SURVEY OF METHODS TO DETERMINE
TOTAL DISSOLVED SOLIDS CONCENTRATIONS
U.S. ENVIRONMENTAL PROTECTION AGENCY
UNDERGROUND INJECTION CONTROL PROGRAM
WASHINGTON, D.C.
EPA LOE CONTRACT NO. 68-03-3416
WORK ASSIGNMENT NO. 1-0-13
KEDA PROJECT NO. 30-956
SEPTEMBER 1988
PREPARED BY
KEN E. DAVIS ASSOCIATES
UNDER SUBCONTRACT TO
ENGINEERING ENTERPRISES, INC.
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TABLE OF CONTENTS
SECTION PAGE
1.0 INTRODUCTION 1-1
1.1 Purpose and Organization of Report 1- 1
1.2 Background Information 1- 2
2.0 CONCLUSIONS 2- 1
PRINCIPLES
3.0 LOGGING METHODS AND PRINCIPALS 3- 1
3.1 Determination of Rw 3- 1
3.2 Resistivity - Porosity Method 3- 2
3.2.1 Resistivity Tools 3- 3
3.2.2 Porosity Tools 3- 5
3.3 Spontaneous Potential Method 3- 6
3.4 Rw VS TDS Concentration 3- 8
4.0 PROCEDURES FOR TDS DETERMINATION 4- 1
4.1 TDS Using Resistivity - Porosity (RP) Logs. 4- 1
4.2 TDS From Spontaneous Potential (SP) Logs... 4- 7
4.3 Precision and Accuracy of RP and SP
Msfctiocls.. - - -- = - = = = 4 — ± 2
4.3.1 The Resistivity-Porosity (RP)
Method 4-12
4.3.2 The Spontaneous Potential (SP)
Method 4-14
4.3.3 Precision and Accuracy Summary 4-17
4.4 TDS From Water Analysis 4-18
4.5 Comparison of Methods Used to Determine
TDS Concentrations 4-19
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Table of Contents
Page Two
SECTION
PAGE
5.0
COMPARISON OF RESISTIVITY - POROSITY VS
SPONTANEOUS POTENTIAL METHOD
5- 1
6.0
OTHER METHODS
6- 1
7.0
REFERENCES
7- 1
TABLES
1 COMPARISON OF RP METHOD AND SP METHOD FOR
NO.
1 SALINITY - RESISTIVITY CHART
2 NaCl - RESISTIVITY VS TDS CONCENTRATIONS
3 FORMATION FACTOR VS POROSITY
4 SP CORRECTION FACTOR VS BED THICKNESS CHART
5 EMPIRICAL SP CORRECTION CHART
6 MUD WEIGHT CORRECTIONS
7 ESTIMATION OF FORMATION TEMPERATURE
8 Rw VS Rweq AND FORMATION TEMPERATURE
9 Rweq DETERMINATION FROM THE SSP
10 RESISTIVITY SYMBOLS USED IN LOG INTERPRETATION
TDS DETERMINATION
2-3
FIGURES
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Table of Contents
Page Three
APPENDICES
APPENDIX 1 EXAMPLE 1-CALCULATION OF TDS USING RP AND SP METHODS
APPENDIX 2 WATER ANALYSIS AND LOGS FOR SECTION 4.0
APPENDIX 3 SINCLAIR VARIABLE MULTIPLIERS
APPENDIX 4 HINGLE CROSS PLOT
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ACKNOWLEDGEMENTS
This report was prepared at the request of the Environmental
Protection Agency, UIC Branch, Washington, DC. by Ken E. Davis
Associates under subcontract to Engineering Enterprises Inc. and
was funded through UIC Contract No. 68-03-3416, Work Assignment
No. 700-013-01. The following individuals were involved in the
preparation and review of this report:
Ken E. Davis Associates
Principal Author: Mr. Richard Lyle
Office Manager: Mr. Kim Forster
Engineering Enterprises, Inc.
Work Assignment Manager: Mr. J. L. Gray
UIC Program Director: Mr. Talib Syed
U. S. Environmental Protection Agency
Work Assignment Manager: Mr. Mario Salazar
Project Officer: Mr. Robert Smith
Technical Reviewer: Mr. Dan Chadwick
Technical Resource: Mr. Gene Coker (EPA Region IV)
Input and technical criticism by Mr. John Dewan, Dewan and
Timko, is appreciated; especially in the area of precision and
accuracy of TDS determination methods presented in this report.
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SYMBOLS USED
a - Pore Geometry
F - Formation Factor
K - Constant Related to Temperature
m - Matrix Cementation
R - resistivity
Rm - Mud Resistivity
Rmc - Mud Cake Resistivity
Rmf - Mud Filtrate Resistivity
Rmfeq - Equivalent Resistivity of Mud Filtrate
Ro - Resistivity of Formation
100% Percent Saturated with
Water of Resistivity Rw
Rs - Resistivity of Surrounding Formation
Rt - True Formation Resistivity
Rw - Formation Water Resistivity
Rweq - Equivalent Resistivity of the
Formation Water
SP - Spontaneous Potential Reading
SSP - Static Spontaneous Potential Reading
TDS - Total Dissolved Solids Concentrations
T - Temperature
Tf - Formation Temperature
6
- Porosity
Dimensionless
Dimensionless
Fahrenheit
Dimensionless
Ohm-meters
Ohm-meters
Ohm-meters
Ohm-meters
Ohm-meters
Ohm-meters
Ohm-meters
Ohm-meters
Ohm-meters
Ohm-meters
Millivolts
Millivolts
ppm
Fahrenheit
Fahrenheit
Decimal
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1.0 INTRODUCTION
1.1 PURPOSE AND ORGANIZATION OF REPORT
The intent of the U.S. Environmental Protection Agency's
Underground Injection Control (UIC) regulations is the protection
of underground sources of drinking water (USDWs) from improper
injection operations. In order to protect USDWs, a necessary
prerequisite is to identify USDWs and determine the depth to the
base of the lowermost USDW in the vicinity of injection wells.
The purpose of this document is to survey the techniques
used to identify USDWs via TDS concentration determination. A
comparison of the most commonly used methods of estimating TDS
concentrations from electric logs is presented with discussion of
laboratory methods. The approaches utilized are simple,
practical methods for determining TDS concentrations from open
hole geophysical logs. In most field applications all of the
data necessary to apply these techniques is available. The
methods described will yield good (+ 15%) approximations of TDS
values in most cases when compared to chemical analyses. More
elaborate techniques for special applications are referenced but
not addressed in detail.
Section 3.0 of this document presents an analysis of the
theory and tools involved in water salinity determinations using
electric logs. Detailed procedures and a step-by-step checklist
for two methods of electric log TDS determination are given in
Section 4.0. Reference figures needed for calculating TDS values
are included in a separate section at the back of the report. In
1-1
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Section 4.0, illustrative examples utilizing the electric log
procedures are explained and compared to other procedures to
develop conclusions regarding the precision and accuracy of
electric log methods.
A comparison of the two methods presented, reference to
other methods of TDS determination, conclusions, and references
are presented in Sections 5.0, 6.0, and 7.0 respectively.
This report is not intended to introduce the reader to
geophysical logging techniques. A prior understanding of well
construction, logging, and log interpretation is therefore
recommended.
1.2 BACKGROUND INFORMATION
The objective of the Environmental Protection Agency (EPA)
Underground Injection Control (UIC) Program is to protect
underground sources of drinking water (USDWs), those aquifers
that contain less than 10,000 parts per million (ppm) Total
Dissolved Solids (TDS). UIC regulations were created to protect
potentially usable aquifers from contamination related to the
underground injection of fluids. Although aquifers with greater
than 500 ppm TDS are rarely utilized for drinking water supply,
it is believed that imposing protection for waters with less than
10,000 ppm TDS will ensure adequate supply (through treatment)
for future generations.
1 - 2
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EPA UIC regulations addresses five different well types:
Class I wells, those that inject hazardous or
non- hazardous industrial and municipal waste
below any USDW;
Class II wells, those that inject fluids
related to the production of oil and gas;
Class III wells . which inject fluids for
extraction of minerals;
Class IV wells, which inject hazardous wastes
directly into a USDW (currently banned); and
Class V wells, those not included in Classes
I, II, III, and IV.
Although this report uses examples from Class I and II injection
wells, the methodologies of determination of TDS concentration
are applicable to the regulation of all well classes.
Three general criteria for Class I and II injection wells
are:
1. Injection must take place below the lowermost
USDW (unless exempted).
2. USDWs penetrated by the well must be
protected (preferably by cemented longstring
casing) .
1 - 3
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3. There should be a sufficient confinement zone
separating the injection strata from the
lowermost USDW.
Obtaining useful information regarding ground water quality-
is essential for a determination of whether the above criteria
are met. For newly drilled wells, this information can often be
documented directly through a comprehensive sampling program.
For older wells or new wells where sampling was not performed,
indirect methods must be employed to determine ground water
quality. Electric log methods described in this report provide a
means by which ground water quality information can be obtained
indirectly from existing geophysical log data.
Historically, operators of Class I and II wells have
run the necessary geophysical logs for ground water quality
determinations. The current regulations promulgated under 40 CFR
144, 146 and 148 require an increasingly comprehensive suite of
geophysical logs. These logs should provide a good basis for
determining TDS concentrations which will, in turn, improve
identification of USDWs.
1 - 4
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2.0 CONCLPSIONS
The goal of current UIC regulatory programs is the
protection of potential drinking water aquifers from injection
operations. This goal can be accomplished by defining
appropriate well construction in relation to the base of USDWs to
ensure proper confinement of the injected fluids. This report
describes two methods, Spontaneous Potential (SP) and
Resistivity-Porosity (RP), which may be used to identify USDWs
using geophysical logs. Both methods provide reasonable TDS
estimates (+ 15%) in relation to chemical analyses if sufficient,
accurate data is available. Sampling and chemical analyses is
the benchmark method to determine TDS concentrations.
