U.S. patent application number 14/658483 was filed with the patent office on 2016-03-10 for gelling agent for water shut-off in oil and gas wells.
The applicant listed for this patent is KUWAIT INSTITUTE FOR SCIENTIFIC RESEARCH. Invention is credited to SHAWQUI M. LAHALIH.
Application Number | 20160068737 14/658483 |
Document ID | / |
Family ID | 53491914 |
Filed Date | 2016-03-10 |
United States Patent
Application |
20160068737 |
Kind Code |
A1 |
LAHALIH; SHAWQUI M. |
March 10, 2016 |
GELLING AGENT FOR WATER SHUT-OFF IN OIL AND GAS WELLS
Abstract
The gelling agent for water shut-off in oil and gas wells is a
composition that forms a gel to reduce or eliminate the flow of
water in a gas or oil well. The composition is formed by mixing
polyvinyl alcohol, a polyvinyl alcohol copolymer, or mixtures
thereof with an amino-aldehyde oligomer, such as urea formaldehyde
or melamine formaldehyde, with or without a cross-linker. The
polymer composition can be used to minimize or completely shut off
excess water production with insignificant reduction in hydrocarbon
productivity.
Inventors: |
LAHALIH; SHAWQUI M.; (SAFAT,
KW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KUWAIT INSTITUTE FOR SCIENTIFIC RESEARCH |
SAFAT |
|
KW |
|
|
Family ID: |
53491914 |
Appl. No.: |
14/658483 |
Filed: |
March 16, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14483068 |
Sep 10, 2014 |
9074125 |
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14658483 |
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Current U.S.
Class: |
507/230 |
Current CPC
Class: |
C09K 8/887 20130101;
C09K 8/882 20130101; C09K 8/5083 20130101; C09K 8/885 20130101;
C09K 8/42 20130101; C09K 8/512 20130101 |
International
Class: |
C09K 8/42 20060101
C09K008/42 |
Claims
1.-12. (canceled)
13. A process for preparing a polymer composition for retarding
fluid flow of water from subterranean oil and gas reservoirs,
comprising the steps of: (a) dissolving a water soluble polymer
selected from the group consisting of polyvinyl alcohol, a
copolymer of polyvinyl alcohol, and mixtures thereof in an aqueous
solvent to obtain a solution of the water soluble polymer having a
concentration between 10%-12% weight/volume; (b) preparing an
aqueous solution of an amino aldehyde oligomer having a
concentration between 40% and 85% weight/volume; (c) mixing the
amino aldehyde oligomer solution with the water soluble polymer
solution to obtain a gel-forming composition having a ratio of
oligomer to water soluble polymer between 60:40 and 80:20
weight/weight; and (d) diluting the gel-forming composition with
the aqueous solvent to obtain a polymer concentration between 6.25%
and 48% weight/volume.
14. The process for preparing a polymer composition according to
claim 13, wherein said water soluble polymer comprises polyvinyl
alcohol having an average molecular weight between 15,000 and
146,000 and said amino aldehyde oligomer comprises
urea-formaldehyde.
15. The process for preparing a polymer composition according to
claim 13, wherein said aqueous solvent is selected from the group
consisting of deionized water, brine, sea water, and tab water.
16. The process for preparing a polymer composition according to
claim 13, further comprising the step of adding a cross-linking
agent to the gel-forming composition, the cross-linking agent being
selected from the group consisting of boric acid, acetic acid,
borax, ammonium chloride, ammonium sulfate, glyoxal, and
glutardialdehyde.
17-19. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to polymer gels, and
particularly to a gelling agent for water shut-off in oil and gas
wells that enables retarding the fluid flow of water from
subterranean oil and gas reservoirs using gel compositions formed
by crosslinking water soluble polymers (such as polyvinyl alcohol)
with urea-formaldehyde oligomer.
[0003] 2. Description of the Related Art
[0004] Normally, when oil reservoirs become mature, most oil
reservoirs produce water mixed with oil in their production
lifetime. In some cases, even though substantial flows of
hydrocarbons have been shown, water production is so great and
water disposal costs so high that hydrocarbon production is not
economical. Therefore it is desirable to find a way to reduce or
shut off the flow of water while permitting hydrocarbon production
to continue.
[0005] If the water production is reduced by some treatment (such
as polymer gels) for water shut-off, then this might have a
positive effect on increasing oil production. The excessive water
production causes many problems and becomes very costly when the
water cut increases. Water production could be a result of many
reasons, including weak formation due to fractures connecting the
water zone with the oil-producing zone. It can also be caused by
water coning, which is the most common case, due to the high
pressure differential between water and oil zones. Other factors
that may cause water production include micro-cracks in cement
sheet, closeness of perforations to the water zone, and high
oil/water viscosity ratio, among other things.
[0006] For radial flow, where there are no fractures in the oil or
gas well, the polymer gel material could be considered effective if
it can reduce the permeability to water by more than a factor of
ten and preferably by more than a factor of twenty. At the same
time, the gel must reduce permeability to oil by less than a factor
of two, if oil zones are not protected during placement. There is
no universal treatment method to treat excessive water production
in producing oil wells. However, several techniques were developed
and used, which include: mechanical isolation of the
water-producing zone, use of gravel packing or placing of cement
plugs inside the casing, or the use of cement squeeze, or finally,
the use of inorganic gels (such as sodium silicate) or organic
polymeric gel systems.
[0007] The non-polymeric systems, e.g., cement squeeze, were used
and reported by some researchers with some limited success. The use
of inorganic gels, e.g., sodium silicate with hydrochloric acid,
was tried by many researchers, also with some limited success.
Organic polymer gel systems have also met with limited success.
[0008] Thus, a gelling agent for water shut-off in oil and gas
wells solving the aforementioned problems is desired.
SUMMARY OF THE INVENTION
[0009] The gelling agent for water shut-off in oil and gas wells is
a composition that forms a gel to reduce or eliminate the flow of
water in a gas or oil well. The composition is formed by mixing
polyvinyl alcohol, a polyvinyl alcohol copolymer, or mixtures
thereof with an amino-aldehyde oligomer. The polymer composition
can be used to minimize or completely shut off excess water
production with insignificant reduction in hydrocarbon
productivity.
[0010] The gelling agent is prepared by dissolving the PVA at a
concentration of 10%-12%; preparing a solution of the
amino-aldehyde oligomer at a concentrations of 40% to 85%; adding
the PVA solution to the amino aldehyde oligomer in a ratio of 10%
to 50% by weight of the final polymer composition; optionally
adding a cross-linker either before injection or after injection of
the final polymer composition into the well in a subterranean
formation; adding a retarder, if needed, to delay the gel time of
the polymer composition; and optionally adding an accelerator to
accelerate the gel time of the polymer composition.
[0011] These and other features of the present invention will
become readily apparent upon further review of the following
specification.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] The gelling agent for water shut-off in oil and gas wells
combines an amino-aldehyde oligomer with a water-soluble polymer
(polyvinyl alcohol (PVA)) and other optional additives, such as
dispersing agents, either with or without cross-linking agents. The
cross-linking agents (if present) include, but are not limited to,
hydrochloric acid, boric acid, borax, acetic acid,
toluene-P-4-sulfonic acid, glycol, glutardialdehyde, ammonium
sulfates, ammonium chlorides, and others. As described below,
various polymer compositions were prepared from these components
with different solution concentrations. Also, various cross-linking
agents were sometimes used at different concentrations in the final
polymer compositions. Tests were carried out to determine the most
important properties of these polymeric gels, namely, the
viscosity, the gelation time, the gel type and gel strength, the
relative thermal stability of these gels at various elevated
temperatures and their tendency to synerese at longer ageing time
at elevated temperatures and shrink and produce water. Finally, the
performance of these gelants/gels was evaluated for their ability
to effect water shut-off with significant results in reducing or
eliminating water production with insignificant reduction in
hydrocarbon productivity.
[0013] The polymer composition can be prepared aboveground prior to
its injection into the zone to be treated with the needed
properties in terms of gel time, gel strength and gel stability at
reservoir conditions. The polymer gelants/gels can significantly
reduce water productivity with minimal impact in oil and gas
production when they are injected in oil and gas wells, with and
without zone isolation.
[0014] The polymer composition is self-cross-linkable and comprises
multi-component polymers, chemicals and additives including, but
not limited to, a water soluble polymer, such as polyvinyl alcohol
(PVA) with molecular weight between 15,000 g/mol to 146,000 g/mol
and with degree of hydrolysis between 87% to 99% and with solid
content in polymer composition between 10% to 50%; and an
amino-formaldehyde oligomer, such as urea-formaldehyde or melamine
formaldehyde with solid content in polymer composition between 50%
to 90%; and optionally including other additives, such as
dispersing agents. An example of the oligomer might be sulfonated
melamine formaldehyde with solid content ranging from 5% to 20%,
with or without a cross-linker.
[0015] In some embodiments, if a cross-linker is needed and used,
it is either a weak acid (boric acid or acetic acid), or a salt
(borax, ammonium chloride and ammonium sulfate) or other weak
aldehydes (such as glyoxal, glutardialdehyde, and others).
[0016] In other embodiments, accelerators and retarders were added
to the polymer composition to control the properties of the
gelants/gels, such as the gelation time, viscosity, gel strength,
and gel stability. Urea=formaldehyde (UF) and sulfonated melamine
formaldehyde (SMF) were synthesized according to procedures
outlined in U.S. Pat. Nos. 4,686,790 and 4,677,159, respectively,
which are hereby incorporated by reference in their entirety.
Example 1
Preparation of Urea-Formaldehyde
[0017] The preparation of urea-formaldehyde (UF) followed a
procedure that was described in U.S. Pat. No. 4,686,790, which is
hereby incorporated by reference in its entirety. Formaldehyde was
heated to 80.degree. C., its pH was raised to 8.5, and then a
solution of water and urea (100 gm H.sub.2O+86 gm Urea) that was
separately prepared was added. The pH of the solution was again set
to 8.5. The mixture was then allowed to react at 80.degree. C. for
30 minutes. After 30 minutes, the pH of the mixture was lowered to
4.8 by adding sulfuric acid, and then allowed to react for another
30 minutes. After 30 minutes, the pH was raised to 7.0, and then
(50-100) gm urea was added. When the urea dissolved completely,
after 5.0 minutes the solution came to equilibrium, and then the pH
of the solution was lowered to 4.8 by adding formic acid. The
mixture is then allowed to cook for 30 minutes. After 30 minutes,
the pH of the solution was raised to 8.0 by adding KOH, and then
allowed to cool to room temperature. The additive, thus prepared,
was filtered and preserved in a bottle after some methanol was
added to cap the reaction. The solid contents ranged between
40-80%, and the viscosities ranged between 500 to 6500 cP when
measured at 20.degree. C. The average molecular weight for the
prepared UF ranged from 4400 to 7350, and the number average
molecular weight ranged from 870 to 930, with polydispersity
ranging from 5.1 to 7.9.
