DELAYED GELATION OF POLYMERS

Abstract

The disclosure is directed to methods and compositions delaying the gelation of polymers in water flooding by sequentially or co-injecting a carboxylate-containing polymer solution, a gel-delaying polymer, and gelation agent into a hydrocarbon reservoir. Delays of weeks are observed.

Claims

1. A delayed gelling composition, said composition made by: a) sequentially combining ingredients comprising: i) an expandable polymeric particle in injection fluid, said particle comprising a copolymer of about 80-98 mole percent acrylamide and about 2-20 mole % sodium acrylate; ii) at least one gel-delaying polymer; and iii) a crosslinker; b) thereby forming a delayed gelling composition without forming a separate nanogel.

2. The delayed gelling composition of claim 1, wherein said gel-delaying polymer has a gelation time of at least 30 days at 85° C. before a non-flowing gel is set.

3. The delayed gelling composition of claim 1, wherein said crosslinker is a multivalent metal ion selected from chromium, zirconium, iron, aluminum, and titanium.

4. The delayed gelling composition of claim 1, wherein said crosslinker is polyethylenimine (PEI).

5. The delayed gelling composition of claim 1, wherein said gel-delaying polymer is made from monomers selected from the group of vinyl, allyl, styrene, and acrylamide monomers and their derivatives, conjugated with a dicarboxylate or a tricarboxylate.

6. The delayed gelling composition of claim 1, wherein said gel-delaying polymer is polyvinyl alcohol succinate (PVAS), N-hydroxymethyl N-hydroxylmethyl acrylamide (NHMA) succinate, allyl alcohol succinate and allylamine succinate, PVA malate, NHMA malate, allyl alcohol malate or allylamine malate.

7. The delayed gelling composition of claim 1, wherein said gel-delaying polymer is carboxylated polymer polyaspartate (PAsp), polymalate, polyoxalate, polymalonate, polyglutarate, polyadipate, or polypimelate.

8. The delayed gelling composition of claim 1, wherein said gel-delaying polymer is PAsp and said crosslinker is Cr(III).

9. The delayed gelling composition of claim 1, wherein said gel-delaying polymer is PVAS and said crosslinker is Cr(III).

10. The delayed gelling composition of claim 1, wherein said expandable polymeric particle, said at least one gel-delaying polymer, and said crosslinker together form a complex.

11. The delayed gelling composition of claim 10, wherein said complex comprises PVAS or PAsp as the gel-delaying polymer and Cr(III) as the crosslinker.

12. The delayed gelling composition of claim 1, wherein said expandable polymeric particle comprises a copolymer of about 95 mole percent acrylamide and about 5 mole % sodium acrylate.

13. The delayed gelling composition of claim 10, wherein said expandable polymeric particle comprises a copolymer of about 95 mole percent acrylamide and about 5 mole % sodium acrylate.

14. A method of increasing the recovery of hydrocarbon fluids in a subterranean formation comprising: a) injecting the delayed gelling composition of claim 1 into a subterranean formation, wherein said gel-delaying polymer delays the gelation of said expandable polymeric particle by said crosslinker in said subterranean formation; b) injecting fluid into said subterranean formation to displace said delayed gelling composition deeper into said subterranean formation; c) waiting for said delayed gelling composition to gel; and then d) sweeping said reservoir for oil and producing said oil.

15. A method of increasing the recovery of hydrocarbon fluids in a subterranean formation comprising: a) injecting the delayed gelling composition of claim 8 into a subterranean formation, wherein said gel-delaying polymer delays the gelation of said expandable polymeric particle by said crosslinker in said subterranean formation; b) injecting fluid into said subterranean formation to displace said delayed gelling composition deeper into said subterranean formation; c) waiting for said delayed gelling composition to gel; and then d) sweeping said reservoir for oil and producing said oil.

16. A method of increasing the recovery of hydrocarbon fluids in a subterranean formation comprising: a) injecting the delayed gelling composition of claim 9 into a subterranean formation, wherein said gel-delaying polymer delays the gelation of said expandable polymeric particle by said crosslinker in said subterranean formation; b) injecting fluid into said subterranean formation to displace said delayed gelling composition deeper into said subterranean formation; c) waiting for said delayed gelling composition to gel; and then d) sweeping said reservoir for oil and producing said oil.

