U.S. patent application number 13/932986 was filed with the patent office on 2015-01-01 for enhanced oil recovery using seawater and edta.
The applicant listed for this patent is KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS. Invention is credited to HASAN SALMAN AL-HASHIM, MOHAMMED ATTIA GADALLAH, Mohamed Ahmed Nasr El-Din Mahmoud, ABDULLAH SAAD SULTAN.
Application Number | 20150000916 13/932986 |
Document ID | / |
Family ID | 52114477 |
Filed Date | 2015-01-01 |
United States Patent
Application |
20150000916 |
Kind Code |
A1 |
Mahmoud; Mohamed Ahmed Nasr El-Din
; et al. |
January 1, 2015 |
ENHANCED OIL RECOVERY USING SEAWATER AND EDTA
Abstract
The enhanced oil recovery using seawater and EDTA
(ethylenediaminetetraacetic acid) is a method that uses injection
of EDTA in seawater to enhance the recovery of oil from sandstone
reservoirs. The EDTA may be introduced into seawater during the
initial extraction of oil from the reservoir by seawater injection,
or a solution of EDTA in seawater may be used to flush residual oil
from the reservoir after the initial extraction by seawater
injection. In either case, the EDTA is present in about 1.0 wt % to
about 5.0 wt % of the seawater solution, and the solution has a pH
of between 10.5 and 11.0.
Inventors: |
Mahmoud; Mohamed Ahmed Nasr
El-Din; (Dhahran, SA) ; AL-HASHIM; HASAN SALMAN;
(DHAHRAN, SA) ; SULTAN; ABDULLAH SAAD; (DHAHRAN,
SA) ; GADALLAH; MOHAMMED ATTIA; (DHAHRAN,
SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS |
Dhahran |
|
SA |
|
|
Family ID: |
52114477 |
Appl. No.: |
13/932986 |
Filed: |
July 1, 2013 |
Current U.S.
Class: |
166/305.1 |
Current CPC
Class: |
E21B 43/20 20130101 |
Class at
Publication: |
166/305.1 |
International
Class: |
E21B 43/20 20060101
E21B043/20 |
Claims
1. A method for enhanced oil recovery from a sandstone oil
reservoir, comprising the step of injecting a solution consisting
of an effective amount of ethylenediaminetetraacetic acid (EDTA) in
seawater into the reservoir for chelating cations in the formation
brine to prevent scaling caused by mixing the seawater with the
formation brine.
2. The method for enhanced oil recovery according to claim 1,
wherein the effective amount of EDTA comprises about 1 wt %
EDTA.
3. The method for enhanced oil recovery according to claim 1,
wherein the effective amount of EDTA comprises about 5 wt %
EDTA.
4. The method for enhanced oil recovery according to claim 1,
wherein the solution has a pH of about 11.
5. The method for enhanced oil recovery according to claim 1,
wherein the step of injecting the solution comprises injecting the
solution for the initial recovery of oil from the reservoir.
6. The method for enhanced oil recovery according to claim 1,
wherein the step of injecting the solution comprises injecting the
solution containing the EDTA after the initial recovery of oil from
the reservoir by seawater flooding in order to recover residual oil
from the reservoir.
7. A method for enhanced oil recovery from a sandstone oil
reservoir, comprising the step of injecting a solution consisting
of between 1 wt % and 5 wt % ethylenediaminetetraacetic acid (EDTA)
in seawater into the reservoir, the solution having a pH of about
11.
8. The method for enhanced oil recovery according to claim 7,
wherein the solution comprises 1 wt % EDTA.
9. The method for enhanced oil recovery according to claim 7,
wherein the solution comprises 5 wt % EDTA.
10. The method for enhanced oil recovery according to claim 7,
wherein the step of injecting the solution comprises injecting the
solution for the initial recovery of oil from the reservoir.
11. The method for enhanced oil recovery according to claim 7,
wherein the step of injecting the solution comprises injecting the
solution containing the EDTA after the initial recovery of oil from
the reservoir by seawater flooding in order to recover residual oil
from the reservoir.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the enhancement of oil
recovery in oil reservoirs, and particularly to enhanced oil
recovery using seawater and EDTA (ethylenediaminetetraacetic acid)
that enhances oil recovery in seawater injection systems by adding
EDTA to the seawater.
[0003] 2. Description of the Related Art
[0004] One method of enhancing oil recovery from oil reservoirs
involves injecting water into the reservoir. In many areas,
seawater provides the most economical and abundant source of water.
However, seawater contains sulfates, which can precipitate calcium
sulfate and other insoluble or slightly soluble sulfates from
minerals in the formation brine of sandstone reservoirs. These
sulfates develop into formations of scale, which constrict the
injection and pumping equipment, reducing the recovery of oil and
requiring shutdown to clean or replace machinery. Various attempts
are being used to improve oil recovery in reservoirs that use
seawater injection, e.g., by diluting the seawater with fresh water
to form "smart water" or low salinity water. Nevertheless, there is
still a need for cost effective methods of enhancing oil recovery
from oil reservoirs using seawater injection systems, particularly
in regions where fresh water is a scarce and valuable
commodity.