Example 2
Preparation of Sulfonated Melamine Formaldehyde
[0018] The preparation of the sulfonated melamine formaldehyde
(SMF) resins followed a procedure that was developed before in U.S.
Pat. No. 4,677,159, which is hereby incorporated by reference in
its entirety. The preparation procedure follows four steps. In the
first step, a formalin solution of 18% concentration is prepared by
dissolving 50.34 g of 94.6% paraformaldehyde in 230 ml of water.
The reaction mixture is heated at 50.degree. C. for 30 minutes
after its pH is raised by the addition of 0.5 ml of 10 N NaOH.
After the solution becomes clear, 88 ml of water is added to it,
and the solution is heated at 50.degree. C. for an additional 15
minutes. Then, the pH of the solution is raised to 11.35 and 50 g
of melamine is added to it. Upon addition of melamine, it was noted
that the temperature of the reaction mixture increases by about
4-5.degree. C., then falls back gradually to 50.degree. C. within
15 minutes, during which time the melamine dissolves completely by
reacting with formaldehyde. Sodium metabisulfite (37.7 g) and water
(20 ml) are then added to the solution, causing an increase in
temperature of 4-5.degree. C. while the sulfite salt is dissolving.
In the second step, the solution is kept at around 50.degree. C.
for 5 minutes, and then the temperature is raised to 80.degree. C.
in 15 minutes and kept at the new temperature for an additional 45
minutes while maintaining the same pH. In the third step, the
solution is then cooled rapidly (approximately 5 minutes) to
50.degree. C. and 12 ml of 14.5N H.sub.2SO.sub.4 is added to it,
causing a drop in pH to 3.50 and an increase in temperature of
4-5.degree. C. The temperature drops gradually back to 50.degree.
C. within 15 minutes, and the solution is kept under these
conditions with continuous stirring for an additional 95 minutes,
during which it becomes very viscous. The solution is neutralized
afterwards by careful addition of a slurry of calcium oxide (CaO)
in water. The amount of CaO needed is approximately 8.0 g. In the
fourth step, and after neutralization, the solution is heated to
80.degree. C. in about 20 minutes and kept at that temperature for
60 minutes with continuous stirring. The solution is finally
filtered to remove calcium sulfate and other solid particulates,
cooled to room temperature, and treated with sodium hydroxide to
adjust its pH to 9.5.
[0019] The solution prepared according to the above procedure has a
solid content of approximately 23%. The solid content is adjusted
to 20% by addition of water, and the final viscosity of the
solution at 20.degree. C. is 4.20 centipoise (cP). Since the
concentration strongly affects the kinetics of polymerization
reactions, a number of preparations were carried out in which the
concentration of the reactants was increased to values higher than
those mentioned in the standard procedure described above. In these
concentration studies, the procedure used was exactly the same as
that described above for the standard procedure in that the same
masses of melamine, paraformaldehyde, and sodium metabisulfite were
used, but the amount of water added initially during the
preparation of paraformaldehyde was decreased, and the additional
water used in subsequent steps was eliminated completely. SMF
resins were prepared with a final concentration of 43%.
Examples 3-23
Preparation of Various Polymer Compositions
[0020] Various polymeric compositions were then prepared by mixing
different proportions of each using bench top mixers.
Urea-formaldehyde (UF) with sulfonated melamine formaldehyde (SMF)
and other additives was used in single form and in combinations
thereof. The raw materials of urea, melamine, formaldehyde,
sulfuric acid and caustic soda were used in the preparation of new
compositions. Commercial polymers, such as carboxy methyl cellulose
(CMC) and polyvinyl alcohol (PVA), were used. The polyvinyl alcohol
used had molecular weights ranging from 15,000 g/mol to 146,000
ginaol. All of the acids, alcohols and other chemicals that were
used for various compositions were of the technical grade type, and
were obtained off the shelf. Other additives that were used are
described in examples 1 and 2.
[0021] Table 1 shows the physical properties of 21 polymer
compositions that were prepared for evaluation. The rows in Table 1
summarize the 21 samples of the gelling agent, where solutions 1,
2, 3, 10, 11 and 16 are for urea-formaldehyde (UF) and PVA with
different proportions of 60/40, 60/40, 60/40, 70/30, 80/20 and
50/50 UF/PVA, respectively, which also can be distinguished by
their different concentrations. Table 1 shows the main constituents
and their concentrations in the polymer matrix, and the
concentrations and densities of the bulk polymer compositions. The
table also shows the various organic and inorganic cross-linkers
used, along with their weight concentrations in the polymer matrix
and the pH of the final polymer composition solutions. It should be
noted that the concentrations of the cross-linkers are
insignificant as compared to the weight percent of the UF and PVA.
However it should be noted that all the combined weight percentages
all add up to 100%. In summary, the main constituents in the
polymer compositions include urea-formaldehyde and polyvinyl
alcohol with concentrations of the final polymer solutions ranging
from 8.4% to 32.1% after different percentages of different
cross-linkers were added. Other constituents include ethyl acetate,
furfuryl alcohol, butyl acetate, sulfonated naphthalene
formaldehyde, sulfonated melamine formaldehyde, lignosulfonates and
styrene-acrylate copolymer. Different cross-linkers with different
percentages in the polymer compositions include hydrochloric acid
(0.412%-1.5%), boric acid (0.0125%-0.1%), borax (0.015%-0.1%) and
acetic acid (0.11%-10%). The percentages of the cross-linkers are
by weight of the polymers in the compositions. The pH of the
resulting compositions depends on the type and amount of the
cross-linkers used, where they range from 0.25-2.21 in the case of
HCl, to 5.6-9.9 in the case of Borax.
TABLE-US-00001 TABLE 1 Physical Properties of some of the Polymer
Compositions Prepared for Water Shut-off in Oil and Gas Wells
Cross-linkers Example Component/ (% wt. of Concentration No.
Composition Composition) pH (g/cc) 1 UF + PVA No Acid 5.6 23.00
(60/40) HCl (0.412-1.24) 1.89-1.3 Boric (0.0125-0.1) 5.6-5.3 Borax
(0.0125-0.1) 5.6-7.0 Acetic (0.025-0.4) 5.0-4.1 2 UF + PVA HCl
(0.412-1.24) 2.21-1.2 12.83 (60/40) Boric (0.025-0.1) 5.6-5.4 Borax
(0.025-0.1) 5.6-6.12 Acetic acid (1-10) 4.0-3.21 3 UF + PVA HCl
(0.412-1.24) 2.2-1.2 8.40 (60/40) Boric (0.025-0.1) 5.7-5.6 Borax
(0.025-0.1) 6.5-6.45 Acetic acid (1-10) 3.9-3.3 4 UF + FA + HCl
(0.33-1.5) 1.1-0.25 43.00 PVA + EAC S.A. (0.5-1.0-1.5) 4.0-1.63 5
FA + EAC S.A. (0.5-1.0) 1.1-0.5 34.30 6 UF + PVA + SMF Acetic acid
(0.11-0.44) 5.7-5.0 22.49 7 UF + PVA + SMF Acetic acid (0.11-0.44)
5.7-5.25 24.34 8 3 + 4 Acetic acid (0.25-1.0) 4.7-4.15 16.28 9 3 +
5 Acetic acid (0.25-1.0) 4.7-4.16 14.69 10 UF + PVA Boric
(0.025-0.1) 5.9-5.85 25.18 (70/30) Borax (0.025-0.1) 6.2-7.2 Acetic
(0.11-0.44) 5.2-4.2 11 UF + PVA No Acid 5.6 32.10 (80/20) Boric
(0.025-0.1) 6.1-5.4 Borax (0.025-0.1) 6.4-7.46 Acetic (0.11-0.44)
5.2-4.2 12 UF + PVA + SNF No Acid 6.11 22.68 Acetic (0.11-0.44)
5.2-4.2 13 UF + PVA + SNF No Acid 6.31 25.13 Acetic (0.11, 0.22,
0.44) 5.8-4.9 14 UF + PVA + SL No Acid 6.90 21.50 Acetic
(0.11-0.44) 6.2-4.9 15 UF + PVA + SL No Acid 7.04 23.20 Acetic
(0.11-0.44) 6.8-5.3 16 UF + PVA No Acid 5.26 17.58 (50/50) 17 UF +
PVA + SF* No Acid 5.11 19.99 18 UF + PVA + SF* No Acid 5.38 23.45
19 UF + SF No Acid 5.19 29.40 20 UF + PVA + SF No Acid 5.19 29.00
Boric (0.22) 5.2 Borax (0.22) 5.97 Butyl Acetate(0.22) 5.14 Acetic
(0.22) 21 UF + PVA + EAC No Acid 4.58 17.64 Acetic (0.22) 2.72 *UF:
Urea Formaldehyde PVA: Polyvinyl Alcohol EAC: Ethyl Acetate F.A:
Furfurly Alcohol S.A: Toluene-4-P-Sulfonic Acid A.A: Acetic Acid
B.A: Butyl Acetate SNF: Sulfonated Naphthalene Formaldehyde SL:
Lignosulfonates SF: Styrene-Acrylate co-polymer SMF: Sulfonated
Melamine Formaldehyde
[0022] Table 2 is a summary of the main characteristics of the 21
polymer compositions that were developed and reported in Table 1.
The pertinent characteristics include the polymer composition
concentration, the 100% gelation time at various temperatures
ranging from 60.degree. C. to 120.degree. C., the elastic nature of
the formed gel and its stability at the test temperature, as well
as after it has been aged at 90.degree. C. for extended periods of
time exceeding 1018 hrs. The 100% gel time for the various
compositions range from about one hour at 80.degree. C. to about 33
hours at 60.degree. C., and some of these compositions never formed
a gel (even after being aged for more than 200 hrs. at 80.degree.
