crippen et al. 1980,
p. 641). However, coarse grained material from the island was observed
out to a distance of 300 m (984 ft) (Crippen et al. 1980, pp. 640, 645).
Tillery and Thomas (1980, pp. 562-581) conducted studies in the Gulf
of Mexico to determine the distribution of metals in sediments. Twenty
study sites (platforms) were located in less than 18 m (59 ft) to 92 m
(302 ft) of water. Sediment samples were collected at distances of 100 m
(328 ft), 500 m (1,640 ft), 1,000 m (3,281 ft), and 2,000 m (6,562 ft).
These data show decreasing surficial sediment concentrations with distance
from the source for barium, cadmium, chromium, copper, lead, and zinc (Tillery
and Thomas 1980, p. 565). However, concentrations of cadmium, chromium,
and copper measured at primary stations were similar to those measured
at control stations.
D-4
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