Crosslinking of swellable polymer with PEI

Abstract

The invention is directed to stable and labile crosslinked water swellable polymeric microparticles that can be further gelled, methods for making same, and their various uses in the hygiene and medical arts, gel electrophoresis, packaging, agriculture, the cable industry, information technology, in the food industry, papermaking, use as flocculation aids, and the like. More particularly, the invention relates to a composition comprising expandable polymeric microparticles having labile crosslinkers and stable crosslinkers, said microparticle mixed with a fluid and an unreacted tertiary crosslinker comprising PEI or other polyamine based tertiary crosslinker that is capable of further crosslinking the microparticle on degradation of the labile crosslinker and swelling of the particle, so as to form a stable gel. A particularly important use is as an injection fluid in petroleum production, where the expandable polymeric microparticles are injected into a well and when the heat and/or pH of the well cause degradation of the labile crosslinker and when the microparticle expands, the tertiary crosslinker crosslinks the polymer to form a stable gel, thus diverting water to lower permeability regions and improving oil recovery.

Claims

1. A method of increasing the recovery of hydrocarbon fluids in a subterranean formation, comprising: a. injecting into the subterranean formation a mixture comprising a brine and expandable nonionic acrylamide-based polymeric microparticles having labile crosslinkers and stable crosslinkers, said labile crosslinkers are PEG-200 diacrylate or PEG-400 diacrylate, and said stable crosslinker is methylene bis-acrylamide, wherein the brine is: TABLE-US-00002 Brine Composition Bicarbonate  1621 ppm Chloride 15330 ppm Sulfate  250 ppm Calcium  121 ppm Potassium  86.9 ppm  Magnesium  169 ppm Sodium 11040 ppm Strontium  7.57 ppm  b. injecting an unreacted tertiary crosslinker into the subterranean formation that further crosslinks said expandable acrylamide-based polymeric microparticle by transamidation, wherein said tertiary crosslinker is 1000 ppm of polyethyleneimine (“PEI”); c. aging said mixture at 190° C. until it forms a stable gel that can withstand pressure of up to 1000 psi; and, d. producing hydrocarbon from said subterranean formation.

2. The method of claim 1, wherein steps a) and b) occur at different times or the same time.

3. The method of claim 1, wherein said mixture further comprises a tertiary crosslinker retarder or a carbonate retarder.

4. The method of claim 1, wherein said nonionic acrylamide-based polymeric particles are polyacrylamide particles.

5. A method of increasing the recovery of hydrocarbon from a reservoir, comprising: a. obtaining a dry powder mixture comprising i) expandable microparticle kernels comprising nonionic acrylamide-based polymers crosslinked with labile crosslinkers and stable crosslinkers, plus ii) an unreacted tertiary crosslinker consisting of PEI; b. mixing said dry powder mixture with a fluid to form a kernel suspension; c. injecting said kernel suspension into a reservoir containing hydrocarbon; d. degrading the labile crosslinker and expanding said expandable microparticle kernels to form expanded polymer; e. covalently crosslinking said expanded polymer by transamidation with 1000 ppm PEI to form a stable gel having a viscosity of 700 centipoise that can withstand pressure of up to 1000 psi; f. injecting a fluid into said reservoir to sweep hydrocarbon towards a production well; and g. producing hydrocarbon from said production well.

6. The method of claim 5, wherein said nonionic acrylamide-based polymers are polyacrylamide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1. Transamidation of the amide group.

(2) FIG. 2. Results of Slim Tube testing of the BrightWater® polymer.

(3) FIG. 3. Viscosity versus Aging Time for 0.5% BrightWater® EC 9408A with (black diamonds) or without (hollow diamonds) 1000 ppm PEI (25 KD), which was prepared in Brine A and aged at 190° F.

(4) FIG. 4. Viscosity versus Aging Time for 0.5% BrightWater® EC 9408A with (black square) or without (hollow square) 1000 ppm PEI (25 KD), which was prepared in Brine A and aged at 150° F.

(5) FIG. 5. Viscosity versus Aging Time for 0.5% BrightWater® EC 9408A with (black shapes) or without (hollow shapes) 1000 ppm PEI (25 KDa), which was prepared in Brine A and aged at 150° F. and 190° F.