C.) in the absence of cross-linkers. The gels that were formed at
the temperatures shown were aged at 90.degree. C. for extended
periods of time exceeding 1000 hours to check their degree of
stability. Two main parameters were observed, namely, the gel type,
and the syneresis and shrinkage and production of water as
expressed in percent of water production. It was found that for all
the 21 polymer compositions that were prepared and tested, no
syneresis (spontaneous separation of a liquid from a gel due to
contraction of the gel) took place, even after they have been aged
at 90.degree. C. for more than 1018 hours. This might be due to the
absence of cross-linkers in some of the compositions. Another
observation is that the various gels that were formed maintained
their elastic nature for a certain period of time when aged at
90.degree. C., but changed to viscous gels and lost their elastic
nature after that aging time. However, the elastic nature of some
formed gels can be prolonged for extended periods of time if
certain additives are added to these polymer compositions. These
additives include some dispersants, such as sulfonated naphthalene
formaldehyde and sulfonated melamine formaldehyde. On the other
hand, some of these dispersants can accelerate the loss of
elasticity, and these include lignosulfonates. Gel elasticity was
also measured, and a rating was given to various formulations
ranging from zero to ten, where zero (0) refers to liquid-like and
ten (10) refers to strong elastic gel. Gel elasticity for the
various gels that are reported in Table 2 ranged from 5 to 8.
TABLE-US-00002 TABLE 2 Physical Properties of Polymer Compositions
Gel Stability aged at 90.degree. C. Gel type at Polymer Conc. 100%
Gelation Time (hrs.)* Gel Elasticity* various aging % -water No.
composition (%) 60.degree. C. 80.degree. C. 90.degree. C.
110.degree. C. 60.degree. C. 80.degree. C. 90.degree. C.
110.degree. C. time (hrs.) Produced 1 (UF + PVA) 23 33 9.75 6 2.00
5 5 5 5 elastic < 858 < 0 60/40 viscous fluid 2 (UF + PVA)
12.83 No Gel No Gel No Gel No Gel N/A N/A N/A N/A N/A 0 60/40 3 (UF
+ PVA) 7.65 No Gel No Gel No Ge No Gel N/A N/A N/A N/A N/A 0 60/ 4
(UF + FA + 43 No Gel No Gel No Gel No Gel N/A N/A N/A N/A N/A 0 PVA
+ EAC) 5 (FA + EAC) 34.3 No Gel No Gel No Gel No Gel N/A N/A N/A
N/A N/A 0 6 (UF + PVA + SMF) 22.5 25 6.5 3.75 1.25 6 6* 7* 7.00
elastic > 528 0 7 (UF + PVA + SMF) 24.34 22 5 2.75 1.00 6 6 7
7.00 elastic > 525 0 8 (UF + PVA) 16.28 N/A No Gel No Gel No Gel
N/A N/A N/A N/A N/A 0 9 (UF + PVA) 14.69 N/A No Gel No Gel No Gel
N/A N/A N/A N/A N/A 0 10 (UF + PVA) 25.18 28.5 8 4 1.50 6 6 6 6.00
elastic < 888 < 0 70/30 viscous gel 11 (UF + PVA) 32.1 26 7 3
1.25 6 6 6 6.00 elastic < 984 < 80/20 viscous gel 12 (UF +
PVA + SNF 22.68 14 10 8.5 3.00 N/A 6 8 8.00 elastic < 1018 <
elastic 13 (UF + PVA + SNF) 25.13 16 12.5 10.5 3.50 N/A 6 8 8.00
elastic < 1018 < elastic 14 (UF + PVA + SL) 20.5 39 17 14 No
Gel N/A 5 5 N/A soft elastic < 0 792 < viscous fluid 15 (UF +
PVA + SL) 23.2 50 27 25 No Gel N/A 5 5 N/A soft elastic < 0 792
< viscous fluid 16 (UF + PVA) 17.58 50 24.50 21.00 No Gel N/A 4
4 N/A elastic > 525 0 17 (UF + PVA + SF'') 20.0 22 8.50 7.00 No
Gel 5 5 7 N/A elastic > 525 0 18 (UF + PVA + SF) 23.45 12 4.50
3.25 1.50 6 8.00 8.00 5.00 elastic > 525 0 19 (UF + SF'') 29.4
N/A No Gel No Gel No Gel N/A N/A N/A N/A N/A 0 20 (UF + PVA + SF)
29 9 2.25 1.75 1.00 7 8.00 8.00 5.00 elastic > 525 0 21 (UF +
PVA + EAC) 18.96 44 14.00 10.00 No Gel 5 5 5 N/A elastic 0 *Gel
elasticity grading: rating from 0 to 10 where 0 is liquid form and
10 is very strong elastic gel. 4: soft elastic gel 5: Medium soft
elastic gel 6: Elastic gel 7: medium elastic gel 8: strong elastic
gel
[0023] The effect of several variables on the characteristics and
behavior of the newly developed polymer gels (both concentrated and
diluted) was fully investigated and are reported in this patent
disclosure. These variables include: the cross-linkers type and
concentration, the concentration of the polymer compositions, brine
(3% KCl), dispersants and other additives, shear rates, pressure
imposed, and thermal aging of some polymer compositions with
different percentages of brine.
Example 24
Effect of Cross-Linkers on the Gel Properties of Concentrated
Polymers
[0024] The effect of cross-linker type and its concentration on
gelling behavior of the concentrated polymer compositions was
evaluated. Tables 3 and 4 are a summary of the 100% gelation time
for polymer composition number 3, where the solution concentration
is about 23%, with different cross-linkers tested at different test
temperatures. The type of gel and the percent of water produced
upon aging at 90.degree. C. as syneresis are also shown. The
results show that the main parameters that control the gelling
behavior are the concentration of the polymer composition, the type
of cross-linker and its concentration, the temperature of testing
and the type and the constituents of the polymer composition used.
When hydrochloric acid (HCl) is used as a cross-linker, initial gel
formation took place in the first half hour, and complete gelation
took place in about 7.25 hours for all the HCl concentrations used,
which range between about 0.4% to about 1.2% at 60.degree. C.
However, HCl tends to produce gels that produce water upon
prolonged exposure at 60.degree. C. Boric acid with concentrations
ranging from 0.0125% to 0.25% produced complete gels in about 33
hrs at 60.degree. C. for solution No. 3. Similarly, Borax with
concentrations ranging from about 0.0125% to 0.25% gave 100% gel in
about 33 hours to 45 hours at 60.degree. C. This shows that Borax
is slower in producing the gels than Boric acid. On the other hand,
organic cross-linker Acetic Acid with concentrations ranging from
0.0125% to 0.66% by weight of the polymer gave 100% gel in 28 hours
to 3.5 hours respectively when tested at 60.degree. C. It was found
that Boric acid and Borax delay gelation time, while acetic acid
tends to accelerate gelation. It was also found that upon aging at
80.degree. C., all the gels cross-linked with Boric acid and Borax
remained elastic, while those cross-linked with acetic acid remain
elastic up to more than 1000 hours, and transformed into spongy
gels after that, with the production of some water. The production
of water is due to syneresis of these gels when they are
cross-linked with higher doses of acetic acid. Also, as the
concentration of acetic acid increases, the gel elasticity
decreases with aging time. Ammonium chloride (NH.sub.4Cl) and
ammonium sulfate (NH.sub.4).sub.2SO.sub.4 produce gels that are
spongy, but significant syneresis took place upon storage at
90.degree. C. For example, while gelation time is almost instant
with polymer solution number 3 (.about.0.25 hour gelation time),
40% of water was produced as a result of syneresis of the formed
gel with these two cross-linkers. The results also show that as
temperature increases, the gelation time decreases. Gelation times
of some concentrated and diluted polymer compositions with acetic
acid at room temperature are shown in Table 3.
[0025] Table 3 shows that composition No. 3 has a gelation time at
ambient temperature ranging from 8 hours when 10% acetic acid is
added to 1920 hours without the addition of acetic acid. Similar
trends are also shown for other diluted and concentrated polymer
compositions.
[0026] The effect of other cross-linkers, such as NH.sub.4Cl,
(NH.sub.4).sub.2SO.sub.4, glyoxal, and glutardialdehyde on the
gelation time of composition No. 1 is also shown in Table 4.
Gelation time is very fast for both (NH.sub.4).sub.2SO.sub.4 and
NH.sub.4Cl (about 0.25 hours when tested at 60.degree. C. and
80.degree. C.). However, the gels went through syneresis and
produced water after only 48 hours of aging at 90.degree. C. On the
other hand, Glyoxal and Glutardialdehyde are very slow
cross-linkers, where gelation took place after 32 hours at
60.degree. C., which is practically the same gelation time for
polymer composition number 1 without cross-linkers.
TABLE-US-00003 TABLE 3 Gelation Time for Various Compositions
Polymer Concentration Acetic Acid Gelation Time Composition (%) (%)
(Hrs.) 1 23.00 0.00 1920 1 23.00 2.00 35 1 23.00 3.00 27 1 23.00
4.00 24 1 23.00 5.00 20 1 23.00 10.00 '8 1 + 0.11% AA 23.00 0.11
349 11C + 0.11% AA 24.30 0.11 612 12D + 0.11% AA 20.18 0.11 225
11C-1 + 3% AA 18.00 3.00 126 12D-1 + 3% AA 18.00 3.00 56 1-1 + 3%
AA 18.00 3.00 75 11C-1 + 3% AA 18.00 1.00 228 12D-1 + 1% AA 18.00
1.00 79 1-1 + 1% AA 18.00 1.00 115
TABLE-US-00004 TABLE 4 Gelation Time and Stability of Polymer
Composition 1 With Various Cross-Linkers Cross- Gel Stability aged
at 90.degree. C. linker 100% Gelation Time (hrs.) Gel type at
various Cross-Linker Wt % 60.degree. C. 80.degree. C. 90.degree. C.