However, in many cases chemical analyses may not be
available, simply because the formations were not sampled when
the wells were originally drilled and completed. In such
instances, geophysical logs serve a useful purpose in estimateing
TDS concentrations.
The relationship between TDS and formation fluid resistivity
should be established for USDWs in the vicinity of all injection
sites where water quality is uncertain. TDS values can be
contoured and recorded for future reference, providing a library
of USDW locations.
The SP method is the preferred measurement technique when:
1) Fresh borehole fluids (Rmf > Rw) were used
during logging,
2 - I
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2) Deep reading Electric logs are not available
3) Formation and borehole resistivities are
significantly different resulting in large SP
deflections, and
4) Thick sand/shale beds are present.
The RP method should be used when:
15 Low porosity, thin bed carbonate formations
are of interest,
2) Accurate formation porosi ty is available, and
3) Salt based muds occupied the borehole during
logging.
Table 1 presents a summary of the applicability and
limitations of each method.
For quality control purposes, when data is available, both
methods should be used to calculate TDS concentration. If
inconsistencies are noted, a careful review of input data is
necessary. Additional quality control measures can be
incorporated by calculating TDS values at mult iple well sites
within a given area. If multiple well sites are used with
similar hydrogeologic properties, the errors associated with the
measure of TDS concentrations should become obvious and
consistent TDS concentrations from log evaluation can be
estab I ished.
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TNBLE 1: COHPMtlSCW OF HP M3CBCD AND SP M5CHCD FCR "EDS HEQSWNKnON
igracp
DM* NSSDS AM)
Accurate formation
percsity
Fomat-cn temperature
~c:-ot .-:r, factor if)
ECC-r
- of fore-
st: or. Fc; -e&scrpd
with jeep reading'
electric log
- Formation water resis-
tivity tV! calculated
tzar. Ro
- 756 legated fran Rw
ADVANTAGES m)
Vantages=
-Can be used in most
cases if needed data
is available
- When deep reading
electric log is
available
- When porosity data is
available
- When highly saline
borehole fluids were
present during logging
- When Rw > 1 ohm-m
- Lou porosity, thick bed,
carbonate foraations.
- when formation and
borehole resistivities
are similar
- When thin beds are
present
DISfiDV»M»ffiS AND
Disadvantages:
- Requires measurement of
porosity (additional
data)
When logging tool electrode
spacing is greater than bed
thickness
When oil base muds were
present during logging
(resistivity logs should
not exist)
Major ion distribution
Formation porosity
Formation type and
degree of sedimentation
(affects P!
Formation temperature
«XORflCY
- Absolute +15%
- Measurement of
differences in sane
formation +7%
- Errors of up to 30%
can exist at low TDS
values (_10,000 ppn)
if major ion equi-
valents are not cal-
culated. NaCl tends
to become less
dominant when TDS
<10,000 ppn
(shallower depths)
Approximate distri-
bution of ions present
Poraation ten^erature
eorenole fluid resis-
tivity during logging
;j>r;
Correction dsarts
Spontaneous Potential
:SP' between foraa-
ticr. arc borehole
9qt;:valent formation
«aee: resistivitv
calculated fras
Pwnc, 3nf, S? relation-
ship
• Sxeq used to calculate
Rw
TT6 calculated fran 2w
¦ Quick and easy
(esquires only one log)
¦ Many old electric logs
can be used
When porosity data is
unavailable
When fresher (low-
salinity! borehole
fluids were present
during logging
When Rw < 1 ohre-m
¦ irtxin fttt >> Rw
Disadvantages;
- Must assume major ion
concentration is NaCl
- Requires accurate Rm
measurement
- Correction factors must
be applied for shale
presence, bole diameter,
mud invasion, and bed
thickness
wten Mo<; to Use;
- When formation and bore-
hole resistivites are
similar
- When thin beds are
are present
- When thick, low porosity
carbonates are of interest
- When highly saline borehole
fluids were present during
logging
- When fornation and borehole
fluid resistivites are
similar
- When oil base muds were
present during logging (SP
log should not exist)
- Major ion distribution
- Borehole fluid resis-
tivity
- Fornation temperature
- Shaliness of formation
- Hole diameter
- Mud invasion from
borehole
- Bed thickness
- Absolute +14%
- Measurement of
differences in same
formation +7%
- Errors of up to 30%
can exist at low TDS
values (210,000 ppn)
if major ion equi-
valents are not
calculated. NaCl
tends to become less
dominant when TBS
110,000 ppm
(shallower depths)
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If both logging methods are used to calculate TDS
concentrations for a single well with no water analysis
available, and both estimates are close, a conservative approach
would be to choose the lower TDS concentration. If the
difference becomes large, differing by a factor greater than 2,
and a review of the input data reveals no obvious errors,
accurate TDS concentrations can not be determined from
geophysical logs.
Certain errors are inherent with geophysical logging
techniques and can not be avoided. Existing data is usually
developed from multiple sources and determining the origin of
errors is difficult.
Errors associated with the accuracy and precision of TDS
concentrations measured with chemical analysis include:
1) The original input data
2) Laboratory error
3) Non representative samples
TDS concentration developed from chemical analyses is the
preferred method of determining formation water quality.
Electric log methods can be used when chemical analyses are not
ava ilable.
2-4
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3.0 LOGGING METHODS AMD PRINCIPLES
3.1 DETERMINATION OF Rw
Geophysical logging of the earth's subsurface provides a
fundamental means of determining the properties of rock matrix,
formation fluids, and the soundness of veil construction.
Through the interpretation of these logs, a variety of
characteristics can be determined, including well-bore
conditions, lithology, porosity, reservoir/aquifer conditions,
and formation/fluid resistivity. Geophysical logs can provide
base line records which, when compared to logs run in later
years, indicate changes throughout the history and operation of
the well. Through a comparison of logs and drilling data
compiled at a single well point with logs from neighboring wells,
the nature of subsurface strata can be determined for a given
area. Geophysical logs and related geological data can be
acquired from geologic surveys, petroleum information companies,
log libraries, and other sources.
In this report we discuss the determination of TDS content
utilizing log derived values for connate water resistivity (Rw).
TDS concentrations can be estimated from Rw values, since
resistivity is proportional to TDS content. The electrical
resistivity of the rock (Rt) is dependent upon the rock matrix
and the fluid contained within the pore spaces. Typically, the
water contained within the rock is more conductive than the rock
itself. In other words, it is less resistive. The resistivity
of the formation that is completely saturated with 100% water of
3 - 1
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resistivity Rw, is referred to as Ro. Resistivity terminology is
shown graphically in Figure 10.
Formation water resistivity is a function of salinity and
temperature as seen in Figure 2 (Alger 1966) . The higher the
temperature, the lower the resistivity for a specific salinity.
At room temperature, the resistivity of potable water is about 10
ohm-meters, sea water about 0.2 ohm-meters, and a saturated
saltwater solution 0.04 ohm-meters (Hilchie 1978).
A variety of work related to determination of water
resistivity via indirect techniques has been published by the
petroleum industry because of Rw's application to the location of
oil and gas reserves. Two methods have been developed from oil
and gas technology to indirectly determine Rw. One method, the
resistivity-porosity (RP) method, relies on a response from a
deep reading electrical log combined with the corresponding
formation porosity. The second method, the spontaneous potential
(SP) method, uses differences in the naturally occurring direct
current potential and known borehole fluid characteristics. The
two geophysical methods usually will not give specific ion
concentrations, but do characterize ground water, and can be used
to estimate Total Dissolved Solids (MacCary 1980) .
3.2 RESISTIVITY - POSOSITY METHOD
The resistivity-porosity method requires knowledge of the
formation resistivity and formation porosity. Formation
resistivity may be determined from a deep reading electric log.
The purpose of any deep reading electric log is to measure true
3-2
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formation resistivity (Rt) independent of borehole fluid and
invasion. Invasion refers to the contamination in the near
wellbore area of the formation fluids by drilling fluids.
Electric logs have different depths of investigation depending
upon electrode spacing and type of focusing. In high porosity
zones where beds are thick, the RP method can be used if the
electrode spacing is less than the bed thickness.
Rw values from the RP method are derived from a combination
of logs, using porosity and saturated formation resistivity (Ro)
values. The RP methodology is presented in Section 4.0.
3.2.1 Resistivity Tools
Three types of resistivity tools have been commonly used for
deep resistivity measurements. These include laterologs (focused
current logs), induction logs, and the basic electrical survey.
Laterologs are focused or guarded electrode systems (Dresser
Atlas 1982). Guard electrodes are placed above and below a
current electrode and kept at the same potential to focus the
formation current into a thin disc flowing perpendicularly to the
borehole. The radius of investigation is approximately equal to
the length of the guard electrode. The focused current log
defines bed boundaries very well and is not affected much by
adjacent bed resistivities. The short guard logs are used for
measuring the resistivity of the flushed or invaded zone near the
borehole. The longer guards are used for measuring the true
resistivity of the uncontaminated zone when the mud filtrate
3-3
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resistivity is not more than four times the formation water
resistivity. The laterolog can resolve beds as thin as 2 feet.
The laterolog works well in salt based muds. Salt based
muds are typically used when drilling in areas where salt
sections, such as halite, are common. These muds are used to
prevent washouts (borehole enlargement due to dissolving or
sloughing). The laterolog also works well in formations with
high resist ivity. These tools are much superior to ES
(Electrical Survey) devices for large Rt/Rm ratios (salt muds
and/or highly resistive formations) and for large resistivity
contrasts with adjacent beds (Rt/Rs or Rs/Rt) (Schlumberger
1987).
