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 for acid diversion in acidizing a reservoir, said composition being a solution comprising a polymer plus a phenolic crosslinker plus a fluid;
a) wherein said polymer comprises one or more acrylamide-based monomer(s) at 0.2-20 mole percent;
b) wherein at least one of said acrylamide-based monomer(s) has pendant hydroxyl groups ranging from 0.1-99 mole percent;
c) wherein said composition has a first viscosity at pH 8 and forms a gel when aged for a period of time at pH less than 5, and
d) wherein said phenolic crosslinker is at 50-5000 ppm (w/w) in said solution.
2. The composition of claim 1 , wherein the concentration of said polymer in said solution is 0.4-10%.
3. The composition of claim 1 , wherein the phenolic crosslinker is 100-1000 ppm (w/w) in said solution.
4. The composition of claim 1 , wherein said at least one of said acrylamide-based monomer(s) having a pendant hydroxyl group is chosen from a group consisting of N-hydroxyethylacrylamide, N-(2-Hydroxypropyl)methacrylamide, and N-hydroxymethylacrylamide.
5. The composition of claim 1 , wherein said period of time is 30 days.
6. The composition of claim 1 , wherein said period of time is 60 days.
7. The composition of claim 5 , wherein said phenolic crosslinker is chosen from a group consisting of phenol, catechin, resorcinol, m-cresol, phenyl acetate, salicyl alcohol, aspirin, phloroglucinol, quercetin, gallocatechin, naringenin, eriodictyol, afzelechin, and epimers thereof.
8. The composition of claim 6 , wherein the said phenolic crosslinker is chosen from a group consisting of phenol, catechin, resorcinol, m-cresol, phenyl acetate, salicyl alcohol, aspirin, phloroglucinol, quercetin, gallocatechin, naringenin, eriodictyol, afzelechin and epimers thereof.
9. The composition of claim 1 , wherein said at least one of said acrylamide-based monomer(s) having a pendant hydroxyl group is chosen from a group consisting of N-hydroxyethylacrylamide, N-(2-Hydroxypropyl)methacrylamide and N-hydroxymethylacrylamide, and said phenolic crosslinker is chosen from a group consisting of phenol, catechin, resorcinol, m-cresol, phenyl acetate, salicyl alcohol, aspirin, phloroglucinol, quercetin, gallocatechin, naringenin, eriodictyol, afzelechin and epimers thereof.
10. A method of acid diversion in acidizing a reservoir, said method comprising:
a) injecting the composition of claim 1 into a reservoir;
b) aging said composition until it gels and thereby will divert acid; and
c) acidizing said reservoir.
11. The method of claim 10 , wherein the composition is aged for at least 30 days.
12. The method of claim 10 , wherein the composition is aged for at least 60 days.
13. The method of claim 10 , further comprising producing oil from said reservoir.