17. A method of increasing the recovery of hydrocarbon fluids in a subterranean formation comprising: a) injecting the delayed gelling composition of claim 12 into a subterranean formation, wherein said gel-delaying polymer delays the gelation of said expandable polymeric particle by said crosslinker in said subterranean formation; b) injecting fluid into said subterranean formation to displace said delayed gelling composition deeper into said subterranean formation; c) waiting for said delayed gelling composition to gel; and then d) sweeping said reservoir for oil and producing said oil.

18. A method of increasing the recovery of hydrocarbon fluids in a subterranean formation comprising: a) injecting the delayed gelling composition of claim 13 into a subterranean formation, wherein said gel-delaying polymer delays the gelation of said expandable polymeric particle by said crosslinker in said subterranean formation; b) injecting fluid into said subterranean formation to displace said delayed gelling composition deeper into said subterranean formation; c) waiting for said delayed gelling composition to gel; and then d) sweeping said reservoir for oil and producing said oil.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] FIG. 1A Water flooding wherein water bypasses oil, travelling the thief zones. FIG. 1B The thief zones can be blocked by polymeric gels, foam gels, and the like, thus forcing water to sweep the reservoir and producing more of the original oil in place.

[0054] FIG. 2. Complex formation of HPAM/B29 with PAsp/PVAS and Cr(III).

[0055] FIG. 3. Gelation of AC24, PAsp, and CrCl.sub.3 in Synthetic Brine A at 120, 100, and 85° C.

[0056] FIG. 4. Gelation of B29, PAsp, and CrCl.sub.3 in Synthetic Brine B at 120, 100, and 85° C.

[0057] FIG. 5. Gelation of AC24, PVAS, and CrCl.sub.3 in Synthetic Brine A at 85 and 65° C.

[0058] FIG. 6. Gelation of B29, PVAS, and CrCl.sub.3 in Synthetic Brine B at 85 and 65° C.

DETAILED DESCRIPTION

[0059] The disclosure provides a novel method that delays gelling under the conditions typical of water flooding in situ and have particular utility in blocking thief zones of reservoirs, but other uses are possible, especially in the agriculture, remediation and drug delivery arts.

[0060] In one embodiment, the method involves sequentially injecting a carboxylate-containing polymer, a gel-delaying polymer, and a crosslinker into the reservoir. This injection sequence negates the need to form a separate nanogel comprising the gel-delaying polymer and a crosslinker, as seen in similar art. By adding the gel-delaying polymer before the crosslinker, delays the gelation from days to weeks, allowing for deeper reservoir penetration.

[0061] The sequential injection can be followed by injection of fluids to displace the gelling composition or recover hydrocarbons. Alternatively, the carboxylate-containing polymer and gel-delaying polymer can be injected, followed by a fluid injection, before the crosslinker is injected.

[0062] In another embodiment, the gelant is injected as a single package complex of e.g. HPAM (AC24), temporarily carboxylated polymer such as poly(sodium aspartate) (PAsp) and/or polyvinyl alcohol succinate (PVAS), and metal ions (such as Cr(III)), as shown in FIG. 2. When the metal ion, e.g. Cr(III) is added into the mixture of HPAM and PAsp or PVAS, it will form complexes with the carboxyl groups of both HPAM and PAsp or PVAS, which leads to a single package of HPAM, PAsp and/or PVAS, Cr(III) complexes that can be injected. When settled into the reservoir, removal of carboxyl groups of PAsp or PVAS, triggered by hydrolysis or heat, will release the Cr(III), resulting in the HPAM forming a gel with Cr(III).

[0063] Molar ratios of COO.sup.− from PVAS or PAsp to metal ion range from 2:1, 4:1, 6:1, 10:1, 12:1; 16:1 and 20:1. Molar ratios of 6:1 to 12:1 are most preferred.

[0064] This composition of HPAM, PAsp/PVAS, Cr(III) complex (gelant fluid) can move forward as a single package in underground reservoir, thus minimizing or avoiding separation occurrence during delivery in underground reservoir. Experiments are still being conducted to determine if the package can chromatically separate downhole.