110.degree. C. aging time (hrs) H.sub.2O % None 0 33.00 9.75 6.00
2.00 elastic < 858 < viscous 0 HCl 0.412 7.25 N/A N/A N/A
Spongy > 766 hrs 36 0.825 7.25 N/A N/A N/A Spongy > 766 hrs
52 1.24 7.25 N/A N/A N/A Spongy > 766 hrs 56 Boric Acid 0.0125
33.00 9.75 6.00 N/A elastic < 858 < viscous 0 0.025 33.00
9.75 6.00 N/A elastic < 858 < viscous 0 0.05 33.00 9.75 6.00
N/A elastic < 858 < viscous 0 0.1 34.00.sup.1 9.75 6.00 N/A
elastic < 858 < viscous 0 0.25 35.00 11.75 7.00 2.50 elastic
< 858 < viscous 0 Borax 0.0125 33.00 9.75 6.00 N/A elastic
< 858 < viscous 0 0.025 33.00 10.75 6.00 N/A elastic < 858
< viscous 0 0.05 34.00 10.7 6.00 N/A elastic < 858 <
viscous 0 0.1 34.00 12.75 7.00 N/A elastic < 858 < viscous 0
0.25 45.00 23.00 19.50 11.00 elastic < 858 < viscous 0 Acetic
Acid 0.0125 28.00 8.00 4.00 1.75 elastic < 858 < viscous 0
0.025 22.00 7.00 4.00 1.50 elastic < 858 < viscous 0 0.05
18.00 3.75 3.25 1.25 elastic < 858 < viscous 0 0.11 10.00
2.00 1.00 0.50 elastic < 642 < spongy 18 0.22 7.00 1.50 0.50
0.35 elastic < 642 < spongy 18 0.44 5.00 1.25 0.50 0.25
elastic < 426 < spongy 18 0.66 3.50 1.00 0.50 0.25 elastic
< 282 < spongy 18 NH.sub.4Cl 1 0.25 0.25 N/A N/A spongy, 1344
hrs 40** 2 0.25 0.25 N/A N/A spongy, 1344 hrs 40**
(NH.sub.4).sub.2SO.sub.4 0.5 0.50 0.50 N/A N/A spongy, 1344 hrs
40** 1 0.25 0.25 N/A N/A spongy, 1344 hrs 40** Glyoxal 0.5 32.50
9.00 N/A N/A Elastic, 1128 hrs 0 1 32.00 8.00 N/A N/A Elastic, 1128
hrs 0 Glutardialdehyde 0.5 32.50 8.75 N/A N/A Elastic, 1128 hrs 0 1
32.00 7.50 N/A N/A Elastic, 1128 hrs 0 *Gels were aged at
80.degree. C. for 766 hrs **Gels were aged at 90.degree. C. and
syneresis after only 48 hrs
Example 26
Effect of Cross-Linkers on Gel Properties of Diluted Polymers
[0027] The effect of some cross-linkers on the gelation time, gel
strength and gel stability of diluted polymer compositions was also
evaluated. Ammonium chloride (NH.sub.4CI) and Ammonium sulfate
(NH.sub.4).sub.2SO.sub.4 produce gels that are spongy, but
significant syneresis takes place upon storage at 90.degree. C. For
example, while gelation time is almost instant with polymer
solution No. 1 (-0.25 hour-gelation time), 40% of water was
produced as a result of syneresis of the formed gel with these two
cross-linkers, as was shown in Table 4. The same trend was observed
when these two cross-linkers were used with polymer solutions Nos.
1-3, 8 and 9, where the water produced upon syneresis was about
80%, 36% and 44%, respectively. Acetic acid, on the other hand,
shows to be a very good cross-linking agent for our polymer
solutions, and no syneresis took place, even after storing the
formed gels at 90.degree. C. for more than 1300 hrs. Also, glyoxal
and glutardialdehyde produce good elastic gels when they are used
as cross-linkers with polymer solution Nos. 1 and 12. No syneresis
was observed when they are used with polymer solution No. 1 even
after aging of gels for more than 1120 hours at 90.degree. C.
However, 20% of water was produced when these two cross-linkers
were used with polymer solution No. 12, indicating that syneresis
took place after storing the gel at 90.degree. C. for more than
1440 hrs. The gels that were formed from polymer solution No. 1
were elastic, while those formed from solution No. 12 were spongy,
and this might be attributed to the syneresis of the latter upon
storage or aging at 90.degree. C. Finally, it was noted that acetic
acid is more effective as a cross-linker than glyoxal or
glutardialdehyde because far smaller amounts of acetic acid are
used to gel the polymer solution for the same period of time. For
example, for 1% of glyoxal or glutardialdehyde by weight of polymer
solution No. 1, the gelation time is about 32 hrs. at 60.degree.
C., compared to a gelation time of only about 28 hours when 0.0125%
of acetic acid (AA) is used. Therefore, acetic acid is more
economical to use and produces gels that are more elastic and more
stable when aged at 90.degree. C. for extended periods of time, and
without any syneresis. The gel strength and gel elasticity for some
polymer compositions were graded qualitatively from 1 to 10, where
10 is a very strong and elastic gel when it is poked with a rod or
solid object, and number 1 is for very soft and flowing gel.
Polymer composition No. 1 gave an intermediate strong gel, where it
is very elastic and somewhat soft, and was given a grade of 5-6 for
all temperatures ranging from 60.degree. C. to 90.degree. C.
Polymer composition No. 11 gave a little more stronger gel and was
given a grade of 6-7, while polymer composition No. 11C, which is
the same as polymer composition No. 11 except that it is more
diluted, was much softer and was given a grade of 3-4, depending
upon the degree of cross-linking. It was found that the percentage
of cross-linking agent increases the grading of the gel formed, and
this is evident in polymer compositions No. 11C and No. 12D. For
example, polymer composition No. 11C with 0.05% and 0.11% acetic
acid as a cross-linker gave gel grades of 3 and 4, respectively.
Similarly, polymer composition No. 12D with 0.0%, 0.05%, 0.11% and
0.22% acetic acid as a cross-linker gave a gel strength grade of 5,
6, 7, and 8, respectively. The strongest gel was formed by polymer
composition No. 12, where a gel strength grade of 8 was given when
they were formed at 80.degree. C. and 90.degree. C. The use of some
dispersants with the polymer composition gives rise to the gel
elasticity. The effect of pressure is evident on polymer solution
12D-1 where gelation took place after 72 hours at 80.degree. C.
with no cross-linkers.
Example 27
Effect of Polymer Composition Concentration on their Gel
Properties
[0028] The effect of concentration of polymer compositions on
gelation behavior was studied. Table 5 shows the effect of polymer
concentration on the 100% gelation time of polymer composition No.
1 at different temperatures and for different additives, such as
ethyl acetate and acetic acid. Table 5 shows that polymer solution
No. 1 concentrations ranging from 7.65% to 23% do not form gels at
all temperatures, even after they have been exposed to about 200
hours with acetic acid as a cross-linker. However, the effect of
Urea-Formaldehyde (UF) and Polyvinyl alcohol (PVA) concentrations
in the main polymer composition matrix has opposite effects. The
higher the UF concentration, the faster the composition will gel,
and the higher the PVA concentration in the composition, the higher
is the 100% gel time for these compositions. Again, syneresis took
place when gels that were formed by using such cross-linkers as
ammonium sulfate and ammonium chloride after storing at -90.degree.
C. Finally, the addition of ethyl acetate (EAC) to the polymer
matrix delays gelation from 33 hours to 44 hours when tested for
the concentrated polymer composition No. 1 at 60.degree. C., and no
gel was formed at higher temperatures of 80.degree. C., 90.degree.
C., and 110.degree. C.
TABLE-US-00005 TABLE 5 Gelation Time as Affected by Polymer
Concentration Cross- Cross- Polymer Polymer Linker Linker 100%
Gelation Time (hrs) Comp. Conc. % Type % 60.degree. C. 80.degree.
C. 90.degree. C. 110.degree. C. H.sub.2O % 1 23.00 N/A 0 33 9.75 6
2 0 1-1 18.00 AA 1 60 29 0 2 50 25 0 3 46 22 0 1-2 14.00 AA 2 73
32% 0 (NH.sub.4).sub.2SO.sub.4 1 5 65 1-3 7.65 NH.sub.4Cl 1 17 4.75
80 2 12 3.5 80 (NH.sub.4).sub.2SO.sub.4 0.5 42 17.5 80 1 30 12 80 8
16.28 NH.sub.4Cl 0.5 6.5 2 36 1 4.5 1.5 36 (NH.sub.4).sub.2SO.sub.4
0.5 23 4 36 1 12 12 36 9 14.69 NH.sub.4Cl 0.5 1 1 44 1 1 1 44
(NH.sub.4).sub.2SO.sub.4 0.5 2 1.5 44 1 1 1 44 1 + EAC* 17.64 N/A 0
44 No No No N/A Gel Gel Gel 1 + EAC ++ AA** 17.41 AA 0.22 12 No No
No N/A Gel Gel Gel *EAC: Ethyl Acetate, prepared in brine (3% KCl)
**AA: Acetic Acid ***Aging @ 90.degree. C.
Example 28
Effect of Brine on the Properties of Some Polymer Gels
[0029] The effect of brine (3% KCl) percentage in the polymer
compositions on the polymer gels behavior was investigated. The
effect of brine (3% KCl) on the 100% gelation time of polymer
composition No. 1 was found to be significant. Data shows that as
the brine concentration increases, the 100% gelation time gets
delayed quite significantly. For example, increasing the
concentration of brine in the polymer matrix from 0% to 20% delays
the gelation time from 6 hours to 30 hours when tested at
90.degree. C. However, in the presence of a cross-linker, such as
acetic acid with polymer composition No. 1, the effect of brine on
the delay of gelation time gets dampened. The same trend was also
observed for solutions nos. 11, 11C and 12D. However, it was found
that this behavior is due to the dilution effect that the brine has
when it is mixed with the various polymer compositions. Therefore,
the delay in gel time is due to dilution of the polymer
compositions by brine.
Example 29
Effect of Shear Rate on the Properties of Some Polymer
Compositions
[0030] The effect of shear rate on the viscosity and gelation time
of concentrated and diluted polymer compositions upon thermal aging
at 80.degree. C. was investigated. The viscosities were measured
using a Haake rotational viscometer at a shear rate of 100
s.sup.-1. The samples were placed in the viscometer for different
periods of time, and they were sheared as time elapsed. The data
shows the effect of aging at 80.degree. C., plus the effect of
shear rates on the viscosity build-up. It is noticed that shear
accelerates cross-linking quite drastically. For example, solution
No. 11 appears to approach gelation at about 4-5 hours at a shear
rate of 100 s.sup.-1, while the established gelation time for this
solution at zero shear rate is 7.0 hours at 80.degree. C. Similar
behavior has been observed for other solutions. For example,
polymer solutions no. 12D and no. 1 appear to have gelation times
of 8-9 hours under shear of 100 s.sup.-1, compared to 15 and 9.75
hours at zero shear rates, respectively, when measured at
80.degree. C. Therefore, it can be concluded that shear accelerates
gelation times of these polymeric solutions.
[0031] The results also show that viscosity build-up increases as
the shear rate increases. Furthermore, as the viscosity build-up
increases, the gelation time to obtain 100% gelation decreases.