(6) FIG. 6. Viscosity versus aging time for an anionic polymeric microparticle and 1000 ppm PEI prepared in synthetic Brine A and aged at 150° F. (triangles) and 190° F. (diamonds). The anionic polymeric microparticle is a swellable copolymer of acrylamide and sodium acrylate crosslinked with poly(ethylene glycol) (258) diacrylate and methylene bisacrylamide.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(7) The invention provides a novel polymer that swells on a stimulus and is then additionally crosslinked in situ to form a gel. Such smart gels have particular utility in sweeping reservoirs, but many uses are possible.

(8) Extensive experiments performed with an expandable polymer, as described in U.S. Pat. Nos. 6,454,003, 6,729,402 and 6,984,705, demonstrated that this polymer swells as a result of aging at elevated temperature or exposure to acidic or caustic conditions. The copolymer of acrylamide and sodium AMPS is crosslinked with two crosslinkers. The first crosslinker is a stable crosslinker such as methylene bis-acrylamide in the range of 1-300 ppm, while the second crosslinker is a labile (unstable) compound such as PEG-200, or PEG-400, a diacrylate crosslinker that breaks down when exposed to high temperatures or changes in pH. The resulting doubly-crosslinked polymer results in a small particle size, ranging at 0.05 to 10 microns.

(9) Such small particle polymers exhibit very low viscosity when suspended in water, a desirable property that improves injectivity, for treating high permeability zones deep in oil bearing formations. These low viscosity (water-like) micro-particle solutions are injected into the thief zones of the reservoirs with very little pressure requirement for penetration.

(10) If the reservoir temperature is high enough, or another suitable stimulus is applied, the labile crosslinker undergoes hydrolysis and breaks down allowing the microparticle or “kernel” to expand or “pop,” thus increasing the viscosity of the solution. The resulting “popped” polymer diverts the subsequent water injection away from the thief zones into lower permeability oil zones to produce additional oil.

(11) Experiments performed with these micro-particles injected into 40′ slim tubes packed with sand showed impressive resistance factors in all eight 5′ sections of the slim tubes after aging at elevated temperatures (150-190° F.). However, our research also indicated that resistance to flow of water gradually diminished with additional water injection indicating polymer wash-out in porous media—a highly undesirable property. See e.g., FIG. 2.

(12) We therefore undertook to prevent wash-out of expandable polymers, and discovered that when PEI was combined with the above swellable polymer, the resulting gel remained extremely stable to washout, even at high pressure!

(13) The function of the PEI tertiary crosslinker in this application is not proven, but probably uses a mechanism similar to the following: The unswelled microparticles contain a copolymer of acrylamide and sodium AMPS, which is doubly crosslinked with methylene bis-acrylamide as a permanent crosslinker and PEG-200 or PEG-400 diacrylate, as a labile or unstable crosslinkers. These micro-particles are in a ball form and cannot be further crosslinked since the functional groups are mostly hidden inside these microparticles.

(14) After the polymer reaches the target zone deep in the reservoir, the unstable internal crosslinkers PEG-200 or PEG-400 diacrylates hydrolyze, and the particle then opens up (swells or “pops”). Such popped particles behave as a typical polymer exhibiting good viscosities, but they are not gels. The addition of the tertiary PEI crosslinker, crosslinks the now accessible amide groups and results in a stable gel in situ.

(15) Slim tube tests were performed to determine the performance of BrightWater® type polymers in porous media when crosslinked in situ with the PEI tertiary crosslinker. Each tube was composed of eight 5′ long stainless steel tubing with internal diameter (i.d.)=⅜″. The sections were filled with sand before connecting each to a pressure tap and assembling them together and forming a coil from them for ease of handling. The coil was then placed in an oven set to a desired temperature. Flow rates and differential pressure measurements were monitored by a LabVIEW data acquisition system throughout the experiment.

(16) Each test required three Isco 500D syringe pumps. One pump was used to maintain a back pressure of 100 psi on the slim tube. The second pump was used for water injection, and the third pump was used for polymer injection. These pumps were programmed to inject or withdraw at a given flow rate while monitoring the pressure.

(17) The test was initiated by water injection at constant flow rates to determine permeability in each section of the slim tube. About 1-2 pore volume (PV) polymer solution was then injected into the slim tube at constant flow rate followed by a small amount of water injection to clear the inlet lines from polymer. Simultaneously 6 ampoules containing the polymer solution were placed in the same oven to monitor the progress of popping process.

