United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada, OK 74820
Research and Development
EPA/600/SR-93/021 May 1993
EPA Project Summary
Laboratory Study on the Use of
Hot Water to Recover Light Oily
Wastes from Sands
Eva L. Davis and Bob K. Lien
This laboratory research project in-
vestigated the use of hot water to re-
cover oily contaminants that are less
dense than water, highly viscous at
ambient temperatures, and essentially
nonvolatile. Displacement experiments
were conducted at constant tempera-
tures in the range from 10 to 50°C, and
an increase of approximately 17 to 22
percent in oil recovery was achieved.
The major mechanism for the increased
recovery appeared to be viscosity re-
duction. Transient temperature dis-
placement experiments were also
performed by placing the oil-saturated
column in the incubator at 10°C and
using water at 50°C to displace the oil.
The oil recovery from these experi-
ments was comparable to that found
for a 40°C constant temperature water-
flood. Capillary pressure-saturation
curves and the displacement experi-
ments showed that the residual water
saturation increases with temperature,
while the residual oil saturation de-
creases with temperature. Comparison
of the capillary pressure for a given
wetting phase saturation for different
fluid pairs and for different tempera-
tures show that the ratio of interfacial
or surface tensions cannot account for
changes in the capillary pressure
curves as the fluids and temperatures
are changed.
This Project Summary was devel-
oped by EPA's Robert S. Kerr Environ-
mental Research Laboratory, Ada, OK
74820, to announce key findings of the
research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back)
Introduction
Cases of soil and groundwater contami-
nation by organic liquids that are immis-
cible with water are numerous and involve
many different types of organic liquids.
The properties of these fluids, such as
density, volatility, viscosity, and water solu-
bility, vary significantly, and therefore dif-
ferent remedial techniques will be required
in dealing with these different contami-
nants. For oils that are viscous and non-
volatile, enhanced recovery using hot water
has been demonstrated in the laboratory
by researchers in the petroleum industry,
and this technique has been used at vari-
ous field sites.
The purpose of this research project is
to investigate the use of moderately hot
water for the displacement of oily con-
taminants from the subsurface. The ex-
pectation is that the heat source will be
waste heat from an industrial process,
which will limit the injection temperature of
the water to approximately 50°C. A litera-
ture review was conducted into the effects
of porous media and fluid properties on
the displacement of oil by water and the
effects of heat on the displacement pro-
cess. Laboratory experiments were con-
ducted to study the effects of heat on the
capillary pressure-saturation relations and
displacement process, and numerical simu-
lations were run in an attempt to model
the results.
Experimental Materials and
Methods
The oil phase used for these experi-
ments was Inland 15 Vacuum Pump Fluid,
and distilled water was used for the dis-
placing fluid. The viscosity of the oil, its
density, and its surface and interfacial ten-
Printed on Recycled Paper
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sion were measured over the range of
temperatures of interest. Two different
silica sands were used for the porous
media. The first sand, referred to as 20/30
sand, has a very uniform grain size distri-
bution with all grains passing the #20 sieve
but retained on the #30 sieve, making all
grains in the range of 0.85 to 0.60 mm.
The second sand was a mixture of three
size ranges of sands, giving one third (by
weight) of the grains in each of the size
ranges of 0.85 to 0.50 mm, 0.50 to 0.25
mm and 0.25 to 0.106 mm. This sand is
referred to as the mixed sand.
Three types of experiments were per-
formed. Capillary pressure-saturation
curves were determined for each of the
sands for water-air and water-oil. The pres-
sure-saturation relations were determined
at the constant temperatures of 10 and
30°C. The other two types of experiments
were constant temperature displacement
experiments in the range of 10 to 50°C
and transient temperature displacements
where the oil-saturated column was held
in an incubator at 10°C and water at 50°C
was used to displace the oil. All displace-
ment experiments were performed with
one-dimensional stainless steel columns.
The soil columns were initially fully satu-
rated with water, which was displaced by
oil. The oil was then displaced by water.
The column effluent was collected in a
fraction collector so that the fraction of oil
in the effluent versus the amount of water
injected could be determined. The pres-
sure at each end of the column was mea-
sured throughout the displacements. The
constant temperature displacements pro-
vided information on the flow properties of
the sands and fluids at each of the tem-
peratures, while the transient temperature
experiments more closely modelled the
hot water displacement that would occur
in the field.