Induction logs apply an alternating current which induces an
eddy current in the formation. The resulting secondary magnetic
field induces a voltage in a receiver coil. This voltage is
directly proportional to formation conductivity which is
presented as a resistivity value on most logs. Focused induction
logs have proven to be the best method for obtaining formation
resistivity in wells drilled with fresh mud, air, or oil based
mud; and with beds at least six (6) feet thick (Dresser Atlas
1982). Induction logs work best when the formation resistivity
is lower than the borehole fluid resistivity. This is typical of
fresh mud systems.
Under favorable logging conditions, induction log values may
be used for true resistivity; however, charts are provided by
3-4
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logging service companies to make corrections for thin beds,
large diameter boreholes, etc.
Many older wells have only one log available for
interpretation. These logs were difficult and, sometimes
impossible, to interpret (Dewan, 1983). These logs, called
Electric logs (today electric logs are a general term for all
geophysical logs) or Electrical Survey tools, were the basic and
most frequently used log until the middle 1950's. Electric logs
are still useful in determining resistivity of the virgin
formations provided the formations are relatively thick and the
deep curve is used. Extensive charts are required to correct for
borehole diameter, bed thickness, and adjacent-bed resistivity
effects (Hilchie 1979). For further information about old
Electric logs, Rollyn Frank (1986) has published an education
guide which is very useful.
3.2.2 Porosity Tools
As mentioned earlier the RP method requires both true
formation resistivity and formation porosity. Porosity may be
determined from geophysical logs if core data is not available.
Three types of logs available for porosity determination are the
neutron log, density log, and acoustic log. All porosity logs
are affected by rock matrix and borehole fluids. By isolating
these effects, accurate porosity determinations can be made. If
either the compensated neutron or the density log is used alone
to calculate porosity, then the lithology of the zone must be
3-5
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known in order that proper porosity calibration lines may be
constructed (MacCary 1980).
3.3 SPONTANEOUS POTENTIAL METHOD
When fresh drilling mud filtrates are in contact with more
saline formation water, a small electrical current is generated.
This current creates a voltage change, or potential difference in
the mud filled borehole opposite sand-shale interfaces.
Measurement of this voltage change by a geophysical logging tool
generates a Spontaneous Potential (SP) curve. The SP curve's
deflection is indicated on the log in millivolts. SP values of a
known shale section are usually constant and are depicted as the
shale baseline. These values are typically the furthest
deflections to the right of the SP curve. The SP curve shift is
a response to the formation fluid and drilling mud resistivity
differences. The SP method utilizes this response to determine
formation water resistivity. A formation containing salt water
must be at least slightly permeable, however, for SP character to
develop (Dresser Atlas 1982) .
Significant corrections may be required for accurate SP
measurement in many cases. If the formation is interbedded with
shale, a shaliness correction may be applied. If the bed is
thin, it should be corrected for thickness using charts or
standard correction factors. Effects due to hole enlargements
are generally small, and usually do not require
corrections. Correction factors are published by major open-hole
logging companies. One of the better sources is provided by
3-6
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Schlumberger. It should be noted that, regardless of the
magnitude of the bed resistivity, if the bed is thick enough, the
SP will reach static conditions (Hilchie 1978). The static
spontaneous potential (SSP) curve refers to a maximum deflection
between two fluids of different salinity and a shale section.
Although the SP method works well in sand-shale sequences,
it works poorly (if at all) in thick carbonate rocks of low
porosity (MacCary 1980). The method works satisfactorily at less
than 10,000 ppm TDS provided both mud filtrate and formation
water are of similar composition, and Rmf is much greater than Rw
(Vonhoff, 1966).
The SP log has its best application where fresh water based
mud is used to drill a well. The SP curve cannot be recorded in
holes with nonconductive drilling fluids, such as air or oil base
muds. The SP method should not be used when resistivities of the
borehole fluids and formation waters are similar unless
additional logs are available to pick clean formations since the
deflection of the SP curve will be extremely small. In typical
salt water base muds, the SP is often useless because the SP
magnitudes at depths of interest are small (Rmf = Rw) and because
boundary definition with low resistivity mud and high resistivity
formations is extremely poor (Dewan 1983) . The log is still
useful in salt water base mud provided the salinity of the mud is
not too great.
The SP tool is an excellent choice for delineating permeable
beds from shale beds, provided the resistivities of the borehole
3-7
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fluid and formation water are not the same. The amplitude of the
SP curve is not a function of porosity or permeability. However,
the formation must be permeable in order for the SP deflection to
occur.
3.4 Rw VS TDS CONCENTRATION
The preceding discussion has identified two methods by which
formation water resistivity, Rw, may be determined. In the next
section procedures are given to apply each of these methods to
the estimation of TDS concentration in a zone of interest. It is
important to realize, however, that water resistivity is not a
direct indicator of the composition of dissolved solids. A
strong correlation usually exists between water resistivity and
the mass of ions present regardless of the dominant salt present
(i.e. calcium chloride, sodium chloride etc.) (Kwader 1985).
Typical water analyses for the majority of wells indicate that
the dominant anion is the chloride ion (Cl~) and the dominant
cation is Sodium (Na+) when TDS values are high (>10,000 ppm) .
In this report, it is assumed that the formation waters in
question are 100% saturated with NaCl solution. Sodium and
chloride ions typically become less dominant in shallower
formation waters with TDS concentrations of less than 10,000 ppm.
If the suspected formation waters contain ions other than Na+ and
CI", and if the chemical nature of the fluid is known, equivalent
sodium chloride concentrations can be determined. If the
concentration of each ion is known, the equivalent sodium
chloride concentrations are determined by multiplying each ion
3-8
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concentration by a "multiplier factor". A summation of the
multiplied ions yields an equivalent sodium chloride
concentration. The multiplying factors are more accurate at
concentrations less than 100,000 ppm. If equivalent sodium
chloride concentrations are not determined, TDS values derived by
the methods presented in this report can be in error by as much
as 30% (in fresh water sands with TDS < 10,000 ppm).
A detailed method of determining sodium chloride equivalent
solutions is included in Appendix 3. The method described is the
Sinclair variable multiplier technique (Desai and Moore, 1969)
which considers total ionic concentration of the water and
converts all ionic constituents of the water into an equivalent
NaCl concentration (MacCary, 1980 5. Other multiplying factors
have been developed (Lynch 1962) which are also appropriate.
3-9
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4.0 PROCEDURES FOR TPS DETERMINATION
4.1 TDS USING RESISTIVITY - POROSITY CRP) LOGS
The TDS concentration of an aquifer can be determined from
appropriate combinations of porosity and resistivity logs. If
adequate geophysical data is available, determining TDS
concentration is possible with the following information: 1) true
resistivi ty of the formation, 2) corresponding porosity, and 3)
the application of appropriate equations.
Archie (1942) expressed an empirical relationship between
formation resistivity [usually denoted as the formation
resistivity factor (F) ] , porosity, matrix cementation (m) , and
pore geometry (a) using the following equations:
F = RQ
Rw (1)
Equation (1) may be rearranged as follows:
Rw = Ro/F (2)
and
F = a(Archie equation) (3)
where
F = Formation resistivity factor (dimensionless)
a = Pore geometry coefficient (dimensionless)
<6 = Porosity (decimal)
m = Cementation factor (dimensionless)
Ro = Resistivity of 100% water-saturated formation
(ohm-meters)
Rw = Resistivity of formation water (ohm-meters)
4-1
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The Ro and 6 values can be determined using standard
methods. If several values of Ro vs <6 can be plotted on a log-
log graph, then "m" can be empirically determined (by the slope
of the resulting straight line) for any aquifer. The value of
"m" varies with the type of rock encountered, however.
Alternately, the table below can be used for typical ranges of
magnitude.
Values of Cementation Factor "m" (after Guvod, 1944)
Rock Type "m"
Highly cemented:
limestone, dolomite, quartzite 2.0 - 2.2
Moderately cemented:
consolidated sands 1.8 - 2.0
Poorly cemented:
friable, crumbly sands 1.4 - 1.7
Unconsolidated sands 1.3
The constant "a" is related to pore geometry and has been
developed through laboratory analysis. In the general case, a =
1. As illustrated in the subsequent discussion, the Humble
equation assumes a = 0.62 and m = 2.15, while the Tixier equation
uses a = 0.81 and m = 2.0.
Combining equations 2 and 3, and assuming a = 1 we have:
Rw = Ro (4)
4-2
-------
Equation (2) is an empirical relationship which holds well
for waters having resistivities less than one ohm-meter. It
tends to break down when Rw > 1 ohm-m, where surface conductance
of sand grains becomes significant (Alger, 1966). Equation (4)
shows that the product of the formation resistivity and the
formation porosity raised to the power m is equal to a number
that has a direct relationship with the formation water
resistivity, Rw.
Estimated TDS determinations can be made using Figures 1 and
2 if porosity (eS) and 100% saturated formation resistivity (Ro)
values can be obtained from a geophysical log, as discussed in
Section 3.2.
For generalized use of the Archie equation, we can use one
of the following empirical relationships. A more widely used
relationship for sands and sandstone formations is the Humble
equation:
F = .062/e52*15 (5)
Another similar interpretation is reflected in the Tixier
formula:
F = 0.81/ri2 (6)
which also applies to granular systems, but is easier to
calculate (Hilchie, 1980).