This is expected, since shearing the polymer solutions makes the
molecules come closer to each other and because of the presence of
a cross-linker that accelerates gelation, which tends to increase
the viscosity. It should be noted that there are two competing
mechanisms that work opposite to each other. One mechanism is that
shear rates, for non-cross-linking, non-Newtonian systems, tend to
lower the viscosity of the systems. On the other hand, the second
mechanism is that for cross-linking and non-Newtonian systems, the
viscosity buildup increases with shear due to the closeness of the
molecules to each other upon shearing. In both cases, the
concentration of the compositions and the concentration of the
cross-linker play a significant role. The viscosity builds up, and
hence gelation time is accelerated for concentrated solutions. The
absence of a cross-linker in polymer solution No. 1 made the
solution behave as a non-Newtonian system, where viscosity
decreases as shear rate increases. However, polymer solutions No.
11C and 12D, with a cross-linker of acetic acid, behave as dilatant
fluids, where the viscosity increases upon high shear. Again, the
mechanism of cross-linking upon high shear tends to induce higher
viscosities because the cross-linked chains experience elongation
flow, and hence, higher viscosity. It is well known that the
elastic modulus of polymers experiencing elongation flow is three
times that of the shear modulus, and hence, the elongation
viscosity is expected to be about three times the viscosity under
shear.
[0032] Again, as expected, the higher the cross-linker
concentration is, the higher the viscosity. However, for dilute
polymer solutions, such as Nos. 1-2+2% AA, where the concentration
is about 16%, the viscosity at a shear rate of 100 s.sup.-1 gave
slightly higher viscosity than a 200 s.sup.-1 shear rate,
indicating that less shear is preferred to induce cross-linking.
But in all cases, viscosity increases upon shearing and thermal
aging.
Example 30
Effect of Pressure on the Gelation Time of Some Polymer
Compositions
[0033] The effect of pressure on the gelation time of some polymer
compositions was investigated and the results are shown in Tables 6
and 7. Polymer solution no. 1 has a gelation time of 9.75 hours
when it was stored at 80.degree. C. and under an atmospheric
pressure of 14.7 psi, compared to 3.5 hours of gelation time after
it had been stored at 80.degree. C. under 1000 psi pressure.
Similar trends are noted for other concentrated polymer solutions,
including Nos. 11, 11C, 12, and 12D, which all exhibit accelerated
gelation time under pressure, both with and without a cross-linker.
Therefore, it can be concluded that the polymer solutions reported
here would gel much faster when they are sheared and stored at
higher pressures that resemble reservoir conditions, than those
polymer compositions that are stored at atmospheric pressure under
static conditions. The data in Table 6 shows that the gelation time
was accelerated as the pressure increases, signaling more
cross-linking, and hence faster gelation for concentrated polymer
solutions. Table 7 shows the effect of pressure on gelation time of
diluted polymer compositions prepared in brine. Again, the effect
of pressure in inducing gelation is not significant in the presence
of brine.
TABLE-US-00006 TABLE 6 Effect of Pressure on the Gelation Time of
Concentrated Polymer Compositions Stored at 80.degree. C. and 1000
psi Cross-Linker Polymer Concentration (Acetic Acid) Gelation Time
(hrs) Solution (%) (Wt. %) At 1000 psi At 14.7 psi 1 23 0 3.5 9.75
11 32.1 0 2.5 7.00 12 22.68 0 3.0 10.00 12D 20.18 0 6.5 15.00 0.11
4.0 4.50 11C 24.07 0 6.5 18.50 0.11 3.0 4.75
TABLE-US-00007 TABLE 7 Effect of Pressure on the Gelation Time of
Diluted Polymer Compositions Prepared in 3% KCl Brine and Stored at
80.degree. C. and 1000 psi Polymer Cross-Linker Polymer Conc.
(Acetic Acid) % Gelation Stored for 24 hrs. Comp. (%) (Wt. %) at
1000 psi at 14.7 psi 1-2 11.95 2 (3 5% gel) (25% gel) 11C-2 13.01 2
(35% gel) (25% gel) 12D-2 11.35 2 (35% gel) (25% gel)
Example 31
Effect of Brine on the Rheology and Gelation Time of Some Polymer
Compositions
[0034] The effect of brine (3% KCl) on the rheology and gelation
time of some polymer compositions was evaluated. The viscosities of
various polymer solutions are measured with different brine (3%
KCl) concentrations upon aging at 80.degree. C. using the Haake
rotational viscometer at a shear rate of 100s.sup.-1. Table 8 shows
the viscosities and gelation times of various polymer solutions
with and without brine upon aging at 80.degree. C. Brine
concentrations ranging from 0.0% to 15% by weight of polymer
solutions were added to various polymer compositions to see their
effect on the gelation time and on the viscosity of the
compositions. Table 8 shows that as the concentrations of brine
increases from 0.0% to 15% in the polymer compositions, gelation
time gets delayed by a factor of two to ten, and even more in some
cases. Similarly, the viscosity of various polymer compositions
drops by a factor of two when the brine concentration increases
from 0.0% to 15.degree. A. The effect of brine accompanied with
shear rate and aging time is shown in the table. In all cases, an
increase of brine reduces the viscosity and increases the gelation
time for all of the polymer compositions that were tested. The data
shows that about 50% viscosity reduction could take place for brine
concentrations ranging from 0.0% to 15% by weight of the polymer
solution. Again, the reduction in viscosity and increase in
gelation time are due to the dilution of the polymer compositions
by the inclusion of brine.
[0035] Table 8 also shows the effect of brine on viscosity
reduction of various diluted polymer compositions. Viscosity
reduction was minimal for diluted compositions of about 6%
concentration when the brine concentration changed from 0% to 15%.
On the other hand, viscosity dropped by about a factor of 1.5 for
intermediate polymer concentrations (i.e., 12%) for brine
concentrations ranging from 0.0% to 15%. Again the drop in
viscosity is due to the dilution effect by the brine. The effect of
polymer composition concentration on the viscosity is very
significant, as can be seen from Table 8.
TABLE-US-00008 TABLE 8 100% Gelation Time and Viscosities of
Different Polymer Compositions at different Brine Concentrations
upon Aging at 80.degree. C. Polymer 100% Gelation Time (hrs.) at
80.degree. C. for Viscosity at 80.degree. C. and 100 s.sup.-1 for
different Polymer Concen. different brine % in polymer brine %,
(cP) Composition (wt %) 0% 5% 10% 15% 0% 5% 10% 15% 1 23.00 9.75 13
16.5 26.0 94.00 90.10 72.80 59.40 1-1 + 3% AA 18.00 22.00 -- -- --
80.00 75.00 52.04 44.05 1-2 + 2% AA 10.72 24 (25%) -- -- -- 10.30
9.20 7.90 7.30 1-3 + 2% AA 6.02 24 (20%) -- -- -- 4.10 4.10 4.00
4.10 11 32.10 7.00 10.0 -- 17.00 117.50 80.60 67.30 58.40 11C 24.07
18.50 62 62 (60%) 62 (60%) 31.70 24.80 21.40 19.70 11C + 0.11% AA
24.07 4.75 6.5 48 (60%)+ 62 (60%) 68.00 39.20 27.20 22.90 11C-1 +
3% AA 17.65 25.00 -- -- -- 17.20 16.14 14.00 13.00 11C-2 + 2% AA
10.65 24 (25%) -- -- -- 4.50 4.60 4.70 4.40 11C-3 + 2% AA 6.32 24
(20%) -- -- -- 4.70 3.90 3.40 3.50 12 22.68 10.00 62 72 72 418.50
261.90 186.70 149.70 12D 20.18 15.00 62 62 62 125.90 107.40 82.60
71.00 12D + 0.11% AA 20.18 4.50 <89 <89 <89 667.4* 260.0*
218.6* 178.7* 12D-1 + 3% AA 18.00 22.00 -- -- -- 404.00 150.00
125.00 94.00 12D-2 + 2% AA 9.25 24 (25%) -- -- .sup. --' 9.40 8.40
7.20 6.60 12D-3 + 2% AA 6.25 24 (25%) -- -- -- 4.90 4.50 4.10 4.00
62 47.00 2.50 10 48 (32%) -- -- -- -- -- (SF + SNF) 62(2) 51.51 48
.(20%) 62 (8%) 62 (8%) 62 (8%) 14.13 -- -- -- (SF + SNF)
Viscosities of solution 12D + 0.11% AA were measured at 60.degree.
C.
Example 32
Effect of Cross-Linkers and Concentration on Some Polymer Gel
Stability
[0036] The effect of cross-linker type and concentration on the gel
stability of various polymer compositions was evaluated. The
stability of the gels formed by the polymer compositions is a very
important property that needs to be achieved. Gel stability is
defined here as being a gel that remains elastic and durable,
doesn't synerese or produce water, and maintains its original
quality and integrity and strength when it is exposed to elevated
temperatures. The gels that were produced and discussed above were
exposed to further ageing at 80.degree. C. in an air circulating
oven. The above characteristics of the gels were observed and
recorded as a function of time. The results show that for polymer
composition No. 1, all the 100% gels that were produced by
cross-linkers of Boric acid and Borax were stable, even after 858
hours of exposure at 90.degree. C. for all the ranges of
concentrations studied. Similar behavior was also observed for
acetic acid with the concentrations between 0.11% to about 0.66%.
However, for concentrations of acetic acid equal to or exceeding
1%, about 10% of water is being produced after 672 hours of
exposure at 90.degree. C. For higher concentrations of acetic acid,
the production of water increases. Therefore, concentrations of
0.5% or less of acetic acid would give a stable gel with solution
No. 1. For polymer compositions No. 2 and No. 3, no stable gels can
be maintained at 80.degree. C. for any of the cross-linkers tested.
Solution No. 3 has no gel formation, and therefore the study of
stability does not apply. As for polymer composition No. 4, the
gels formed by both HCl and Sulfonic acid were stable at 80.degree.
C., even after exposure of about 766 hours in the case of HC 1, and
about 514 hours in the case of sulfonic acid. However, both
cross-linkers produce brittle gels. Finally, polymer composition
No. 5 produces hard, black gels with sulfonic acid cross-linker,
and is very stable after exposure at 80.degree. C. for 514 hrs.
Example 33
Effect of Brine on Gel Stability and Strength of Some Polymer
Compositions
[0037] The effect of brine on the gel stability and strength of
various polymer compositions was studied. Tables 9 and 10 show the
gel stability and gel strength of three main polymer gels that were
prepared in tab water, and in tab water with brine placed on top.
All of these gel systems were stored at 80.degree. C. The gels that
were prepared in tab water were most stable and didn't synerese,
even after they had been aged for about 858 hours at 80.degree. C.
They also maintained their strength with no appreciable change.