[0065] The polymer used to delay the gelation can be made from monomers selected from the group of vinyl, allyl, styrene, and acrylamide monomers and their derivatives, or any polysaccharide, conjugated with a di-carboxylate or having naturally appended carboxylate groups. Any di-carboxylate (or tricarboxylate) can be used, including citrate, succinate, aspartate, glutamate, malate, oxalate, malonate, glutarate, adipate, pimelate, and the like, or a derivative thereof.

[0066] In some embodiments, the gel-delaying polymer is a polymer or copolymer of citrate, succinate, aspartate, glutamate, malate, oxalate, malonate, glutarate, adipate, pimelate, carbonate, and the like, or derivatives thereof.

[0067] In some preferred embodiments, the gel-delaying polymer comprises polyvinyl alcohol (PVA) succinate, N-hydroxylmethyl acrylamide (NHMA) succinate, allyl alcohol succinate and allylamine succinate, PVA malate, NHMA malate, allyl alcohol malate or allylamine malate. In other embodiments, the polymer is polyaspartate or polyglutamate, or the like.

[0068] The crosslinker is any multivalent metal ion whose presentation needs be delayed, and for reservoir use and tertiary crosslinking. These include chromium, zirconium, iron, aluminum, and titanium ions. In some preferred embodiments, the multivalent metal ion is Cr(III).

[0069] Any carboxylate-containing polymer can be used in the injection, provided such polymer can be crosslinked with the metal ion. Such polymers include, e.g., partially hydrolyzed polyacrylamide, copolymers of N-vinyl-2-pyrrolidone and sodium acrylate, tetrapolymers of sodium-2-acrylamido-2-methylpropanesulfonate, acrylamide and N-vinyl-2-pyrrolidone and sodium acrylate; copolymers of sodium-2-acrylamido-2-methylpropanesulfonate and sodium acrylate; and combinations thereof.

[0070] In some embodiments, the carboxylate-containing polymer is HPAM or B29.

[0071] An improved method of sweeping a reservoir is also provided herein, wherein an injection fluid is injected into a reservoir to mobilize and produce oil, the improvement comprising injecting, in order, a carboxylate-containing polymer, at least one gel-delaying polymer and a crosslinker plus a fluid into a reservoir, aging said carboxylate polymer, at least one gel-delaying polymer, crosslinker and fluid to increase its viscosity, injecting additional injection fluid into said reservoir to mobilize oil, and producing said oil. The aging time can be varied, as described herein, to allow compete penetration of the reservoir.

[0072] Another improved method of sweeping a reservoir is also provided herein, wherein an injection fluid is injected into a reservoir to mobilize and produce oil, the improvement comprising injecting, in order, a carboxylate-containing polymer, at least one gel-delaying polymer and a crosslinker plus a fluid into an in-line mixer, mixing to form a complex, injecting said complex into the reservoir followed by an optional fluid injection to displace the complex, aging said complex and fluid to increase its viscosity, injecting additional injection fluid into said reservoir to mobilize oil, and producing said oil.

[0073] Another embodiment is a method of improving sweep efficiency of a fluid flood of a reservoir, said method comprising sequentially injecting the compositions herein described (plus polymer and fluid as needed) into a reservoir; aging the composition, e.g., 30-40 days or as needed (depending on reservoir temperature), to increase its viscosity; injecting an injection fluid into said reservoir to mobilize the oil; and producing said mobilized oil.

[0074] Another yet embodiment is a method of improving sweep efficiency of a fluid flood of a reservoir, said method comprising injecting a complex formed by a carboxylate-containing polymer, a gel-delaying polymer, and a crosslinker herein described (plus polymer and fluid as needed) into a reservoir; aging the composition, e.g., 30-40 days or as needed (depending on reservoir temperature), to increase its viscosity; injecting an injection fluid into said reservoir to mobilize the oil; and producing said mobilized oil.

[0075] The following experiments were performed to monitor gelling times for different compositions for use in deep oil-bearing formations. The gels described below utilized either Synthetic Brine A, listed in Table 1, or Synthetic Brine B, listed in Table 2.