4-3
-------
Once porosity is determined, equations 5 and 6 can be
applied, or, the general Archie equation with an appropriate m
value may be used to determine formation factors. Equations 3,
5, and 6 are illustrated in Figure 3 along with recommended F-<6
relationships for various formations. Next, Ro (Ro = Rt in clean
water saturated zones) is picked from the electrical log. It is
important to note that laterologs are designed to measure high
resistivity while induction logs can be significantly in error
when measuring high resistivity (Alger, 1988). Values of Ro and
F are then substituted into equation 2, and a value of Rw is
determined. Assuming only NaCl ions are present, TDS
concentration of the formation can be determined using Figures 1
or 2 once Rw is known. However, when Rweq is greater than about
one ohm-meter, other ions such as calcium (Ca) , magnesium (Mg),
bicarbonate (HCO3), and sulfate (SO4) will tend to be present and
affect water resistivity in a manner different than sodium
chloride (NaCl) (Alger, 1966). In such cases only an equivalent
NaCl concentration is obtained from Figures 1 or 2.
The following procedural steps outline and summarize the
Resistivity-Porosity method for determining TDS, These steps are
followed in the examples included in Appendix 1.
1. Correlate porosity and electric logs if possible.
2. Determine clean permeable beds using SP, Gamma Ray
(GR) , and Ri/Rt separation.
4-4
-------
3. Determine porosity (from charts) of permeable beds
using:
a. Known lithology and 1 porosity log,
b. Cross plotting 2 or 3 porosity logs,
c. Assumed lithology with 1 porosity log,
or
d. Core analysis.
4. Determine formation temperatures:
a. From direct measured data, or
b. Using Figure 7.
5. Determine formation factor (F) by:
a. Calculation using the Humble (equation
5) , Tixier (equation 6) , or Archie
equation (3), or
b. Using Figure 3.
6. Determine Ro
a. The deep reading resistivity curve for
clean water bearing zones Rt = Ro (water
saturated formation)
b. Deep induction or laterolog picking a
value for Ro directly from the log.
7. Determine Rw using equation (2)
8. Check calculated Rw against additional source if
possible (SP method, water analysis).
9. Determine TDS concentration using Figures 1 or 2.
Rw, and therefore TDS, can also be determined using the more
complex Hingle resistivity porosity cross-plot (RPCP) method.
4 5
-------
The RPCP method involves plotting Ro (from deep resistivity-
logs) versus formation bulk porosity (neutron, density or
acoustic velocity logs) (Kwader 1985). The RPCP method is
outlined in Appendix 4. Examples of the RP method are presented
in Appendix 1 and below.
CASE HISTORY - CLASS I DISPOSAL WELL
CALCASIEU PARISH, LOUISIANA
Well Log Heading
BHT 90°F Surface Temperature 80°F
TD 2250 ft
Rm 5.63 ohm - m @ 76°F
Rmf 5.5 ohm - m @ 75°F
Mud Weight 9.7 ppg
Using the RP method calculate TDS concentration at the
suspected USDW, interval between 1110 - 1160 ft.
1) Determine porosity using bulk density and known
lithology
6 = 40%
2) Determine formation temperature using Figure 7
Tf = 85°F
3) Determine formation factor using Humble equation or
Figure 2
F = 0.62/d2-15
= 0.62/(0.40)2*15
4) Pick Ro from Dual Induction Log
Ro = 3.1 ohm - m
4 - 6
-------
5) Determine Rw using equation (23
Rw = Ro
F
Rw = 3.1 ohm - m = 0.7 ohm - m
4.45
6) Determine TDS concentration using Figure 1 or 9
TDS = 7000 ppm
4.2 TDS From Spontaneous Potential (SP) Logs
A second method used to determine TDS utilizes the
Spontaneous Potential (SP) curve. Static SP (SSP) refers to the
maximum SP that can be obtained given a shale-aquifer boundary
and two waters of different salinity. It is essentially the SP
that would develop if no current flowed. In clean formations
(non-shaley), the static SP is related to the resistivities of
the connate water (Rw) and mud filtrate (Rmf) according to the
following equation:
SSP = -K log Rmfeg
Rweq
(7)
where
SSP
the deflection of the SP curve from a shale
baseline (millivolts) in a thick clean zone.
K
a constant, (61 + 0 . 13 3)T f for NaCl water
dependent on temperature.
Rmf eq
equivalent resistivity of mud filtrate (ohm-
meters ) .
4-7
-------
Rweq = equivalent resistivity of connate water (ohm-
meters) .
Tf = formation temperature (F).
Input parameters for the static SP method are usually
readily available from standard logs. The value of SSP is read
directly from the log as discussed in Section 3.3 and illustrated
in Appendix 2. If the SSP needs to be corrected for thickness,
use Figures 4 or 5. Formation temperature can be calculated
using Figure 7 if bottom hole temperature and geothermal gradient
are not known. Rm or Rmf values are usually listed on the log
heading. A knowledge of mud resistivity is essential for
electric log interpretation. This property is almost always
measured by the logging crew, either on a surface sample or in
the borehole, and appears on the log heading. Temperature
corrections may be made using conversions presented in Figure 1.
If the mud resistivity value Rm is used, it needs to be converted
to Rmf. This is easily completed by using Figure 6. Rmfeq is
then determined using the guidelines at the top of Figure 9.
In most formation waters, there is enough NaCl that the K
value for NaCl (71 at 77°F) can be used. However, when other
salts are predominant in very fresh waters SSP responses may be
drastically altered. First the K value may be affected. For
example, if both filtrate and formation water were pure sodium
bicarbonate solution (NaHCO-j), K would be 56 at 77°F. For
potassium chloride solutions (KC1), K is approximately 60 at
77°F, and for potassium bicarbonate solutions (KHCO3) , K is
4-8
-------
approximately 45 at 77°F. More importantly the Rmfeq/Rweq ratio
in Equation 7 must be replaced by the ratio of ion activities in
the formation water and mud filtrate. If extensive logging work
is anticipated in an area where unusual salts predominate in the
formation water, empirical relations should be developed for that
area (Alger, 1966). Unusual salts are those other than sodium
chloride.
Rweq can now be determined by substituting Rmfeq, SSP, and
Tf values into equation 7. The final step is a temperature
correction made by converting the equivalent Rweq, just
calculated, into actual Rw using Figure 8.
As stated earlier, the procedures presented above are
applicable to Rw determination of formation waters that are
predominantly NaCl waters. In fresh formation waters, salts
other than NaCl may become more important. In such cases, the
dashed lines in Figure 8 which approximate "average" fresh
formation waters should be utilized to convert Rweq to Rw.
The following steps outline and summarize the SP method for
determining TDS:
1. Establish the shale baseline on the SP.
2. Pick out thick, clean permeable zones.
4-9
-------
3. Do all the thick zones have about the same SP?
if yes — read SSP in any thick zone.
if no — read SSP in a thick zone near the zone
of interest.
4. Determine formation temperature, using Figure 7 if
necessary.
5. Convert Rm from log heading to Rm at formation
temperature using Figure 2.
6. Determine Rmf from Rm at formation temperature using
Figure 6. Alternatively, if Rmf is given on the log
heading, correct it directly to formation temperature
using Figure 2. Convert Rmf to Rmfeq using guidelines
of Figure 9.
7. Read SSP amplitude from shale baseline to maximum
constant deflection.
8. If the SSP does not show a flat top, determine bed
thickness from SP inflection points and make a bed
thickness correction using Figures 4 or 5.
9. Determine Rweq using SSP from step 8 (corrected if
necessary) and Rmfeq, using Figure 9.
10. Convert Rweq to Rw with Figure 8.
11. Check Rw from SP against another source if available.
12. Determine TDS concentrations using Figures 1 or 2.
4-10
-------
Examples of the SP method are presented in Appendix 1 and
below.
CASE HISTORY - CLASS I DISPOSAL WELL
CALCASIEU PARISH, LOUISIANA
Well Log Heading
BHT 90°F Surface Temperature 80°F
TD 2250 ft
Rm 5.63 ohm - m @ 76°F
Rmf 5.5 ohm - m @ 75°F
Mud Weight 9.7 ppg
Using the SP method calculate TDS concentration at the
suspected USDW, interval between 1110 - 1160 ft.
1) Determine formation temperature using Figure 6
Tf = 85°F
2) Determine Rmf at formation temperature using Figure 1
and Rmf value listed on log heading.
Note: It is best to use the measured Rmf value on
the log heading, if shown, rather than
calculate the Rmf value from Rm.
Rm = 4.9 ohm - m @ 85°F
3) Pick the value for SP at depth in question.
SP = -60 mv
4) Determine Rmfeq using equations in Figure 9
Rmfeq = 0.85 Rmf
= 0.85 (4.9 ohm - m)
= 4.16 ohm - m
4 - 11
-------
5) Determine Rweq using Figure 9
Rmfea = 6.2
Rweq
Rweq = 0.67 ohm - m
6) Determine Rw from Rweq using Figure 8
Rw = 0.67 ohm - m
7) Determine TDS concentration using Figure 1 or 2
TDS - 7,500 ppm
4.3 PRECISION AND ACCURACY OF SP AND RP METHODS*
4.3.1 The Resistivity-Porosity (RP) Method
This method is generally applicable, even when waters
contain appreciable Ca or Mg ions, but does require a porosity
measurement. The applicable equation is (for clean sands):
Rw = <6m Ro (4)
0.81
where d is porosity (fractional), m is the cementation exponent,
and Ro is the deep resistivity reading (ohm-m) corrected for
invasion.