However, when brine was placed on top of these gels, they lost
imbedded water of about 40% after 768 hours of aging at 80.degree.
C. for composition No. 1, No. 11C+0.11% A.A. and 12D+0.11% A.A., as
shown in Table 9. On the other hand, for the gels that were
prepared in 100% brine (3% KCl), as shown in Table 10, the gel
strength is reduced quit significantly compared to the gels
prepared in tab water, as shown in Table 9. The gels that were
prepared in tab water with brine replaced on top showed some
reduction in strength, but not as significant as it was with gels
that were prepared in 100% brine. Another observation is that in
the presence of brine, whether it is imbedded as a whole in the
gels or is brine that is placed on top, some syneresis took place.
However, syneresis was more pronounced in the case of gels prepared
in 100% brine.
TABLE-US-00009 TABLE 9 Gel Stability and Gel Strength of
Concentrated Polymer Compositions Prepared in Tab Water and aged at
80.degree. C. Gel Prepared in Tab Gel Prepared in 100% Water and
Stored Gelation Tab Water Only With Brine on Top* Time Stability
Stability Polymer (hrs) @ H.sub.2O Gel H.sub.2O Gel Comp.
80.degree. C. Hrs (%) Strength** Hrs (%) Strength.sup.$ 1 9.75 858
0 6 768 40 Spongy 11C + 0.11% A.A. 4.75 858 0 5 768 40 Spongy 12D +
0.11% A.A. 4.50 858 0 7 768 40 Spongy *The 3% KCl Brine was added
on top of the polymer gels **Gel strength grading is qualitative
and it was given numbers from 0-{grave over ( )}0, where 0 is
water-like and {grave over ( )}0 means very strong and elastic gel
.sup.$Spongy gels are those gels that lose water upon syneresis
TABLE-US-00010 TABLE 10 Gel Stability and Gel Strength of
Concentrated Polymer Compositions Prepared in 100% (3% KC1) Brine
Upon Aging at 80.degree. C. Gel Prepared in Brine and Stored at
80.degree. C. With Brine Gel Prepared in 100% Brine on Top
Stability Stability Polymer H.sub.2O Gel H.sub.2O Gel Comp. Hrs (%)
Strength Hrs (%) Strength 1 672 20 4 504 40 4 11C + 672 52 2 504 55
4 0.11% A.A. 12D + 672 50 3 504 60 4 0.11% A.A.
[0038] The case where polymer gels are prepared in 100% tab water
and aged at a temperature of 80.degree. C. with brine (3% KCl)
placed on top represents the real case of water shutoff or sand
consolidation treatment with these gels. The polymer compositions
prepared in 100% tab water will be injected first in the producing
oil and/or water formation. These polymer compositions will then
transform into gels after a prescribed gel time. The gels that
contain almost 100% tab water will face the brine existing in the
fluid-producing formation under reservoir conditions. Finally, it
was observed that polymer composition No. 1 that was prepared in
tab water with brine placed on top gave gel that had delayed
syneresis for more than 100 hours, compared to the other two
polymers. This polymer gel has no added cross-linker and has a long
gelation time compared to the other two polymer gels (9.75 hrs. of
gel time compared to about 4.75 and 4.5 hours of gel time for the
other two polymer gels at 80.degree. C.).
[0039] Table 10 shows the gel stability and gel strength of polymer
gels prepared in 100% brine and aged at 80.degree. C. with brine on
top of them. Again, these gels were the least stable of all other
gels mentioned above. Polymer gel No. 1 syneresed the least, with
about 40% of water production after only 504 hours of aging at
80.degree. C., compared to 55% and 60% of water production for
polymer gels No. 11C+0.11% AA and No. 12D+0.11% AA,
respectively.
[0040] In summary, polymer gels prepared in 100% tab water are most
stable and the strongest gels when aged at 80.degree. C. for
extended periods of time. The gels second in stability are those
polymer gels prepared in 100% brine and stored at 80.degree. C. The
gels ranked third in stability are those gels prepared in 100% tab
water and stored at 80.degree. C. with brine on top of them. The
gels ranked fourth in stability are those gels prepared in 100%
brine and stored at 80.degree. C. with brine placed on top of them.
As for polymer gels, the most stable polymer gel is No. 1, followed
by 11C+11% AA and 12D+0.11% AA respectively.
Example 34
Gel Strength of Some Polymer Gels
[0041] The gel strength of various polymer compositions was
determined by static and dynamic techniques. Polymer compositions
Nos. 1, 1+0.11% AA, 11C+0.11% AA, and No. 12D+0.11% AA were tested
for their strength after gelling. The strength of these gels was
measured by using a Testometric mechanical testing machine. The
compositions were gelled in a tube with a diameter of about 27 mm.
The bottom of the tube is conical and has an orifice that was
drilled through, measuring 3 mm in diameter and 1.5 mm in length.
The tubes containing the gels were then compressed by applying a
plunger facing the gels and the gels were extruded at a constant
extrusion rate of 0.5 mm/min. The dynamic shear stress, force,
strain, and total deflections were recorded continuously. Table 11
shows the extracted data. These properties include the viscosity
and the modulus of elasticity in addition to the force needed to
extrude these gels at room temperature through an orifice of 0.3 cm
in diameter. The data shows that polymer composition No. 12D+0.11%
AA produces the strongest gels compared to the other polymer
compositions.
TABLE-US-00011 TABLE 11 Visco-elastic Properties of Extruded Gels
Stress** Viscosity Modulus of Polymer Force* Deflection*
.sigma..sub.c .eta. Elasticity E Comp. F, (Kg) Strain* (mm)
(kg/cm.sup.2) (cP) E (kg/cm.sup.2) (psi) 1 23.29 0.177 17.03 341.82
8.90E+9 1942.3 2.86E4 1 + 0.11% AA 19.51 0.202 19.36 277.02 7.50E+9
1372.5 2.02E4 11C + 0.11% AA 15.45 0.130 12.44 223.76 5.96E+9
1725.9 2.54E4 12D + 0.11% AA 37.10 0.104 9.93 528.12 14.3E+9 5101.7
7.5E4 *At peak in tube **At peak in capillary
[0042] Another experiment was also performed to test the gel
strength under static load conditions. The tubes containing the
gels were loaded with dead weights and stored at 80.degree. C.
Polymer compositions No. 1, 11C+0.11% AA, 12D+0.11% AA, 11C-1+3%
AA, 1-1+3% AA and 12D-1+3% A.A were first gelled, and an orifice
with diameter of 0.3 cm and length of 0.15 cm was drilled through
the bottom of the tube. A dead weight of 3.36 kg was replaced on
top of the gels for more than 240 hours at 80.degree. C. No gel
came through the orifice for polymer compositions Nos. 1, 11C+0.11%
AA, and No. 12D+0.11% AA after 240 hours of storage at 80.degree.
C. However, for gels made from 11C-1+3% AA, 80% of the gel did
extrude out after only 96 hours of storage at 80.degree. C. under
the same dead load of 3.36 kg. Similarly, for polymer composition
No. 1-1+3% AA, 20% of the gel extruded out after 96 hrs under a
static load of 3.36 kg (or 700 psi) at 80.degree. C. Polymer
composition No. 12D-1+3% AA extruded only 8% of the gel under the
same conditions. Some of the data and results are shown in Table
12. It should be noted that polymer composition 11C-1+3% AA is a
dilute version of polymer composition No. 11C+0.11% AA, where the
concentration of the former is about 18%, compared to 23%
concentration for the latter. Also polymer compositions No. 1-1+3%
AA and polymer composition 12D-1+3% AA are dilute versions of
polymer compositions No. 1 and No. 12D, respectively. Table 12
shows the results of this static dead weight test that amounts to
about 47.56 kg/cm.sup.2 of static stress.
TABLE-US-00012 TABLE 12 Gel Strength under Static Dead Weight
Polymer Gels (% gel extruded) Time Stored at 1-1 + 11C-1 + 12D-1 +
12D + 80.degree. C. (hrs. 3% AA 3% AA 3% AA 0.11% AA 0 0.0 0.0 0.0
0.0 48 0.0 0.0 0.0 0.0 72 0.0 0.0 0.0 0.0 96 20.0 80.0 8.0 0.0 120
20.0 -- 8.0 0.0 144 20.0 -- 8.0 0.0 240 20.0 -- 8.0 0.0
Example 35
Core Permeability Flooding System
[0043] Performance evaluation of some developed polymer
compositions as water shut-off treatments was carried out by using
Bench Top Permeability Flooding System (BPS-805). The BPS-805
system is a manually operated system designed for performing simple
liquid permeability tests at pore pressures up to 1500 psi. The
system is equipped with a pump, two transducers to measure the
pressure drop, a core holder, and a back pressure regulator. The
system is connected to computer software. It mainly consists of a
pump capable of delivering fluids at rates ranging from 0.01 cc/min
up to 100 cc/min, and with injection pressure up to 3000 psi. It
has a Hassler core holder mounted horizontally and can house cores
with 1.5 inch diameter and from one to four inches in length under
a confining pressure of up to 6000 psi. It is also equipped with
high accuracy differential pressure of 5000 psi transducer, and
1500 psi back pressure regulator. The core can be heated with
heating tapes, and the temperature is controlled by a digital
controller. Fluids can be injected directly through the pump or via
a cylindrical holder with piston-like drive and a capacity of 500
cc. A data acquisition system, consisting of software program,
plug-in interface card and cables, is also provided to control the
pump, monitor differential pressures and temperatures, and log all
pertinent data, while simultaneously calculating permeability
values that are displayed on a real-time graphical display.
Example 36
Sequences of Fluids in Core Flooding
[0044] Core flooding experiments with different fluids were carried
out for two cases. The first case is brine-polymer-brine (BPB), and
the second case is brine-oil-brine-polymer-brine-oil-brine
(BOBPBOB). The tests were conducted on cores of an oil-producing
well in West Kuwait (designated as Minagish MN-117 cores), and on
Berea sand cores of low and intermediate permeabilities. The cores
were routinely analyzed for pertinent data, such as weight, length,
diameter, pore volume, porosity, grain density, air permeability
and Klinkenberg permeability. The cores were saturated with 3% KCl
brine using a pressure saturator, and the saturation was done under
2000 psi. After saturation, the cores were weighed and the pore
volumes after saturation were measured to check the saturation
percentage. It was found that the cores were 100% saturated with 3%
KCl and ready for flooding.