[0005] Thus, enhanced oil recovery using seawater and EDTA solving
the aforementioned problems is desired.
SUMMARY OF THE INVENTION
[0006] The enhanced oil recovery using seawater and EDTA
(ethylenediaminetetraacetic acid) is a method that uses injection
of EDTA in seawater to enhance the recovery of oil from sandstone
reservoirs. The EDTA may be introduced into seawater during the
initial extraction of oil from the reservoir by seawater injection,
or a solution of EDTA in seawater may be used to flush residual oil
from the reservoir after the initial extraction by seawater
injection. In either case, the EDTA is present in about 1.0 wt % to
about 5.0 wt % of the seawater solution, and the solution has a pH
of between 10.5 and 11.0.
[0007] These and other features of the present invention will
become readily apparent upon further review of the following
specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a graph showing a comparison of the oil recovery
factor for core flooding experiments performed at a temperature of
100.degree. C. at a rate of 0.25 mL/min in Berea sandstone cores
between a control seawater sample, a solution of seawater with 1.0
wt % ethylenediaminetetraacetic acid (EDTA), and a solution of
seawater with 5.0 wt % EDTA, each of the examples showing initial
extraction of oil from the sandstone cores.
[0009] FIG. 2 is a graph showing the oil recovery factor for core
flooding experiments performed at a temperature of 100.degree. C.
at a rate of 0.25 mL/min in 3-inch Berea sandstone cores by a
solution of seawater with 5.0 wt % EDTA, showing the recovery of
residual oil after initial seawater flooding.
[0010] FIG. 3 is a graph showing the oil recovery factor for core
flooding experiments performed at a temperature of 100.degree. C.
at a rate of 0.25 mL/min in 5-inch Berea sandstone cores by a
solution of seawater with 5.0 wt % EDTA, showing the recovery of
residual oil after initial seawater flooding.
[0011] FIG. 4 is a graph showing the oil/rock contact angle as a
function of pH of a core flooding solution.
[0012] FIG. 5 is a graph showing the oil recovery factor for core
flooding experiments performed at a temperature of 100.degree. C.
at a rate of 0.25 mL/min in Berea sandstone cores by a solution of
seawater with 5.0 wt % EDTA and with a pH of 12.2, showing the
recovery of residual oil after initial seawater flooding.
[0013] Similar reference characters denote corresponding features
consistently throughout the attached drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] The enhanced oil recovery using seawater and EDTA
(ethylenediaminetetraacetic acid) is a method that uses injection
of EDTA in seawater to enhance the recovery of oil from sandstone
reservoirs. The EDTA may be introduced into seawater during the
initial extraction of oil from the reservoir by seawater injection,
or a solution of EDTA in seawater may be used to flush residual oil
from the reservoir after the initial extraction by seawater
injection. In either case, the EDTA is present in about 1.0 wt % to
about 5.0 wt % of the seawater solution, and the solution has a pH
of between 10.5 and 11.0. The method is demonstrated by the
following experiments.
[0015] As a control, untreated seawater with a high sulfate content
was injected into a Berea sandstone core, which was initially
saturated with a composition that simulates a typical formation
brine. The contents of the seawater and the connate water (water
that is trapped in the pores of sedimentary rocks, i.e., formation
brine) are shown below in Table 1. Calcium sulfate in mineral form
was found to have precipitated in the sandstone core, as
expected.
TABLE-US-00001 TABLE 1 Composition of Seawater and Formation Brine
(Connate Water) Connate Water Ions (ppm) Seawater (ppm) Sodium
59,491 18,300 Calcium 19,040 650 Magnesium 2,439 2,110 Sulfate 350
4,290 Chloride 132,060 32,200 Bicarbonate 354 120 TDS 213,734
57,670
[0016] Core flooding experiments were performed using Berea
sandstone cores, each core having a diameter of 1.5 inches and a
length of either 3 or 6 inches. The permeability of the cores was
each approximately 100 mD, and porosity was approximately 18%. All
the experiments were performed at 100.degree. C. Formation brine
(i.e., connate water) having the properties shown above in Table 1
was injected through the cores, and then oil was injected to
stabilize the initial water saturation S.sub.wi under a back
pressure of 2,000 psi. The difference between the overburden
pressure and the injection pressure (i.e., the effective stress)
was kept constant at 500 psi. The flow rate was 0.25 mL/min through
the different flooding stages. Seawater was injected to recover the
oil from the three and six inches core samples.