In the salinity range of interest, 500-10,000 ppm, the
relation between salinity S (ppm NaCl) and water resistivity, Rw
is (to an accuracy of 5%):
S = 5,500/Rw (12)
* By Mr. John Dewan
4-12
-------
Differentiating and using Eq. (12) leads to the following
uncertainty equations:
SS = 5Ro for 6 and m constant (9)
S ~ Ro
5S = m 5gS for m and Ro constant (10)
S 6
5S = (log_ m (11)
~5
These equations allow estimation of the uncertainty of
salinity determination under different assumptions:
A) Absolute salinity determination with a single well:
If the USDW is thick enough (^7') and the deep
resistivity reading (usually deep induction) corrected
for invasion, then Ro should be accurate to a probable
error of 5%. Eq. (9) gives the corresponding probable
error in salinity also as 5%.
Assuming good porosity logs are available
(specifically the density-neutron combination) the
probable error in porosity is estimated to be 5%. Eq.
(10), with m = 1.6, gives the corresponding probable
error in salinity as 8%.
Values of m for USDWs can vary considerably. They
are typically in the range 1.4 to 1.8. Without an
independent measurement, one must assume an average
value of 1.6 with probable error of 0.1, Eq. (11), with
6 = .32, .leads to a probable error in salinity of 11%.
4-13
-------
Combining these results, assuming independence of
error sources, leads to an overall probable error of
(52 + 82 + ll2 52 or 15%, in absolute salinity
determinations from a single well log- Note that, with
an "old" porosity log, such as sonic or microlog, the
probable error in porosity could be considerably larger
than that indicated.
B) Salinity differences across a given USDW:
Assuming, as before, the USDW is consistent in
characteristics across a number of penetrating wells,
then the probable error in relative salinities could be
significantly less. In particular, if the grain size
distribution in the USDW is relatively constant, then m
should be constant and the corresponding uncertainty in
salinity due to m considerably less. Overall, an
estimate of the uncertainty in relative measurements is
7%.
4.3.2 The Spontaneous Potential (SP) Method
This method is appl i cable if there is a good contrast
between mud filtrate and formation water salinities and if sodium
ions dominate in the chlorides. The SP equation (7) can be
written
Rw = Rmf - exp (SSP/K) (7)
where Rw (onm-m) is the resistivity of the formation water, Rmf
is that of the mud filtrate, SSP is the SP deflection (mv) from
4-14
-------
the shale line, in a thick, shale-free, water-bearing zone, and K
is a temperature-dependent constant given by
K = (61 + .133Tf) (13)
where T is the temperature in °F.
Combining eqs. (7) and (12) and differentiating we obtain the
following uncertainty relations:
S£ = .
5 Rmf
for SSP
and
T constant
(14)
s
Rmf
8S =
5SSP
for Rmf
and
T constant
(15)
S
K
££ =
.056
T SSP
for
SSP and Rmf constant
(16)
s
These equations allow estimation of the uncertainty of salinity
determination under different assumptions:
A) Absolute salinity estimation with a single well:
Rmf is measured at the surface by the logging crew
and is converted to the temperature of interest. Due
to continual alteration of mud properties during
drilling, Rmf downhole may deviate 10% (probable error
estimate) from the surface value. Eq. (14) indicates
that corresponding probable error in salinity
determination will be 10%.
The SSP measurement from the log is subject to an
estimated 3 Mv probable error from such sources as
baseline drift, surface-generated noise, slight
shaliness, etc. Assuming an average USDW temperature
4-15
-------
of 100°F, Eq. (15) indicates the corresponding probable
error in salinity to be 9.4%. Note, however, that
appreciable amounts of Ca and Mg ions in the water can
cause much greater errors in salinity determination.
Uncertainty in knowledge of the USDW temperature,
obtained by linear interpolation between surface and
bottomhole temperatures, is estimated to be 5°
(probable error). Equation (16) gives the
corresponding probable error in salinity (for an
average SSP of 30 Mv and temperature of 100°F) as 0.8%.
Thus temperature uncertainty is relatively unimportant.
Combining the results, assuming the sources of
error are independent, leads to an overall probable
error estimate of (102 + 9.42 + O.S2)1^2 or 14%, for
absolute salinity measurement from a single well.
Salinity differences across a given USDW from adjacent
well logs:
It is not possible to monitor salt water injection
into a USDW by running SPs successively over months or
years in the same well because the well is always cased
shortly after drilling. The next alternative is to try
to spot salinity variation across a USDW from adjacent
well logs.
4-16
-------
Assuming the OSDW is consistent in depth and in
freedom from shaliness, and that much the same drilling
mud practice has been used across the field, then the
probable error in relative salinity measurements is
estimated to be about half the absolute value given
above, i.e. about 7%.
4.3.3 Precision and Accuracy Summary
Both methods of analysis lead to a probable error estimate
of about 15% for single well measurements and about 7% for well-
to-well relative measurements. Many factors can degrade these
estimates, however, such as thin beds, washouts, no porosity
logs, only old ES logs, shaliness, etc. The particular
formations considered and the logs available need to be analyzed
in any specific case.
The best method of observing salinity changes using
geophysical logs is to have a plastic-cased observation well that
can be repeatedly monitored. In this case 6 and m are invariant
so the only uncertainty is in resistivity measurement. With
carefully calibrated tools, salinity changes as low as 3% should
be observable.
4.3 TDS PROM WATER ANALYSIS
Determining TDS concentrations from laboratory analysis of
water samples is the most precise method available. Analysis of
41 samples of water and wastewater were made with a standard
deviation of differences of 6.0 mg/1, (Standard Methods for the
Examination of Water and Wastewater, 1983).
4 - 17
-------
The standard method for determining TDS in water samples is
an evaporation technique where a sample is dried at constant
temperature and the weight of the remaining solids represents the
total solids- A detailed description of the technique is listed
in "Standard Methods for the Examination of Water and
Wastewater", 1983. This procedure is also described in EFA's
Method #160.2, "Non Filterable Residue Method".
Formation fluid samples were obtained and analyzed for the
Louisiana Class I disposal well case history. The average
conductivity for the samples in the interval 1110 - 1160 ft were
13,500 micromhos/cm.
Using the empirical formula developed by Turcan (1966) for
major aquifers in Louisiana:
(K)°.93 = TDS in ppm
K = conductivity in micromhos/cm
TDS = (13,500) 0 -93
= 6938 ppm
The fluid samples were also analyzed directly for TDS
concentration in accordance with the 15th edition of Standard
Methods of the Examination of Water and Wastewater and Methods
for Chemical Analysis of Water and Waste, EPA 60014-79-020.
The laboratory analysis (see Appendix 2) indicated:
TDS = 7020 ppm
4 - 18
-------
4.5 COMPARISON OF METHODS USED TO DETERMINE TDS CONCENTRATIONS
Results obtained using the described methods are summarized
below. All of the methods used (SP, RP, Turcan, and Laboratory
Analysis) are within an acceptable range.
A) The calculated difference between the RP and SP method
is:
7500 -7000 = 0.066 or 6.6%
7500
B) The calculated difference between the RP method and
laboratory water analysis is:
7000 - 7020 = 0.0028 or 0.3%
7000
C) The calculated difference between the SP method and
laboratory water analysis is:
7500 - 7020 = 0.064 or 6.4%
7500
D) The difference between the SP and RP method is within
an acceptable range. A review of the data did not
reveal any obvious sources of error.
E) Since the RP method value is nearly identical to both
the laboratory analysis and Turcan method, we can
conclude that the TDS is approximately 7000 TDS.
4 - 19
-------
Method
TDS Concentration (ppm)
RP 7000
SP 7500
Turcan 6938
*Water Analysis 7020
*Water Analysis contained in Appendix 2.
4-20
-------
5.0 COMPARISON OF RESISTIVITY-POROSITY VS
SPONTANEOUS POTENTIAL METHODS
Two methods of determining Total Dissolved Solids (TDS)
concentrations using geophysical logs have been presented in this
report. Both methods appear to have applications in determining
TDS concentrations when care is taken in selecting the input
data. There exists a workable relationship between water quality
and the use of geophysical logs. If it can be safely assumed
that major ion concentrations are composed of NaCl, the quickest
and easiest method for TDS determination is the SP method.
Therefore, for most situations, it is the preferred method.
Results are equivalent to those obtained by the RP technique.
Unlike the RP method, the SP method does not rely on correct
porosity measurements. If accurate Rmf data is available, final
results should be valid using the SP curve. The SP method is
subject to error if precautions are not taken. Factors affecting
the SP include: the presence of shale, borehole diameter, mud
invasion, bed thickness, and resistivity. Many older Electric
logs can be used for the SP method.
The RP method is Gc^udl 1 y sccurst© but rsc^uirss 3,ddit ionsl
data. Open hole logs such as induction and laterologs are
required, as well as accurate porosity measurements. To obtain
the best results, two types of porosity logs; such as the
neutron, acoustic, or density logs; are required unless accurate
lithologic descr iptions are available. Factors affecting the RP
include: the presence of shale, uncertainty in porosity if no
5 - 1
-------
porosity log is available, and the affeet of surface conductance
in fine-grained high porosity formations.
Both the SP and RP methods have different but equally
acceptable applications in determining TDS concentrations. The
relative values of borehole fluid resistivity and formation water
resistivity, and the quality of additional available data, will
dictate which method should be used. If the USDW is in a low
porosity, thick bed carbonate sequence the RP method must be used
as the SP will not resolve the beds. The RP method will also
need to be used if the borehole fluid is saline.
If Rw is determined to be less than 1 ohm-m (with the
dissolved salt being NaCl) both the SP and RP method are valid,
provided that good data is available. However, when Rw is
greater than 1 ohm-m, salts other than NaCl are probably present
causing the Rw value from the SP method to be low. Consequently,
when Rw > 1 the RP method is likely to be more reliable.