Example 37
Main Properties of Core Flooding Fluids
[0045] All fluids were degassed before they were used for the
flooding experiments. Pertinent data, such as the density and
viscosity of the brine, oil, and the polymers, were measured and
fed into the system a priori. Before loading the core, the inlet
line to the core was flushed with brine. Then the core was loaded,
confining pressure was set to 2000-2500 psi, and back pressure was
set to around 600 psi. The core was held at 60.degree. C.,
80.degree. C., and 110.degree. C., which are the main test
temperatures.
[0046] Table 13 shows the physical properties of the three fluids
that were used for the core flooding experiments to evaluate the
effectiveness of the developed polymer compositions. The three
fluids are oil, 3% KCl brine, and the polymer composition No. 1,
with and without a cross-linker of acetic acid. Dynamic viscosities
at various temperatures ranging from 25.degree. C. to 80.degree.
C., along with their densities at 25.degree. C., are shown in the
table. The oil used in the evaluation is Habarah TIMA 600R, which
is thermally stable oil used at high temperatures as heating
oil.
TABLE-US-00013 TABLE 13 Fluids used for Water Shut-off Evaluation
Density at Dynamic Viscosity, (cP) Component 25.degree. C. (g/cc)
25.degree. C. 40.degree. C. 60.degree. C. 80.degree. C. Polymer
1.0676 578.05 403.92 212.87 124.13 Composition No. 1 Polymer 1.0659
713.18 447.64 282.69 171.75 Composition No. 1 + 0.22% AA Oil
(Habarah 0.8599 48 29.24 12.60 7.00 TIMA 600R) Brine (3% KCl)
1.0154 0.97 0.72 0.53 0.40
Example 38
Rheological Properties of Some Polymer Compositions Used for
(WSO)
[0047] Table 14 shows the viscosity of some polymer compositions
that were used for the performance evaluation as water shut-off
(WSO) polymer gels. These viscosities were measured at temperatures
ranging from 40.degree. C. to 80.degree. C. The viscosities shown
in the table correspond to a shear rate of 100 s.sup.-1. Also shown
in the table are the viscosities that are predicted, from curve
fitting equations, at 90.degree. C. and 110.degree. C. The
viscosities were measured using a Haake Rotational Viscometer. The
viscosities range between 4.8 cP to over 2105 cP when measured at
40.degree. C., and between 3.2 cP to 437.7 cP when measured at
80.degree. C.
TABLE-US-00014 TABLE 14 Rheological Properties of Polymers Used for
Water Shut Off Evaluation Acetic Acid Polymer Measured Viscosity at
Predicted Polymer Cross- Concentration 100 s.sup.-1(cP) Viscosity
(cP) Composition Linker (%) (%) 40.degree. C. 60.degree. C.
80.degree. C. 90.degree. C. 110.degree. C. 1 0.0 23.0 287.7 147.2
94 88.1 47.3 1-1 0.0 17.95 130.2 73.4 44.0 37.8 27.2 2.0 96.8 64.83
42.76 39.96 -- 3.0 104.4 66.56 56.30 41.00 -- 1-2 0.0 10.72 26.2
15.6 10.3 8.9 6.7 1-3 0.0 6.04 6 4.6 4.1 3.9 3.7 11 0.0 32.0 340
152.5 117.75 97.3 81.2 11C 0.0 24.0 42 32 24 19.2 16.6 0.05 88.8
47.6 36.20 27.9 21.3 0.11 73.67 42.90 30.76 25.67 -- 11C-1 0.0
17.65 22.5 14.22 10.10 9.10 -- 2.0 24.6 15.7 12.60 11.80 -- 3.0
25.0 17.0 .15.2 -- -- 11C-2 0.0 10.65 7.4 5.5 4.5 3.9 3.3 11C-3 0.0
6.32 4.8 3.9 3.2 3.4 3.2 12 0.0 22.68 2105 1089 418.5 339.9 163.44
12D 0.0 20.2 800.6 252.8 97 87.8 30.37 0.11 1044 335.7 170.3 -- --
12D-1 0.0 18.25 672.4 221.9 88.6 45.7 15.6 2.0 -- -- -- -- 3.0 800
458 404 -- -- 12D-2 0.0 9.24 35.2 15.8 9.4 7.4 5.1 12D-3 0.0 6.25
9.8 6.5 4.9 4.4 3.6
Example 39
Results of Performance Evaluation of Some Polymer Gels
[0048] The results that were obtained from the evaluation of some
of the developed polymer compositions utilizing the (BPS-805)
system are outlined below. The polymer compositions that were
chosen for the evaluation are concentrated polymer compositions No.
1, No. 1+0.22% AA, No. 11, No, 11C+0.11% AA, No. 12, No. 12D+0.11%
AA, and 12+0.05% AA, and the dilute forms of No. 1, No. 11C+0.11%
AA and No. 12D+0.11% AA. The main characteristics of these polymer
compositions, such as density, dynamic viscosity at various
temperatures, 100% gelation time with and without a cross-linker,
their gel elasticity at various test temperatures ranging from
60.degree. C.-110.degree. C., their gel elasticity characteristics
upon aging at 80.degree. C., and their stability were disclosed
above. Two core flooding cases were studied in the evaluation. The
first case assumes a formation that produces only water. Hence, a
flooding sequence of brine-polymer-brine (BPB) was carried out for
Minagish MN-117 cores of intermediate permeability (1020 mD-3320
mD) and for Berea sand cores of low permeability (68 mD-126 mD) and
of intermediate permeability (1700 mD-2700 mD). The second core
flooding case assumes that a formation produces both oil and brine.
Hence, a sequence of injection of
brine-oil-brine-polymer-brine-oil-brine (BOBPBOB) was conducted for
a number of cores. This second case was repeated for different
polymer pore volumes, followed by several cycles of reverse
flooding. For example, a fluid injection sequence of
brine-oil-brine-polymer-brine-oil-brine-polymer-brine-oil-brine-polytner--
brine-oil (BOB-P-BOB-P-BOB-P-BO) was carried out in both the
forward direction and the reverse direction. Each cycle consists of
30 minutes for brine flooding, followed by 30 minutes of oil
flooding, for a total flooding time of 1 hour for each cycle.
[0049] As for Minagish MN-117 cores, the first case of core
flooding (BPB) was carried out. Brine was flooded at a rate of 20
cc/min, and 178.65 pore volumes of brine were injected until
stabilization was reached. The measured permeability to brine was
1231.47 mD and differential pressure was 1.05 psi. Polymer
composition No. 1+0.22% AA was then injected at a rate of 10 cc/min
to cover 0.7 pore volume of the core, and then the core was shut-in
for about 22 hours at 70.degree. C. After 22 hours of shut-in at
70.degree. C. permeability to brine dropped to 123.74 mD and
differential pressure was 4.49 psi. Directly after flooding with
brine, 1.31 pore volume of the polymer was injected again at a rate
of 2 cc/min. Then the core was shut-in for about 22 hours at
70.degree. C. Brine was then injected at a rate of 10 cc/min; a
total of 64.90 pore volumes were injected. Permeability to brine
dropped to 12.38 mD, and the differential pressure was 41.39 psi. A
1.92 pore volume of the polymer was then injected at a rate of 2
cc/min. Then the core was shut-in for about 22 hours at 70.degree.
C. Brine was injected at a rate of 10 cc/min and continued till the
pressure build-up reached 3000 psi, which is the maximum pressure
of the pump, and no fluid was coming out from the core, which
indicates that a total water shutoff was achieved. Permeability
reduction to brine, which is defined as
(K.sub.ab-K.sub.wi)/K.sub.ab, was calculated to be 89.95% for 0.7
polymer pore volume injected and 98.99% for 1.31 polymer pore
volume injected, and finally, 100% permeability reduction to brine
or a total water shut-off was achieved for a polymer pore volume of
1.92 when tested at 70.degree. C. and for the first case of
flooding (BPB).
[0050] For the second case, where brine, oil and polymer (BOBPBQ)
were injected in the MN-117 core with initial permeability to brine
of 1165 mD, again almost a 100% water shutoff was achieved at 1.0
pore volume of polymer no. 1+0.11% AA, and about 96% of
permeability reduction to oil was achieved when tested at
70.degree. C. After the core was treated with the polymer no.
1+0.22% AA in the presence of irreducible water and residual oil,
the forward flooding and reverse flooding of oil show no difference
in the permeability reduction to oil.
[0051] When a MN-117 core with initial absolute permeability to
brine of 531.5 mD is saturated with irreducible brine and residual
oil treated with subsequent pore volumes of polymer composition No.
1+0.22% AA, the permeability reduction to brine is almost 80% for
brine and about 3.0% reduction for oil when only about 0.2 PV of
polymer was injected and tested at 70.degree. C. Also, at 0.45 PV
of polymer no. 1+0.22% AA treatment, the permeability reduction to
brine is about 96%, while for oil, it is about 30%.
Example 40
Effect of EAC Pre-Flushing with (BPB) Flooding Sequence
[0052] Pre-flushing the Berea sand cores (1700 mD-2700 mD) with
ethyl acetate (EAC) prior to polymer treatment in the first case of
flooding sequence (BPB) doesn't improve the degree of water
shutoff, and it weakens the treatment so that the pressure
breakthrough is half that of the case where there is no pre-flush
and the end permeability is higher, indicating less water shutoff.
Pre-flushing the Berea sand core with EAC prior to injecting 0.66
PV of concentrated polymer composition No. 1+0.22% AA results in
final permeability to brine, breakthrough pressure and residual
resistance factor of 0.12 mD, 530 psi, and 9883, respectively,
compared to the no pre-flush case where only 0.39 PV of polymer no.
1+0.22% AA was injected, where the corresponding values were 0.048
mD, 1000 psi, and 24,708, respectively, when tested at 80.degree.
C. The same trend of chemical pre-flush with EAC was also observed
when polymer solutions No. 11 and No. 12 were used at almost the
same dose of treatment for Berea sand cores with intermediate
permeability, and when all were tested at 80.degree. C. for the
first case of flooding sequence (BPB).
Example 41
Effect of EAC Pre-Flushing with (BOBPBO-) Flooding Sequence
[0053] For the second case, where brine and oil were used as core
flooding media (BOBPBO-), the effect of EAC pre-flush prior to
polymer treatment of Berea sand cores (1700 mD-2700 mD) tends to
give more permeable cores and less water shutoff, where the final %
permeability reduction to brine and to oil after 8 cycles of
reverse flooding for treated cores with about 0.48 PV of
concentrated polymer compositions and tested at 80.degree. C. were:
84.64% and 27.52%, respectively, for polymer composition No. 1, and
they were 70.96% and 18.07%, respectively, for polymer composition
No. 11C+0.11% AA, and they were 78.35% and 38.72%, respectively,
for polymer composition No. 12D+0.11% AA. On the other hand, almost
a total water shutoff was achieved when there was no chemical
pre-flush prior to the same dose of polymer treatment. It is
possible that the presence of EAC with polymer compositions delays
the gelation time of these compositions, where for polymer solution
no. 1, the gelation time increased from 4.5 hours to 14.0 hours
when EAC was present in the polymer solution and tested at
80.degree. C. Therefore, more shut-in time should be allowed for
gelation to take place whenever EAC is present.
