Low pH crosslinking of polymers
The invention is directed to polymers that self-crosslink at acidic pH or can be crosslinked by phenolic agents in brine. Such polymers have lower viscosity and can be pumped deep into reservoirs, where they will cross link in situ, thus increasing their viscosity and/or form a gel and blocking thief zones. Methods of making and using such polymers are also provided.
1. A composition comprising i) a polymer with one or more acrylamide-based monomers in the repeat unit, wherein at least one monomer has pendant hydroxyl groups, ii) a fluid, and iii) a phenolic crosslinker, wherein said polymer has a first viscosity at pH 8 and a second higher viscosity or forms a gel when aged at a pH less than 5, wherein said polymer is a terpolymer.
2. The composition of claim 1 , wherein said at least one monomer having a pendant hydroxyl group is selected from a group consisting of N-hydroxyethylacrylamide, N-(2-Hydroxypropyl)methacrylamide and N-hydroxymethylacrylamide.
3. The composition of claim 1 , wherein said terpolymer comprises an acrylamide monomer and one monomer having a pendant hydroxyl group, wherein said one monomer having a pendant hydroxyl group is selected from a group consisting of N-hydroxyethylacrylamide, N-(2-Hydroxypropyl)methacrylamide and N-hydroxymethylacrylamide.
4. The composition of claim 3 , wherein the third monomer in said terpolymer is sodium 2-acrylamido-2-methylpropane sulfonate.
5. The composition of claim 1 , wherein said terpolymer is poly[acrylamide-(sodium 2-acrylamido-2-methylpropane sulfonate)-N-hydroxymethylacrylamide].
6. The composition of claim 1 , wherein said phenolic crosslinker is chosen from a group containing phenol, catechin, resorcinol, phenyl acetate, salicyl alcohol, aspirin, m-cresol, phloroglucinol, quercetin, gallocatechin, naringenin, eriodictyol, afzelechin and epimers thereof.
7. The composition of claim 1 , wherein said fluid comprises CO 2 .
8. A composition comprising poly[acrylamide-(sodium 2-acrylamido-2-methylpropane sulfonate)-N-hydroxymethylacrylamide], water or brine, and a phenolic crosslinker.
9. The composition of claim 8 , wherein said phenolic crosslinker is selected from a group consisting of phenol, catechin, resorcinol, m-cresol, phenyl acetate, salcyl alcohol, aspirin, phloroglucinol, quercetin, gallocatechin, naringenin, eriodictyol, afzelechin and epimers thereof.
10. A composition comprising poly[acrylamide-(sodium 2-acrylamido-2-methylpropane sulfonate)-N-hydroxymethylacrylamide], water or brine, and a phenolic crosslinker selected from phenol, catechin, resorcinol, m-cresol, phenyl acetate, salcyl alcohol, aspirin, phloroglucinol, quercetin, gallocatechin, naringenin, eriodictyol, afzelechin and epimers or combinations thereof, wherein said composition has a first viscosity at pH 8 and a second higher viscosity when aged at a pH less than 5.
11. An improved method of CO 2 flooding, wherein CO 2 is injected into a reservoir to mobilize and produce oil, the improvement comprising injecting the composition of claim 1 into a reservoir, aging said composition to increase its viscosity or form a gel, injecting CO 2 into said reservoir to mobilize oil, and producing said mobilized oil.
12. An improved method of Water-Alternating-Gas enhanced oil recovery, wherein alternate slugs of water or brine and slugs of CO 2 are injected into a reservoir to mobilize and produce oil, the improvement comprising injecting slugs of CO 2 into said reservoir to mobilize oil, and producing said oil until production levels drop, then injecting the composition of claim 1 into said reservoir, aging said composition in situ to increase its viscosity or form a gel and further injecting alternate slugs of water or brine and slugs of CO 2 into said reservoir to further mobilize oil, and producing said further mobilized oil.