5-2
-------
6.0 OTHER METHODS
Several alternative methods are available for determining
the base of a USDW. These methods are usually researched before
geophysical logging techniques are selected.
Hydrogeological atlases are available from various Geologic
Water Surveys and several have been published by universities in
cooperation with state and federal governments. These
publications contain TDS concentrations in select formations.
Piezometric maps, oil and gas maps, water well location maps and
many other useful maps and charts are available for many areas.
Often times Rw can be obtained from water catalogs which
usually list chemical analyses collected from different locations
within an aquifer. These catalogs are compiled by oil and gas
companies, and professional organizations. Typically, Rw values
in USDWs are not included in the listing since aquifers
associated with oil and gas formations are normally not of low
enough TDS to qualify as USDWs.
The U.S. Bureau of Mines publishes information on oil-field
brines. Specifically, the U.S. Bureau of Mines publication No.
6167 has chemical analyses listed for brines in select
Mississippi and Alabama formations.
6 - 1
-------
Several methods of determining TDS concentrations through
chemical analyses of water samples are available. Unfortunately
samples of formation waters have rarely been taken near the base
of DSDWs. Where samples have been taken, direct measurements of
Rw (i.e. conductivity) are often listed even if a complete
analysis for all constituents is not performed.
Currently, new methods for ground water quality
determination are being developed. Several papers related to the
determination of ground-water quality and occurrence were
presented at the "Surface and Borehole Geophysical Methods and
Ground Water Instrumentation Conference and Exposition", NWWA,
October 1986. Techniques presented were applicable only to new
and exploratory wells. Thus, these techniques do not relate
directly to the determination of USDWs characterized through use
of existing geophysical logs from older wells.
6-2
-------
7.0 REFERENCES
Alger, R.P. 1966, Interpretation of Electric Logs in Fresh Water
Wells in Unconsolidated Formations, American Petroleum
Institute API RP 4S
Alger, R.P. 1988, Improved Fresh Water Assessment in Sand
Aquifers Utilizing Geophysical Well Logs, Presented at
Conference on Southwestern Ground Water Issues, Albuquerque,
N.M., March 1988.
Archie, G. E. 1942, The Electrical Resistivity Log as an Aid in
Determining some Reservoir Characteristics: American Inst.
Mining Metal. Engineers Trans. V. 146
Frank, Rollyn, 1986 Prospecting with old E-Logs, Schlumberger
Educational Services, Houston, Texas
Desai, K.P. and Moore, E.J. 1969, Equivalent NaCl Determination
From Ionic Concentrations, Log Analyst v. 10, no. 3
Dewan, J.T. 1983, Essentials of Modern Open-Hole Log
Interpretation, Tulsa Oklahoma, Dennwell Publishing Co.
Dresser Atlas 1982, Well Logging and Interpretation Techniques,
Dresser Industries Inc.
Gatlin, C., Petroleum Engineering-Drilling and Well Completions,
Prentice - Hall, Inc., Englewood Cliffs, N.J., 1960
Guyod, H., Fundamental Data for the Interpretation of Electric
Logs, Oil Weekly, October 30, 1944
Hilchie, D.W. 1979, Old Electrical Log Interpretation, Douglas W.
Hilchie Inc., Golden Colorado
Hilchie, D.W. 1980, Applied Openhole Log Interpretation Douglas
W. Hilchie Inc., Golden Colorado
Hingle, A.T., 1959 The Use of Logs in Exploration Problems,
Transactions, Society of Exploration Geophysicists, Los
Angeles, California
Kwader, Thomas, 1985, The Use of Geophysical Logs for Determining
Formation Water, Formation Magazine v24, No. 1, Jan.-Feb. 86
Lynch, E.T. 1962, Formation Evaluation: New York Harper and Row
Publishers
MacCarv, L.M. 1980, Use of Geophysical Logs to Estimate Water-
Quality Trends in Carbonate Aquifers, U.S. Geological
Survey-Water Resources Division, WRI-80/007
7 - 1
-------
Schlumberger Limited, 1979, Log Interpretation Chart, Houston
Texas
Schlumberger Limited, 1986, Log Interpretation Charts, Houston
Texas
Schlumberger Limited 1987, Log Interpretation Principles
Applications, Houston, Texas
Turcan A. N. 1966 Calculation of Water Quality from Electric Logs
-Theory and Practice, Louisiana Geol. Survey, Water
Resources Pamph. 19
Vonhoff, J.A., 1966 Water Quality Determination from Spontaneous
Potential Electric Log Curves, Amsterdam, Netherlands,
North-Holland Publishing Co., Jour. Hydrology v. 4
Welex, A Division of Haliburton Services 1968, Charts for
Interpretation of Well Logs, Houston, Texas
7-2
-------
FIGURES
-------
FIGURE 1 SALINITY - RESISTIVITY CHART
-------
BASIC MATERIAL
Resistivity of NaCl Solutions
E
£L
I
3
%
0
>.
1
J2
©
cr
125 tSO
50 6C 70
80 90-00
1 r—-1
300 ISO 400
140 ISO 1*5 JOO
Temptifatu.'i; ¦. "F w JC,
G«n-9
-------
FIGURE 2 NaCl - RESISTIVITY VS TDS CONCENTRATIONS
-------
1 1
k-rJiwa.Hi.uj
RESISTIVITY NOMOGRAPH FOR NaCI SOLUTIONS
R
(ilm)
.01
op
50-
60-
70-
80-
90-
100-
°C
10
150-
200-
250
300-
400-
500-
-20
¦-30
•40
-50
¦60
-80
-100
--120
•140
•160
-180
-200
•220
•240
-260
Conversion approximated by:
R,= R
/ T,+ 6.77
2" "i\ Tj* 6.77' (Arps)'
;°F
r2=r,(
or
T, + 21.5
Tj + 21.5
)-,°C
g/kg Grains/gai
or ®24]t
k ppm or75aF
300-q
-17500
200 -
-13000
= 10000
100;
-
80 2
— 5000
60 Z
-4000
-3000
40-
-
30 -
-2000
20-
10-
a
6
4-
3-
.8
.6'
.4
3'
-1000
•500
400
r3oo
200
rioo
50
40
30
20
(c) Schlumberger
-.02
-.03
-.04
•.05
-.06
-.08
-0.!
.2
.3
.4
.5
.6
.8
1.0
•3
4^6
|9
~r .
-4— | Q
|
£ 20
-------
FIGURE 3 FORMATION FACTOR VS POROSITY
-------
FORMATION FACTOR VERSUS POROSITY
10
9
8
* i 6 e to
20 50 40 50 60 80 100
200 300 400 600 tOOO
2000 3000 5000
10,000
-------
FIGURE 4 SP CORRECTION FACTOR VS BED THICKNESS CHART
-------
I
SP CORRECTION FACTOR vs. BED THICKNESS CHART
-------
FIGURE 5 EMPIRICAL SP CORRECTION CHART
-------
Empirical SP Correction Chart
SP correction factor
-------
FIGURE 6 MOD WEIGHT CORRECTIONS
-------
ieie
6
4 H
*# ; * •
Mud Cake, Mud Filtrate,
and Mud Resistivities
for Various Mud Weights
PURPOSE
One of the factors affecting a mud's other
properties is its weight. Resistivity charts usu-
ally do not consider such variables, although
they may be significant. The relationship of
mud weight and resistivity to the resistivities
of mud cakes and filtrates is shown here.
The data is taken from "A Correlation of the
Electrical Properties of Drilling Fluids with Sol-
ids Content," by Overton and Upson; Petro-
leum Transactions, AIME, TP 8045, 1958.
1J3
Rm s
.4
.2
.10
.08
.06
.04,
.04 .06.08.10
.2 .4 .6 .8 1.0
Rmc
4 6 8 10
APPLICATION
1. Determine Rmc at reservoir temperature
When: Rm = 1.3 ohm-meters
Mud Weight = 13 lbs./gal.
THEN: Rmc = 3.2 ohm-meters
2. Determine Rrrtf at reservoir temperature
When: Rm = 1.3 ohm-meters
Mud Weight = 13 lbs./gal.
THEN: Rmf = 0 65 ohm-meter
04 06 OS 10
Rmf
-------
FIGURE 7 ESTIMATION OF FORMATION TEMPERATURE
-------
Schlumberger
ESTIMATION OF FORMATION TEMPERATURE
(Linear Gradient Assumed)
Annual mean
surface temp.
4
27° 50
¦ '
Temperature, °C
100 125
0.6 !0.0 |!.0\L2 1.41 1.6 "F/100 ft
in
-------
FIGURE 8 Rw VS Rweq AND FORMATION TEMPERATURE
-------
ScMumberger
R. VERSUS R.„ AND FORMATION TEMPERATURE3
or Rmf
(H-m)
Use the solid lines of this chart for predominantly NaCI wafers. The dashed lines are approximate
for average'' fresh formation waters (where effects of salts other than NaCI became significant). The
dashed portions mav also be used for gyp-base mud filtrates.
EXAMPLE: R_, *= 0.025 at 150JF From chart, R. = 0.038
Spe cial procedures for muds containing (la or Mq in solution are discussed m she reference. uine-
buse r'nuds usijaily have a negligible amount jf Ca m solution, and may be *r rated .si rftjuior mud fypws.
-------
FIGURE 9 Rweq DETERMINATION FROM THE SSP
-------
Rweq DETERMINATION FROM THE SSP
(CLEAN FORMATIONS)
For predominantly sodium chloride muds determine RmfM| as follows:
a. ff Rmf at 75 °F (24° C) is greater than 0.1 Q*m, correct Rmf to formation
temperature using Gen-9, and use RM(W1 = 0.85 Rmf.
b. If Rmf at 75°F (24°C) is less than 0.1 Q*m, use SP-2 to derive a value
of °t formation temperature.