Example 42
Effect of Polymer Concentration on their Gel Performance
[0054] The effect of the polymer composition concentration on their
performance was also tested. Therefore, core flooding tests were
conducted on both the concentrated and the diluted polymer
compositions for two cases of flooding, namely, for Case (1)
Brine-polymer-Brine (BPB), and for Case (2)
Brine-oil-brine-polymer-brine-oil (BOBPBO-), at three temperatures
of 60.degree. C., 80.degree. C. and 110.degree. C., with and
without chemical pre-flush using MN-117 cores with permeabilities
that range from 1020 mD to 3320 mD and Berea sand cores of low
permeability (69 mD-126 mD) and intermediate permeability (1700
mD-2700 mD).
[0055] When concentrated polymer compositions No. 1, No. 11C+0.11%
AA, and no. 12D+0.11% AA were used to treat Berea sand cores (1700
mD-2700 mD) with about 0.5 PV of the composition, these polymers
gave a high rate of oil recovery and very high permeability to oil,
while all of them gave a very low rate of water recovery and very
low permeability to brine after nine reverse flooding cycles at
80.degree. C. For example, the final permeability reduction to
brine was 78.64%, compared to only 11.75% permeability reduction to
oil when polymer composition #12D+0.11% AA at 0.5 PV treatment was
used at 80.degree. C. When the diluted version of these polymer
compositions was used to treat the same permeability Berea sand
cores with 1.0 PV of these polymers, the % permeability recovery to
brine at 80.degree. C. was 4.51%, 9.26% and 20.48%, respectively,
for polymer compositions no. 1-1+3% AA, no. 11C-1+3% AA, and no.
12D-1+3% AA, respectively. Similarly, the % permeability recovery
to oil was 44.95%, 73.44%, and 91.95%, respectively, for the same
polymers, indicating that about 1.0 PV of diluted polymers is as
effective as 0.5 PV of the concentrated version of these polymers.
Similar behavior was also observed when both the concentrated and
diluted polymer compositions were tested at 60.degree. C., where
0.50 PV of the diluted solutions is equivalent to 0.25 PV or less
of the concentrated polymer compositions.
[0056] Concentrated polymer composition no. 11C+0.11% AA was used
to treat low permeability Berea sand core (69 mD-126 mD) with 0.387
PV treatment, which gave almost the same degree of water shut off
of 96.34%, and the permeability to oil was 78.14%, when tested at
80.degree. C.
Example 43
Effect of Sequential Treatment with Diluted and Concentrated
Polymer Compositions on their Performance
[0057] The effect of combined sequential injection of diluted and
concentrated polymers for water shutoff was also tested. A combined
sequential injection or treatment of diluted polymer compositions
with their concentrated counterparts produces effective water
shut-off treatment when they were tested for the second case of
core flooding (BOBPBO) at 110.degree. C. For example, 0.75 PV of
concentrated polymer No. 1 treatment gave almost the same effect as
the second treatment that consisted of 0.5 PV of its diluted
version (polymer No. 1-1+3% AA) plus 0.25 PV of its concentrated
form (polymer No. 1), where % reduction to brine permeability
ranged from 78.8% to 84.62%, while for oil the % reduction was
24.22% to 29.73% for the two treatments, respectively. A similar
trend was also found to be true when concentrated and diluted
polymers were used in the brine-polymer-brine (BPB) case, where 0.5
PV of concentrated polymer treatment is equivalent to almost 1.0 PV
of diluted polymer compositions treatment when tested at 80.degree.
C. with Berea sand cores, where the % permeability reduction to
brine ranged from 91%-99% for the concentrated polymers, compared
to a range of 64%-87% for the diluted versions.
Example 44
Effect of Shut-in Conditions of Some Polymer Gels on their
Performance
[0058] Shut-in times and conditions of shut-in do affect the
performance of both the diluted and concentrated polymer
compositions performance as water shut-off treatments. Shut-in
times should be at least two to three times the laboratory-measured
gelation time, and the conditions of shut-in should be similar to
reservoir conditions (i.e., similar pressure and temperature). For
example, when 0.26 PV of polymer composition No. 1 was injected
into Berea sand core at 80.degree. C., the core was shut-in for 17
hours at 60.degree. C. and 1500 psi, followed by another 24 hours
at 80.degree. C. at atmospheric pressure, so that the brine and oil
% permeability reduction was 98.8% and 87.78%, respectively,
compared to the same treatment by the second shut-in condition that
was 41 hours at 60.degree. C. and at 1500 psi only, so that the
corresponding % permeability reduction to brine and oil were 98.29%
and 73.85%, respectively. Similar behavior was also observed for
other diluted and concentrated polymer compositions. For example
when 1.05 PV of diluted polymer composition No. 1-1+3% AA was
injected and the treated Berea core was shut-in at 80.degree. C.
for 17 hours and 1500 psi, followed by 24 hrs. at the same
temperature and at atmospheric pressure, the resulting %
permeability reduction to brine and oil were 97.22% and 83.91%,
respectively, compared to the second case of shut-in, where the
core was kept at 80.degree. C. and 1500 psi for 41 hrs, which gave
% permeability reduction to brine and oil of 95.49% and 55.05%,
respectively.
Example 45
Effect of Thermal Ageing on the Performance of Polymer Gels
[0059] The effect of thermal aging conditions on the performance of
concentrated and diluted polymer compositions on the water shut-off
of treated Berea sand cores was investigated. Low permeability
Berea sand cores (69-126 mD) were treated with. 0.25 PV of
concentrated polymer compositions No. 1, No. 11C+0.11% AA, and
12D+0.11% AA at 80.degree. C. The treated cores were tested for the
% permeability recovery to oil and brine after they have been aged
for more than 4 months in oil that was kept at 80.degree. C. and
under a pressure of700 psi. The results show that no appreciable
change in their performance as water shut-off gels took place. For
example, for the three polymers tested, % permeability recovery to
brine changed from about 1.14% to 4.00% for polymer No. 1 after 150
days of aging. Similarly, for polymer No. 11C+0.11% AA, the %
recovery to brine changed from 0.32% to 6.67% after 144 days of
aging. Finally, for polymer No. 12D+0.11% AA, the % permeability
recovery to brine changed from 0.97% to 6.25% after 128 days of
aging. The same trend was also observed for % permeability recovery
to oil. For example, aging of Berea sand core samples treated with
1.0 PV of the diluted version of the above concentrated polymer
compositions (i.e., 1-1+3% AA, No. 11C-1+3% AA, and No. 12D-1+3%
AA) and aged at the same conditions as above and tested at
80.degree. C. have shown significant changes in % permeability
recovery to oil where it was above 90%, while maintaining %
permeability recovery to brine of about 20% when tested at
80.degree. C. Finally, the effect of aging was evaluated at
110.degree. C., and the results show that for treated Berea sand
cores with 0.75 PV of concentrated polymer compositions (polymer
No. 1, No. 11C+0.22% AA, and no. 12D+0.22% AA) and that were aged
for 35 days at 80.degree. C. and 700 psi and fully immersed in oil,
the % permeability recovery for brine increased from 20% to about
30%, and % permeability recovery for oil approaches about 100% when
tested at 110.degree. C. for all the polymer compositions.
Example 46
Effect of Formation Composition on Performance of the Polymer
Gels
[0060] The effect of formation composition and makeup on the
performance of both the diluted No. 11C-1+3% AA and concentrated
No. 11C+0.11% AA polymer composition samples were evaluated. Low
permeability cores of Berea sandstone (67 mD) and Limestone (45 mD)
taken from Sabrieh Oil Field-Northern Kuwait were flooded with
different pore volumes of the two polymer compositions at
80.degree. C., and with the second case of flooding sequence where
oil and brine were used (BOBPBO). The results in Table 15 show the
effect of different pore volumes (PV) on the % permeability
reduction of brine and oil. The results show that diluted polymer
compositions are more suited to be used with a low permeability
formation, regardless of its makeup and composition. This is true
because diluted polymers give significant permeability reduction to
water with insignificant permeability reduction to oil. Also, the
results show that both sandstone and limestone behave the same way
with the two polymer systems.
TABLE-US-00015 TABLE 15 Effect of pore volume (PV) of polymer
compositions on the % permeability reduction of low permeability
Berea Sandstone (67 mD) and Limestone (45 mD) cores Berea Sandstone
Limestone (67 mD) (45 mD) Polymer PV Brine Oil Brine Oil Sample
Injected (% K.sub.W) (% Ko) (% Kw) (% Ko) 11C + 0.11% AA 0.10 72.86
50.00 73.53 38.89 Conc. = 23% 0.15 88.00 66.00 78.65 46.51 0.20
96.89 77.63 91.76 65.56 0.25 99.69 94.79 98.65 88.95 11C-1 + 3% AA
0.10 53.0 13.00 52.00 5.00 Conc. = 18% 0.15 72.5 19.32 70.27 7.89
0.20 80.0 23.00 75.00 11.00 0.25 81.0 28.00 76.00 16.50 0.30 82.5
30.68 77.70 18.47
[0061] The polymer gel as described herein is applicable in
retarding fluid flow of water from subterranean oil and gas
reservoirs and in treating high permeability zones that produce
this water. These cases include, but are not limited to, natural
and man-made fractures, channeling, shale streaks, fingering, water
coning, micro-cracks, and others. The new polymer gelants/gels can
be used for both fractured and matrix of oil and gas wells in
subterranean formation of sandstone and limestone. By using these
polymer compositions that can transform from solutions to gelants
to gels, a total water shutoff is possible after a predetermined
period of gelation time, selecting predetermined gel properties
depending on the needs of the formation zone to be treated. These
gels do not enter low permeability zones, which leads to
insignificant effect on the productivity of the oil and gas.
Therefore, the polymer composition can be used as a water shut-off
polymer gel or as a blocking agent, and can also be used as a
relative permeability modifier for all types of subterranean
formations, including sandstone formations and carbonate or
limestone formations.
[0062] 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.
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