[0017] Core flooding experiments were then performed with a
chelating fluid formed from a solution of seawater having the
composition shown in Table 1 and 1.0 wt %
ethylenediaminetetraacetic acid (EDTA, in the form of the sodium
salt, Na.sub.4EDTA) added to the seawater, and then a solution of 5
wt % EDTA in seawater to test the effect of the concentration of
EDTA. The EDTA was used both to recover residual oil after seawater
flooding, and to enhance the recovery of oil during the initial
seawater flooding. The pH values of the different flooding fluids
are shown in Table 2.
TABLE-US-00002 TABLE 2 pH Values of Different Flooding Solutions
Solution pH Seawater 7.50 1.0 wt % EDTA + Seawater 10.5 5.0 wt %
EDTA + Seawater 11
[0018] FIG. 1 shows the recovery of oil from the core flooding
experiments using three different fluids at 100.degree. C. and 0.25
mL/min for the recovery of oil during the initial flooding of the
cores. The recovery factor from the control seawater was 40%, and
the recovery factor from the 1.0 wt % EDTA solution was 46%. The
increase in the recovery from 40 to 46% that was achieved by the
addition of EDTA was due to the cation exchange between the rock
surface and the solution, and also the pH increase by 2.35 units,
from the seawater value of 7.5 to 9.85 (for the EDTA solution).
Increasing the pH reduces the interfacial tension (IFT) of the
solution. Adding EDTA at a concentration of 5.0 wt % gave a 47%
recovery. This 1% increase in recovery over the 1.0 wt % solution
is due to the increase in chelation, which increased the viscosity
of the solution. This effect is detailed below in Table 3.
Increasing the solution viscosity will control the mobility of the
injected fluid, and this mobility control increased the recovery by
1%.
TABLE-US-00003 TABLE 3 Viscosity and Density of 5.0 wt % EDTA
Solution Prepared in De-ionized Water at 70.degree. F. Calcium
Concentration (ppm) Viscosity (cP) Density (g/mL) 0 1.45 1.101 5000
1.64 1.115 10000 1.98 1.134 20000 2.14 1.187 30000 2.67 1.221
[0019] FIG. 2 shows the recovery of oil from the core flooding
experiments using first, initial recovery of oil by seawater
flooding, followed by second, recovery of residual oil from the
core by the 5.0 wt % EDTA solution in seawater at 100.degree. C.
and 0.25 mL/min in the three-inch long cores. Seawater alone was
able to recover 54% of the initial oil, and the EDTA solution
recovered an additional 7% of the residual oil. The same experiment
was repeated using the six-inch long cores, and the recovery
increased almost by the same percentage, as shown in FIG. 3.
[0020] Table 4 below shows the interfacial tension (IFT) of Arabian
light oil measured as a function of pH. Increasing the solution pH
decreases the IFT between oil and rock. In the present method, the
pH of the solution is 11. By utilizing a high pH solution, oil
recovery is enhanced by a decrease in the IFT. Additionally, it was
found that the contact angle was greatly affected by the pH of the
flooding fluid, as illustrated in FIG. 4. Increasing the pH of the
solution to 11 can decrease the contact angle to 70.degree., which,
in terms of wettability, is a water-wet state. The high pH (of
about 11) of the present EDTA solutions aids in changing the
wettability to more water-wet and reduces the IFT, thus allowing
for greater oil recovery.
TABLE-US-00004 TABLE 4 IFT of Arabian Light Oil at Varying pH
Values pH IFT (N/m) 2 15.8 3 17 4 20.2 4.5 17.8 5.1 20 7 13.9 9.21
5.4 10 5.2 13 0.1
[0021] It is thought that the addition of EDTA acted in a manner
similar to low salinity water flooding, forcing the rock to release
cations to replace the cation shortage in the flooding solution,
thus changing the wettability to a greater water-wet state.
Further, the EDTA acted as a surfactant, since it contains four
carboxylic groups, thus reducing the interfacial tension of the
seawater. Additionally, the viscosity of the EDTA rises when it
chelates cations from the solution, and this increases the
viscosity of seawater and aids in controlling the mobility of
injected water. Importantly, the EDTA leaches all calcium in the
solution, thus eliminating the possibility of calcium sulfate
precipitation and maintaining the injectivity in the reservoir at a
constant level.
[0022] FIG. 5 shows the oil recovery factor for core flooding
experiments performed at a temperature of 100.degree. C. at a rate
of 0.25 mL/min in Berea sandstone cores by a solution of seawater
with 5.0 wt % EDTA and with an increased pH of 12.2, showing the
recovery of residual oil after initial seawater flooding. Recovery
of 29% of the original oil in place and almost 75% of the residual
oil after sea water flooding was attained by injecting 5 PV of EDTA
(pH 12.2). The increase in oil recovery compared to the previous
cases can be attributed to the high pH value of the EDTA in this
case.
[0023] It is to be understood that the present invention is not
limited to the embodiments described above, but encompasses any and
all embodiments within the scope of the following claims.
* * * * *