R
weq
.001
STATIC
SP
mV
-200-
¦180
160
-140
-120
-100
-80
-60
¦40
•20
+20
+ 40
Rmfeq /Rweq
.4
.6 --
.8
TV
£°>. °C
fPoffro
tOof'So
fOoJ*°o
T 5o
(C) Sehlumberger
8
10
20 -f
40--
60
80--
ioo i
(2)
¦SSP
•Kc!og
Rmf
Rw
Kc= 61 +.133 T("F)
Rmfeq
.01
DZ —
.04--
.06 +
.2—
.4+
.6
4-
6 ¦
10-
20'
40
60
IOO -
(3)
.005-
.01
.Q2C
.05
0.1
0.2
as
i.o
2.0*
(4)
Kc = 65 + 24I(°C)
SP-1
-------
FIGURE 10 RESISTIVITY SYMBOLS USED IN LOG INTERPRETATION
-------
FIGURE 10
| — RESISTIVITY OF THE ZONE
Q — RESISTIVITY OF THE WATER IN THE ZONE
Ken E. Davis
Associates
RESISTIVITY SYMBOLS USED
IN LOG INTERPRETATION
PATE; 12/14/87^
CHECKED BY; M/J |jQ8 NO.; 30~956
22
1 WO. N0.:3O-956~1
DRAIN BY. D. T.
APPROVED Wit
-------
APPENDICES
-------
APPENDIX 1
EXAMPLE X - CALCULATION OP TDS USING RP AND SP METHODS
-------
APPENDIX 1
CASE HISTORY - CLASS I DISPOSAL WELL
BRAZORIA COUNTY, TEXAS
Well Log Heading Data
BHT 294°F
TD 15000 ft
Mud Weight 11.4 ppg
Rm = 4.8 ohm - m @ 75°F
Rmf = not listed
1) Calculate TDS concentration at the suspected USDW, from
the clean sandstone interval between 1300 - 1360 ft
A) RP Method
1) Determine Porosity from Crossplot
<6 = 36% = 0.36
2) Determine Formation Temperature Using Figure 7
Tf = 99°F (with assumed surface temperature
of 80F)
3) Determine formation factor using Humble
equation or Figure 2
F = 0 .62/e52 "15
= Q'62 2 15
(-36) = 5^Z
4) Pick Ro from deep Electric Log
Ro = 3.1 ohm - m
5) Determine Rw using equation 2
Rw = Et
F
Rw = 3 .1 ohm - m = 0.56 ohm - m
5 .57
1
-------
6) Determine TDS concentration using Figures 1 or 9
TDS = 7700 ppm
II. B) SP Method
1) Determine formation temperature using Figure 6
Tf = 99°F
2) Determine Rm at formation temp, using Figure 1
and Rm value listed on log heading
Rm = 3.7 ohm - m @ 99°F
3) Determine Rmf at formation temp, using Figure 6
Rmf = 2.9 ohm - m
4) Pick a value for SSP (maximum deflection from
shale baseline)
SSP = -50 millivolts
5) Determine Rmfeq using equations in Figure 9
Rmfeq = 0.85 Rmf
= 0.85 (2.9 ohm - m)
= 2.5 ohm - m
6) Determine Rweq using Figure 9
Rweq = 4.5
Rweq = 0.57 ohm - m
7) Determine Rw from Rweq using Figure 8
Rw = .57 ohm - m
8) Determine TDS concentration using Figure 1 or 2
TDS = 7500 ppm
O
-------
APPENDIX 2
SUBSTANTIATING INFORMATION FOR SECTION 4.0
-------
*- w \ j'aJxruiin-iI&s wc. —
?9?9GSRi*ve. • BATON «OUGE. L* >08rt>
Lake Charles, Louisiana
May 27, 1985
Samole:
Qua!ity Assurance
Date/T ime
Parameter"
Results
Actual/Found
Analvst
Ch1 or ide {mq/L CI)
4,050
50.0/50.5
05 -23/0830/DT
Color (APHA Units) (True/Apparent)
25/100
50/50
05 -23/15 00/0 T
Iron (mg/L Fe)
2.3
0.50/0.49
05-24/RM
Manganese (mg/L Mn)
0.06
0.250/0.250
05-24/RM
Odor (T.O.N.)
No Odor Detected
Pos i ti ve
05-23/1500/DT
Sulfate (mg/L SC^)
7.9
10.0/9.1
05-24/0900/DT
Total Dissolved Solids (mg/L)
7,020
5,000/5,120
05-24/0800/KA
ilica (mg/L SiO-)
21
5.0/5.0
05-24/1500/RG
£
Calcium (mg/L Ca)
52
0.250/0.248
05-24/RM
Magnesium (mg/L Mg)
21
0.250/0.247
05-24/RM
Sodium (mg/L Na)
2,890
5.0/4.7
05-24/RM
Potassium (ma/L K)
7.5
5.0/4.3
05-24/RM
Total Phosphate (mq/L P)
0.26
0.50/0.47
05-25/1400/Ru
Total Orqanic Carbon (mq/L C)
5
25/23
05-23/0730/MS
Total Orqanic Haloqen (mg/L CI)
0.47
0.100/0.095
05-27/N8
Spec i fic Grav i ty
1.01
1.00/1.00
05 -24/1100/R G
-------
p
'EST-PA1NE
jaJxruxtmleA inc ,
<7^
Hrt CSBI **C • »*ION »OUGE. LA ?0M0
Lake Charles, Louisiana
Hay 21t 1985
Sample:
Parameter
pH (Units)
Specif lis: Oonducti v i ty (K)
Temperature (°C)
Arsenic (mg/L As)
Barium (mg/L Ba)
Cadmium (mg/L Cd)
Chromium (mg/L Cr)
Lead (mq/L Ph)
Mercury (mq/L Hq)
_,elenium (mg/L Se)
Silver (mg/L Agl
Nitrate (mq/L N)
Fluoride (mg/L*F)
Total Coliform (colonies/100 ml)
Turbidity (NTU)
Endrin (mg/L)
Lindane (mg/L)
Toxaphene (mg/L)
Methoxychlor (mg/L)
2,4-0 (mg/L)
2,4,5-TP Si ivex (mg/L)
Radium (pC 1/L)
Gross Alpha (pCi/L)
Gross Seta (pCi/t)
Carbonate Alkalinity (mg/L CaCO-j)
'icarbonate Alkalinity (mg/L CaCOj)
Results
7.59
13.5
25.3
0.06
1.6
0.01!
<0.01
<0.04
<0.0002
0.33
<0-01
0.03
1.0
3.0
20
<0.0002
<0.004
<0.005
<0.100
<0.100
<0.010
5.41 * 0.42
2.16 * 1.94
13.24 ~ 4.28
<1.0
550
Quality Assurance
Actual/Found
Analyzed
Analyzed
Analyzed
0.050/0.048
2.50/2.36
0.250/0.250
0.50/0.50
2.50/2.50
0.0100/0.0105
0.050/0.048
0.50/0.50
0.20/0.20
0.50/0.50
Positive
100/100
Not Applicable
Hot Applicable
Not Applicable
100/108
100/108
Date/Time
Analvst
In Field
In Field
In Field
05-23/VM
05-24/RM
05-23/VM
05-24/RM
05-24/RM
05-23/VM
05-23/VM
05-23/VM
05-24/G800/MS
Q5-25/1030/RG
05-23/1500/DT
05-23/1500/DT
05-24/CL
05-24/CL
• 05-24/CL
05-24/CL
05-24/CL
05-24/CL
Not Applicable
Not Applicable
Not Applicab le
05-24/1400/DT
05-24/1400/01
85-1889
J
-------
mujcanii
A CSU* Service
j
I
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. --
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y
C i
k*k ;
r r\
~ . ;
t"; •
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a < -
I 9 »
COMPANY,
EXHIBIT NO.
1
WEIL .
FIELD
COUNTY,
U. I C. MONITOR Wl'l I
t) I SI'ObAI
( Al CASH U
_STATE.
IOUI SI ANA
IB!/* i si h %»• rn or src. 3?
API hi KHI no src
Other Services:
Ptimantril Dolum:
Log Meaivred from
Dulling Meul^red from
fit
9.5
Elev.i
20.0
Elev.
SAMC
_fl. Above Perm. Datum
K.fl..
D.F..
G.L..
29.
?0.0
Dote
Run N o
Oepih Duller
Depth Logger tSthl
6t:Ti ta-g internet
Top tog Inieoal
Coiing Duller
Canc.g logger
8 i Sue
Type fl-ttJ m Hole
Dens. j Viic
pM I fluid Ij«
Source of Sample
Rm .i'{j Meal Temp.
' - f a, Meal Temp
R.tsc iu- Meat Temp
Source Rmf I ®mt
^TCircuialion Stopped
^i'logget on ftoliom
Mai. Rec. Temp.
locolion
Recorded By
W l.-.ened By mTSSI.
S 9 H
() Nt
Z?5.k
??Vj
12jZ_
64
!?