Experimental Results and
Discussion
The capillary pressure-saturation curves
for the water/air systems show that tem-
perature has a significant effect on the
these curves. The increase in tempera-
ture from 10 to 30°C caused a decrease
of approximately 30 percent in the dis-
placement pressure for these curves and
caused an increase in the residual water
saturation in the 20/30 sand. The residual
saturation of the mixed sand was essen-
tially the same at each temperature. The
pressure-saturation curves measured for
the water/oil systems essentially did not
change over the temperature range of 10
to 30°C, other than changes in the re-
sidual water and oil saturations. Compari-
son of the water/air to water/oil curves for
each of the sands showed that the water/
oil curves were significantly different from
the water/air curves. The Brooks-Corey
(1964) and van Genuchten (1980) equa-
tions were fit to these curves, and using
these equations the relative permeability
to each phase as a function of saturation
could be predicted.
The constant temperature displacement
experiments showed an increase in oil
recovery of about 17 to 22 percent as the
temperature was increased from 10°C
(which was considered ambient tempera-
ture) to 50°C. The greatest increases in
oil recovery were found at breakthrough,
with increases as great as 30 to 50 per-
cent. The mixed sand always showed a
greater oil recovery than the 20/30 sand.
The oil saturation remaining in the column
after the injection of 10 pore volumes of
water was about 39 percent for the 20/30
sand at 10°C, and 30 percent at 50°C.
For the mixed sand, the oil remaining af-
ter the injection of 10 pore volumes of
water was 33 percent at 10°C and 23
percent at 50°C. Thus, the increased tem-
perature reduced the oil remaining in the
column by 25 to 30 percent.
These remaining oil saturations are sig-
nificantly greater than the residual oil
saturations found in the capillary pres-
sure-saturation curves. Considering the
water to oil ratio of the effluent at the
end of the displacement experiments, an
additional 16 to 20 pore volumes of wa-
ter would have to be injected to reduce
the oil saturation in the columns to the
true residual.
Pressure measurements recorded dur-
ing these displacements showed that the
maximum pressure during the displace-
ment occurred at the time of water break-
through, i.e., as the water reached the
effluent end of the column. As the tem-
perature increased, the pressures in the
column and the pressure drop along the
column decreased significantly.
The transient temperature experiments
were run to more closely model the dis-
placement process that would occur in
the field. Water at 50°C was used to dis-
place oil at 10°C from the column, while
the system was held in a constant tem-
perature incubator. The temperature in the
column was monitored at 4 locations along
the column during the displacement. The
temperature at any location remained at
10°C until the hot water front reached it,
then the temperature rose quite rapidly to
its equilibrium temperature. At the influent
end of the column, the column reached at
maximum temperature of about 37 to 39°C,
and the equilibrium temperature along the
column dropped off linearly along the col-
umn to about 30°C close to the effluent.
Undoubtedly, the stainless steel column
used for these experiments moved heat
away from the sand faster than would
occur in a field situation because of the
significantly higher thermal diffusivity of
stainless steel compared to that of silica
sand. Attempts to insulate the column to
reduce the heat loss increased the tem-
perature along the column by approxi-
mately 2°C but did not appear to
significantly affect oil recovery.
Despite the fact that the heat essen-
tially did not travel in front of the hot water
front, the benefits of the increased tem-
perature were realized in terms of the oil
recovery. The percent oil recovery at the
time of water breakthrough was not sig-
nificantly increased, but the oil recovery
after water breakthrough was increased.
The final oil saturation after the injection
of approximately 10 pore volumes of wa-
ter was similar to that achieved in the
40°C constant temperature water-floods.
The pressure drop at the time of water
breakthrough for the transient tempera-
ture displacement experiments was simi-
lar to that measured in the 10°C constant
temperature displacements. After water
breakthrough, the pressure drop along the
column decreased quickly to a level com-
parable to a 40°C waterflood. Thus, the
benefits of hot water in terms of the pres-
sure required to drive the displacement
process was not realized until after water
breakthrough.
From the data of oil recovery versus
volume of water injected for the constant
temperature displacement experiments, the
ratio of oil permeability to water perme-
ability can be calculated for the range of
saturations in the column between water
breakthrough and the end of the displace-
ment by the method of Welge (1952).