TABLE-US-00002 TABLE 1 Composition of Synthetic Brine A Component Concentration, g/kg NaCl 22.982 KCl 0.151 CaCl.sub.2•2H.sub.2O 0.253 MgCl.sub.2•6H.sub.2O 1.071 NaHCO.sub.3 2.706 Na.sub.2SO.sub.4 0.145 Water To 1000 g

TABLE-US-00003 TABLE 2 Composition of Synthetic Brine B Component Concentration, g/kg NaCl 18.420 KCl 0.424 CaCl.sub.2•2H.sub.2O 0.550 MgCl.sub.2•6H.sub.2O 0.586 SrCl.sub.2•6H.sub.2O 0.061 NaHCO.sub.3 3.167 Na.sub.2SO.sub.4 0.163 Water To 1000 g

[0076] Several gelation tests were performed on the various gel made herein to demonstrate the suitability of the injection order with delayed gelation times. Brookfield Digital Viscometer Model LVDV-II+PCP was used to monitor the viscosity changes of gelant and control solutions and determine the gel time of the gelant solutions. The gelation process was monitored as a function of time starting from the point of visual homogeneous dispersion. The gelation time was defined as the time when the viscosity of the gel solution increases abruptly to a value greater than 1000 cP (100% scales) at a shear rate of 2.25 s.sup.−1. The temperature of the viscometer was controlled at the stated temperatures during the measurements.

[0077] GELATION OF AC24, PAsp AND CrCl.sub.3

[0078] A solution of Alcomer® 24 (AC24), the HPAM source, containing PAsp was prepared through mixing AC24 and PAsp, followed by addition of CrCl.sub.3, in Synthetic Brine A while stirring.

[0079] In an oxygen-free glove box, 75.00 g of 1% of AC24 in Synthetic Brine A was mixed with 7.73 g of a PAsp solution ([PAsp]=25.75 mg/g, pH=7.88 adjusted by NaOH and HCl) in 65.30 g of deoxygenated Synthetic Brine A with stirring.) 1.97 g of a CrCl.sub.3 solution ([Cr(III)]=7627 ppm) was added into the mixture of AC24 and PAsp while stirring to obtain a final AC24 concentration of 0.5%; final Cr(III) concentration of 100 ppm; and final molar ratio of COO— of PAsp to Cr(III) of 6:1.

[0080] The initial viscosity was recorded before the solution was divided into 6 ml vials and incubated at 120, 100 and 85° C. The viscosities of the samples were monitored as a function of time.

[0081] The gelation results are shown in FIG. 3. As this figure shows, the mixture of AC24, PAsp, and CrCl.sub.3 gelled within 2, and 5 days at 120 and 100, respectively. However, at 85° C., the gelation was delayed by 35 days. While 85° C. is the target temperature for the analysis, this increasing delay in time of gelation is expected for temperatures lower than 85° C. because the amide bond hydrolysis of PAsp is very slow at low temperature, such as 65° C.

[0082] GELATION OF B29, PAsp AND CrCl.sub.3

[0083] In addition to HPAM, the delay gelation was expected to occur in a similar polymer B29.

[0084] A sample of B29 (an expandable microparticle containing 95 mole percent acrylamide and 5 mole percent sodium acrylate, see e.g., US20140196894) in Synthetic Brine B was first prepared followed with addition of PAsp. CrCl.sub.3 in Synthetic Brine B was then added to this mixture. The details of this gelation experiment are described below:

[0085] In an oxygen-free glove box, 2.50 g of 30% B29 was added into 137.09 g deoxygenated Synthetic Brine B with 1.25 g of 30% of an inverting surfactant while stirring. 7.01 g of PAsp solution ([PAsp]=28.03 mg/g) was added to the stirring mixture. Finally, 2.06 g CrCl.sub.3 solution ([Cr(III)]=7284 ppm) was added into the above mixture of B29 and PAsp while stirring. Final B29 concentration was 0.5%; final Cr(III) concentration was 100 ppm; and final molar ratio of COO.sup.− of PAsp to Cr(III) was 6:1.

[0086] As with the HPAM example above, the initial viscosity was recorded before the solution was divided into 6 ml vials and incubated at 120, 100 and 85° C. The viscosities of the samples were monitored as a function of time.