M
9 7/B
Qt'lf Kj
9.;
/ o
fT i
(ii
'j . fi 1 @76 f _
(2 • L1 _ ® ll 11
J
EILLEl_
4.01/ @ 90 -f
?no/s-9
5: 90
•f
con
B107__
HI S£ V
as. wrmi-roNr,ni
ml
ta>
*F
ml
*F
*F
@
•F
*F
@
X
"F
t3
:"X
y:
o
Q
-------
-------
APPENDIX 3
SINCLAIR VARIABLE MULTIPLIERS
-------
An example of this method using water-quality data for the Red River
Formation in a North Dalcota well is illustrated in table 1. The water
analysis is listed with the appropriate multiplier for each ionic constituent
(Desai and Moore,. 1969). The last column in Che cable lists the product of
ppm and the multiplier. The sum of che products is Che concentration of an
equivalent NaCl solution in ppm. Resistivity of this solution can be deter-
mined from nomograph 1-4 in Dresser Aclas (1979). The formula from Dresser-
Atlas (1979),
3647.5
Ru - 0.0123 + ,
[NaCl ppm]
can be used to calculate Rv, when Che cotal ppm as NaCl is less Chan
100,000 ppm. The calculated resistivity in cable 1 differs from Che measured
value by abouc 9 percenc. In most cases Che difference between Che calculated
and the measured resistivities will be less Chan plus or minus 10 percent, and
should be within plus or minus 5 percenc according co Desai and Moore (1969).
Table 1.—Analysis of water from drill-stem teszs in a North Dakota well
Sinclair
Constituent Concencracion variable Resulcanc
(ppm) multiplier (ppm)
Calcium
7,640
0.349
2,666
Magnesium
1,420
-.652
-926
Sodium
66,056
1.0
66,056
3icarbonace
60
.100
6
Sulfate
1,235
.200
24 7
Chloride
118,600
1.0
118,600
Dissolved solids calculated
194,380
Equivalenc NaCl
186,649
Specific gravity 1.129 g/cc
Measured resiscivicy 0.056 oha-mecers
Calculated resistivity (from
nomograph. Dresser-Aclas,
1979) 0.051 ohm-mecers
-------
APPENDIX 4
HINGLE CROSS PLOT
-------
HINGLE CROSSPLOT
INTRODUCTION
In the late !95G's, Hingle proposed a method based
on resistivity and porosity log data which allows the
percent water saturation to be determined directly
from a crosspiot. The method is based on the wefl-
known Archie equation, which in a rearranged form is
plotted on special grid-type graph paper.
The basic mathematical manipulation includes:
F = a/+™
Ro — Fx Rw
R<3 = SSr X Rt
4 = (a/F)1/tn
^ = [(a x Rw)/R0)]1/m
4 = [(a x Rw)/(Sw* x R,)J1/135
? = [(a x Rw)/Swn]I/m x R,J/m (I)
Equation 1 will describe a set of straight lines
fanning-out from a common point or origin when
plotting porosity, 4, v$ resistivity, Rt, the latter on a
special grid (i.e., Rt~1/m). Special graph paper is
required (Figures 23.2 and 23.3) for sandstones (where
F = 0.62 x $-2-15) and carbonates (where m = 2.0).
Figure 23.1 shows the basic principles of the Hingle
plot. Lines of constant Sw values originate at the
matrix point where porosity s = 0% and Rt = <*»,
provided formation water salinity stays constant over
the interval under study.
The water line (Sw = 1.0) can be drawn from the
matrix point through the most northwesterly points on
the crosspiot. The slope of this water line defines Rw,
which can be calculated by:
Rw = Ro/F (2)
anywhere along the water line (Sw « 1,0).
Sw lines other than for 1.0 can be determined based
on the Archie equation:
R, = Ro-'Sw: (3)
For example, 4 x R0 corresponds to the line of S„ =
0,5, 11 x R0 corresponds to S» ¦» 0.3, 25 x R0 to
0.2, etc. (Fig. 23.;)
Any of the three porosity logs (acoustic, density,
neutron) ;an be used with any deep-reading resistivity
Where:
Caroanates: P - *'m - *"J
Sancswnes: F - 0.S2 x »-1:5
12 - S„ 13 - 12 - Movable Oil (MOP)
13 - Sm 14 - 13 - Residual Oii(ROS)
FIGURE 23.1
Mingle plot pnnaptes.
device (induction, laterclog, etc.). Further, if an R*Q
device is available, the amount of movable oil (MOP)
can also be determined graphically. For the crosspiot,
the Rm value has to be corrected for the resistivity
contrast between formation water (Rw) and filtrate
(*W). This normalization is obtained by (R,0) *
(Rw/Rmf). The latter vaiue is then entered into the
crosspiot.
The basic response of the three porosity logs is well-
known and has been discussed many times in well log-
ging literature. These tool responses have to be kept in
mind when using the Hingle plot. Figure 23.4 shows
the generalized effects which may influence any inter-
pretative results.
Plotting procedure is outlined as follows:
1. Select proper crosspiot paper. (Fig. 23.2 or 23.3)
2. Scale the x-axis in linear fashion for raw logging
parameters (it. Ps) and establish porosity scale.
Porositv will be zero a: :he matrix pom: and in-
creates the 'tgh: Make sure the scale is \cxcie3
-------
Conductivity
2000
1500
1000-
C,
500-
300-
250
200.
150 ^
100-
I I I I I I
Resistivity
0.5
i i i i
i i i i
i i l I I i I I
I I I I
I I I I I I
i i i i r
o.s
o.r
o.a
1.0
1.2
1.5
i - a.-2
1.0-r 100%
R,
2.0 2.5-r-70
2.5
10
20-
ICQ '00'
i 50
4—.60
7--50
10-U4O
,30
40-(-20
10
a 62
- T7?»
FIGURE 23.2
vtJivtry/Pcrcs.ry s-ssseicis 'or ".jnasiO'"1*
-------
Sw = (F x Rw)/Rt, [SM = (F x Rmf)/R.x0],
MOP = Sxo - Sw
However, Rxo values have first to be normalized by
multiplying Rxo by the ratio Rw/RmJ- before being
plotted on the crossplot graph. The comparison of the
computed Sxo and Sw values is then indicative of the
amount of movable hydrocarbons.
FIELD EXAMPLES
Example 1
Table 23.1 lists pertinent logging data in a well drill-
TABLE 23.1
DENSITY — RESISTIVITY CROSSPLOT
Rw' Salinity
Variations
Lithology
Heavy Minerals
Effecs due to gas.
light hydrocarbons,
compaction shaliness.
njgosity. washouts.
Porosity
FIGURE 23.4
Generalized effects.
properly so the highest expected porosity values
will still plot on the graph paper.
3. Plot the resistivicy (RJ vs log data (At, P\5, 4^). The
resistivity scale can be changed by any order of
magnitude to fit the log data. This is done without
changing the validity of the graph paper grid.
4. The straight line drawn through the most north-
westerly points defines Sw = 1.0. Extrapolate this
to the intersection with x-axis = 0, R( = °°).
5. At the intersection determine the matrix value
(Atma or Pm3) for a proper porosity scaling of the
x-axis.
6. Calculate Rw from any corresponding set of | and
Ro data along the water line such as Rw » Rf constant Sw can be
drawn. .ii! f »n:cn ordinate :n Tia:r:x point.
-------
Conaucxivity Resistivity
t - 0 S3* '0°fl
Cor ti . 2.2)
Resistivity scale 5 reaucea by 'actor :Q
FIGURE 13.5
R*SlJ!tvlty/PorQ3,ry Croisowr (RPCP)
-------
« As can be seen in the crosspiot, only intervals 1,
2, 6, 8, 9 and 10 fail beiow the 50% Sw line.
Example 2
Table 23.2 lists pertinent logging data in a well drill-
ed with Fresh mud in the Rocky Mountain area. The
target formation is known to be a dolomite (Vra =
TABLE 23.2
(Weil Location: Rocky Mountain Area)
MOP
Depth,
a.
At
s*.
s»
S. -
No.
ft
2m
2m
m sec/ft
%
%
%
a.. %
1
x524
20.0
13.0
53
10.0
33
46
13
2
28
9.5
8.0
59
11.0
42
54
12
3
31
18.0
12.0
57
9.5
35
53
18
4
33
so.o
3S.0
55
a.o
25
35
10
5
x536
30.0
1S.0
53
9.0
29
47
18
23,000 ft/sec), and Rw = 0.02 Qm and Rmf = 0.23
Qm at formation conditions.
Knowledge of the above parameters is sufficient to
omit plotting the logging data, sines a straight forward
application of the Archie equation gives both Sw and
S,D; the water saturations in the uninvaded and
flushed regions around the wellbore.
Sw = (F x Rw)/Rt
Sxo = (F X Rnif}/Rxo
Furthermore, close inspection of the data in Table
23>2 clearly shows that reservoir porosity extends over
a very small range, which would make crossplots of
such data crowded and less advantageous. In other
words, logging data should be looked at prior to
blindly starting out with a particular crosspiot tech-
nique.
CONCLUSION
The H ingle crosspiot technique is a powerful
crossplotting technique which allows a long section of
well logs to be analyzed in a minimum of time. Similar
to any other formation evaluation technique the
Hingle method has several advantages and limitations.
Advantages include:
!• A matrix value does not have to be assumed. It is
determined from the crosspiot.
3. Quantitative Sw presentation, including visual
quick-look at potential pay sections.
4. Minimum calculations.
5. Well adapted for fresh and salt-mud logging.
6. With Rjo data a typical MOP evaluation is pos-
sible.
Limitations include: a relatively large range of
porosity is required; and shaly sands, unconsolidated
formations, gas effects, etc. require certain logging
suites and precautions. Also, formation water salinity
(i.e., Rw), Ethology, and degree of mud filtrate inva-
sion have to stay fairly constant over the interval of
interest. Finally, a water zone has to be present or a
tellable Rw value has to be known.
BIBLIOGRAPHY
Hingle, A. T. The Use of Logs in Exploration Prob-
lems, Transactions, Society of Exploration
Geophysicists, Los Angeles: 1959.
2. R„ value can be computed from the graph.
------- |