These calculations showed that the per-
meability ratio at low water saturations is
shifted to higher values as the tempera-
ture is increased. As the water saturation
is increased beyond about 0.4 to 0.5, the
ratio of permeabilities tend to merge to
the same line. The relative permeability to
oil and to water was also be calculated by
the graphical technique developed by
Jones and Roszelle (1978), which is
equivalent to the technique developed by
Johnson et al. (1959). The relative
permeabilities calculated by this method
show that the relative permeability to
each phase tends to increase as the
temperature increases, but the perme-
ability ratios calculated from these indi-
vidual permeabilities do not change with
temperature. The permeability ratios cal-
-------
culated based on the method of Jones
and Roszelle (1978) are significantly lower
than the ratios calculated based on the
method of Welge (1952). It is not possible
to tell at this time which technique gives
the more accurate ratios.
Simulation of Constant Tempera-
ture Experiments
Attempts were made to simulate the
constant temperature displacements us-
ing the Buckley-Leverett (1941) equation
for two-phase flow. Using this equation,
the amount of oil recovered from the col-
umn as a function of the amount of water
injected can be calculated. Input needed
for the calculation is the viscosity ratio of
the fluids and the relative permeability of
each fluid as a function of saturation. The
permeability ratios were calculated based
on the methods of Welge (1952) and Jones
and Roszelle (1978) and on the Brooks-
Corey (1964) and van Genuchten (1980)
equations fit to the capillary pressure-satu-
ration curves. None of these permeability
ratios were able to accurately simulate the
oil recovery history found in the displace-
ment experiments. Some qualitative infor-
mation, however, can still be gained from
these simulations. Comparison of the re-
sults of the experiments with the simula-
tion results when permeability ratios
corresponding to a 10°C displacement are
used with the smaller viscosity ratios found
at higher temperatures shows that the in-
creased recovery at higher temperatures
found in the laboratory displacements are
greater than can be accounted for based
on the decrease in viscosity ratio alone.
Simulations using the permeability ratios
determined at higher temperatures shows
that this increase in recovery is likely due
to shifts in the permeability ratios with
temperature.
Conclusions
These experiments have shown that the
use of hot water will increase the recovery
of oils from sands over that which can be
recovered using a waterflood at ambient
temperatures. The increase in oil recovery
found over the moderate temperature
range studied here was approximately 17
to 22 percent. This reduced the residual
oil saturation remaining in these sands
after 10 pore volumes of water throughput
by approximately 25 to 30 percent. How-
ever, even the residuals of 23 to 30 per-
cent of the pore space found in 50°C
constant temperature displacements would
probably require additional treatment.
The wide range of contamination prob-
lems facing those involved in subsurface
restoration will require a variety of
remediation techniques in order to deal
with the problems effectively and efficiently.
Thermal methods such as hot water dis-
placements of oily contaminants is one
technique which should be useful in the
recovery of an oily phase that is viscous
and essentially nonvolatile. A major ad-
vantage of hot water is that it does not
require the addition of new, potentially toxic
chemicals to the subsurface.
References
Brooks, R. H., and A. T. Corey, Hydrau-
lic Properties of Porous Medium, Hy-
drology Paper, #3, Colorado State
University, Fort Collins, CO, March
1964.
Johnson, E. F., D. P. Bossier, and Y. O.
Nauman, Calculation of relative per-
meability from displacement experi-
ments, Trans. AIME, 216, 1959.
Jones, S. C., and W. O. Roszelle,
Graphical techniques for determining
relative permeability from displace-
ment experiments, J. of Pet. Tech ,
30(5):807-817, 1978.
van Genuchten, M. Th., A closed-form
equation for predicting the hydraulic
conductivity of unsaturated soils, Soil
Sci. Soc. Am. J., 44:892-898, 1980.
Welge, H. J., A simplified method for
computing oil recovery by gas or wa-
ter drive, Trans. AIME, 91-98, 1952.
•&U.S. GOVERNMENT PRINTING OFFICE: 1993 - SSO-O67/SO130
-------
Eva L Davis (also the Project Officer, see below) and Bob K. Lien are with Robert
S. Kerr Environmental Research Laboratory, Ada, OK 74820
The complete report, entitled "Laboratory Study on the Use of Hot Water to Recover
Light Oily Wastes from Sands," (Order No. PB93-167906; Cost: $19.50; subject
to change) will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
Robert S. Kerr Environmental Research Laboratory,
U.S. Environmental Protection Agency
Ada, OK 74820
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-93/021
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