[0087] The results are shown in FIG. 4. As this figure shows, the mixture of B29, PAsp, and CrCl.sub.3 complex gelled within 1, 8 and 33 days at 120, 100 and 85° C., respectively. Again, much longer delay in gelation was observed at 85° C.

[0088] B29 is largely the same as HPAM once it is popped, but its degree of hydrolysis is a bit lower (5%), thus it gels a little slower. However, both HPAM and B29 gelled in about the same time at identical temperatures.

[0089] GELATION OF AC24, PVAS AND CrCl.sub.3

[0090] Gels using PVAS in place of PAsp were also prepared to observe the differences in delay gelling.

[0091] A representative single package complex, herein referred to as AC24, PVAS, Cr(III), was prepared through mixing AC24 and PVAS with Cr(III) as CrCl.sub.3 in Synthetic Brine A while stirring. In more detail:

[0092] A stock PVAS solution was prepared through the reaction of poly(vinyl alcohol, Mw 25k, 88 mol % degree of hydrolysis) with succinic anhydride using triethylamine as catalyst in N-methyl-2-pyrrolidone as solvent according to the procedure reported in the literature..sup.(20)

##STR00001##

[0093] Stock solutions of PVAS and CrCl.sub.3 were prepared in RO water. The concentration of the PVAS stock solution was 66.17 mg/g and the concentration of the Cr(III) was 7841 ppm.

[0094] In an oxygen-free glove box, 25.00 g of 1% of AC24 was stirred into Synthetic Brine A. 2.73 g of the PVAS stock solution in 21.64 g deoxygenated Synthetic Brine A was added to the AC24 and stirred. 0.64 g of the CrCl.sub.3 stock solution was added to the above mixture of AC24 and PVAS while stirring. Final AC24 concentration was 0.5%; final Cr(III) was 100 ppm; final molar ratio of COOH of PVAS to Cr(III) was 12:1.

[0095] The initial viscosity was recorded before the solution was divided into 6 ml vials and incubated at 85 and 65° C. The viscosities of the samples were monitored as a function of time.

[0096] The results are shown in FIG. 5. As this figure shows, the single package of AC24, PVAS, CrCl.sub.3 complex gelled within 10 and 121 days at 85 and 65° C., respectively.

[0097] The difference in the experimental target values of the PVAS and PAsp system is due to the bonds being hydrolyzed. The PVAS system controls the release of metal ion crosslinkers by ester bond hydrolysis, which is faster than the amide bond hydrolysis of PAsp at the same temperature, e.g. 85° C. Thus, it is necessary to study the PVAS system at lower temperatures to slow the hydrolysis steps. As such, cooler temperatures are necessary to achieve larger delay times for the PVAS system.

[0098] GELATION OF B29, PVAS AND CrCl.sub.3

[0099] Gels using PVAS in place of PAsp with B29 were also prepared to observe the differences in delay gelation time.

[0100] In an oxygen-free glove box, 1.67 g of 30% B29 was inverted into 90.76 g of deoxygenated Synthetic Brine A with 0.83 g of an inverting surfactant while being stirred. Then, 5.46 g of the PVAS solution (66.17 mg/g) was stirred into the B29 solution. Finally, 1.28 g of the CrCl.sub.3 stock solution (7841 ppm) was added the above mixture of B29 and PVAS while stirring. Final B29 concentration was 0.5%; final Cr(III) was 100 ppm; final molar ratio of COO.sup.− of PVAS to Cr(III) is 12:1.

[0101] The initial viscosity was recorded before the solution was divided into 6 ml vials and incubated at 85 and 65° C. The viscosities of the samples were monitored as a function of time.

[0102] The results are shown in FIG. 6. As this figure shows, single package of B29, PVAS, CrCl.sub.3 complex gelled within 10 and 93 days at 85 and 65° C., respectively.

[0103] The present invention is exemplified with respect to the above examples and figures, however, this is exemplary only, and the invention can be broadly applied to many polymers systems used to block thief zones in hydrocarbon recovery techniques. The above examples are intended to be illustrative only, and not unduly limit the scope of the appended claims.

[0104] The following references are incorporated by reference in their entirety for all purposes.

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