(18) Popping time is a strong function of aging temperature—that is the higher the temperature, the shorter the popping time. In order to determine the optimum aging condition, we accelerated aging of the polymer at 190° F. to shorten the popping time. After varying aging times at 190° F. or 150° F., the resistance factor was determined by injecting a small amount of water. At the same time the content of one ampoule was used to determine the viscosity and extent of polymer popping.

(19) The brine composition used in the experiments is given in Table A.

(20) TABLE-US-00001 TABLE 1 Brine A Composition Bicarbonate ppm 1621 Chloride ppm 15330 Sulfate ppm 250 Calcium ppm 121 Potassium ppm 86.9 Magnesium ppm 169 Sodium ppm 11040 Strontium ppm 7.57

(21) FIG. 3 shows the viscosity versus aging time for 0.5% BrightWater® EC 9408A microparticles with and without 1000 ppm PEI aged at 190° F. in brine A. As this graphic shows, the solution of polymer alone reached a maximum viscosity of about 67 centi Poise (cP) within 11 days of aging with no appreciable change with additional aging at 190° F. However, the same microparticles solution containing 1000 ppm PEI (identified as “gelant”) began to gel within a few days of aging at 190° F.

(22) A similar experiment performed with this system aged at 150° F. resulted in gel formation at longer aging times. FIG. 4 shows a plot of viscosity versus aging time at 150° F. for a solution of 0.5% BrightWater® EC 9408A microparticles achieving a maximum viscosity of about 57 cP in 51 days of aging. A similar solution containing 0.5% BrightWater® EC 9408A and 1000 ppm PEI (identified as “gelant”) began to gel in about 28 days of aging at 150° F.

(23) FIG. 5 shows composite plots of FIGS. 3 and 4 indicating gel formation when the polymer contains PEI and aged at 150° F. or 190° F. The difference is the longer tertiary gelation time at the lower temperature. Gelation time can also be increased with the addition of a carbonate retarder.

(24) Earlier experiments performed in a slim tube treated with BrightWater® microparticles and phenol/formaldehyde crosslinking systems also produced strong gels. The resulting gel effectively prohibited water flow in such tube even at pressures as high as 1000 psi. Such gels essentially consolidated the sand, which could not be pushed out of the tube unless it was cut in small segments (2-3″) and exposed to very high pressures (˜1000 psi). Our experiments herein with the PEI tertiary crosslinker also produced very strong gels, but differed in that PEI is less toxic to the environment. Further, PEI being a single component avoids any risk of separation, whereas phenol/formaldehyde might separate due to chromatographic separation.

(25) A final experiment is shown in FIG. 6, which compares viscosity versus aging time for an anionic polymeric microparticle that is a swellable copolymer of acrylamide and sodium acrylate crosslinked with poly(ethylene glycol) diacrylate and methylene bisacrylamide and including 1000 ppm PEI (MW 2000). The polymeric particles were aged in synthetic Brine A. As illustrated in FIG. 6, temperature affects gelation rate, increasing temperature increasing gelation rate.

(26) In summary, addition of polyethyleneimine to BrightWater® or anionic polymeric microparticles result in gelation of the popped polymer, when exposed to stimulants such as heat or pH changes. This process is expected to improve the longevity of BrightWater® or other swellable microparticle treatments. While gelation of PHPAM or other acrylamide based polymers with polyethyleneimine is well known, gelation of swellable microparticles with PEI is a novel process with the distinct advantage of low injection viscosity and in situ formation of gels which increase the longevity of BrightWater® and similar treatments.

(27) These experiments proved that the longevity of BrightWater® and similar polymer treatments could be significantly enhanced by addition of an external tertiary crosslinking system to the injection package. In these treatments, PEI tertiary crosslinking system produced gels with the popped polymer exhibiting very large RF values. The resulting gels are not mobile and cannot be washed out of the slim tube. Such gels actually behaved as binding agents consolidating the sand. Furthermore, the compositions described herein have many uses in other industries.

(28) Each of the following references is incorporated herein in their entirety for all purposes. U.S. Pat. No. 4,773,481 U.S. Pat. Nos. 6,454,003, 6,729,402, 6,984,705 US2010234252 Crosslinked Swellable Polymer US2010314115 Swellable polymer with cationic sites US2010292109 Swellable polymers with hydrophobic groups US2010314114 Swellable polymer with anionic sites SPE139308 Laboratory Development and Successful Field Application of a Conformance Polymer System for Low-, Medium- and High-Temperature Applications. SPE97530 Investigation of—A High Temperature Organic Water-Shutoff Gel: Reaction Mechanisms