Weak gel system for chemical enhanced oil recovery

1. A method of increasing the sweep efficiency of a fluid flood of a subterranean hydrocarbon-bearing formation to enhance hydrocarbon recovery from the formation, the method comprising:

introducing either a water soluble acrylamide polymer and a non-metallic organic crosslinking agent, or a crosslinkable acrylamide polymer, into an injection fluid entering a wellbore or the formation to form a crosslinked polymer in a high permeability zone existing within the formation;

discontinuing hydrocarbon production from the formation being treated for a time period sufficient to allow the viscosity of the crosslinked polymer within the high permeability zone to increase so that the crosslinked polymer remains fixed within the high permeability zone to divert fluid flow into unswept zones of the formation;

after the discontinuation step, introducing injection fluid into the formation being treated to flood the formation, mobilize the hydrocarbon and form a flood fluid containing a mobilized hydrocarbon; and

removing the flood fluid containing the mobilized hydrocarbon from the well as a produced fluid,

wherein the non-metallic organic crosslinking agent comprises a polymeric polyamine which is either (i) a reaction product of a polymerization mixture comprised of at least one monomer of Formula II or a salt thereof; or (ii) comprised of at least one structural unit of Formula IIA, wherein Formulae II and IIA have the following structures:

wherein:

R 1 is hydrogen, a protecting group, or alkyl; and

R 2 , R 3 , R 4 , R 5 , R 6 and R 7 are each independently hydrogen, alkyl, or alkoxylalkyl; and

the crosslinkable acrylamide polymer comprising a reaction product of a polymerization mixture comprised of at least one acrylamide monomer and at least one monomer of the Formula II or a salt thereof.

2. The method of claim 1 , wherein the water soluble acrylamide polymer and the non-metallic organic crosslinking agent are introduced into the injection fluid.

3. The method of claim 2 , wherein the water soluble acrylamide polymer and the non-metallic organic crosslinking agent are separately introduced into the injection fluid.

4. The method of claim 2 , wherein the water soluble acrylamide polymer has a molecular weight of from about 0.05 to about 25 megadaltons (“MDa”) or from about 5,000 Daltons to about 25 MDa.

5. The method of claim 4 , wherein the crosslinking agent has a molecular weight of from about 0.1 to about 1.5 MDa.

6. The method of claim 2 , wherein the weight ratio of the water soluble acrylamide polymer to the non-metallic organic crosslinking agent ranges from about 100:1 to about 1:100 or from about 2:1 to about 60:1.

7. The method of claim 2 , wherein the water soluble acrylamide polymer comprises polyacrylamide or partially hydrolyzed polyacrylamide containing up to about 40 mole percent degree of hydrolysis.

8. The method of claim 2 , wherein the water soluble acrylamide polymer comprises either: an anionic co-polymer of acrylamide and up to about 40 mole % of an acrylic acid; an anionic co-polymer of acrylamide and up to about 40 mole % of 2-acrylamido-2-methylpropane sulfonic acid (“AMPS”); an anionic terpolymer of acrylamide and up to about 40 mole % of a combination of acrylic acid and AMPS; a terpolymer of acrylamide and up to about 40 mole % of a combination of AMPS and N-vinylpyrrolidone (“NVP”); or a terpolymer of acrylamide and up to about 40 mole % of a combination of t-butyl-acrylate and NVP.

9. The method of claim 1 , wherein the water soluble acrylamide polymer concentration is from about 200 to about 2,000 ppm.

10. The method of claim 2 , wherein the water soluble acrylamide polymer concentration is greater than 2,000 ppm.

11. The method of claim 1 , wherein the non-metallic organic crosslinking agent is a polyamine comprising a homopolymer or copolymer of a dialkylamine.

12. The method of claim 11 , wherein either: the non-metallic organic crosslinking agent comprises a homopolymer of diallylamine.

13. The method of claim 1 , wherein the non-metallic organic crosslinking agent concentration is from about 5 to about 500 ppm.

14. The method of claim 2 , wherein during the enhanced hydrocarbon recovery operation, the water soluble acrylamide polymer and the non-metallic organic crosslinking agent are continuously added into the injection fluid entering the wellbore or the formation; the water soluble acrylamide polymer and the non-metallic organic crosslinking agent are intermittently added into the injection fluid entering the wellbore or the formation; the water soluble acrylamide polymer is intermittently added into the injection fluid entering the wellbore or the formation, and the non-metallic organic crosslinking agent is continuously added into the injection fluid entering the wellbore or the formation; or the non-metallic organic crosslinking agent is intermittently added into the injection fluid entering the wellbore or the formation, and the water soluble acrylamide polymer is continuously added into the injection fluid entering the wellbore or the formation.

15. The method of claim 1 , wherein the crosslinkable acrylamide polymer is introduced into the injection fluid.

16. The method of claim 15 , wherein the crosslinkable acrylamide polymer comprises the reaction product of the polymerization mixture comprised of the acrylamide monomer and diallylamine.

17. The method of claim 15 , wherein the crosslinkable acrylamide polymer is introduced into the injection fluid, and a water soluble acrylamide polymer is introduced into the injection fluid.

18. The method of claim 17 , wherein the water soluble acrylamide polymer and the crosslinkable acrylamide polymer are continuously added into the injection fluid entering the wellbore or the formation; the water soluble acrylamide polymer and the crosslinkable acrylamide polymer are intermittently added into the injection fluid entering the wellbore or the formation; the water soluble acrylamide polymer is intermittently added into the injection fluid entering the wellbore or the formation, and the crosslinkable acrylamide polymer is continuously added into the injection fluid entering the wellbore or the formation; or the crosslinkable acrylamide polymer is intermittently added into the injection fluid entering the wellbore or the formation, and the water soluble acrylamide polymer is continuously added into the injection fluid entering the wellbore or the formation.

19. The method of claim 1 , wherein either: the subterranean formation is an oil-bearing sandstone or carbonate reservoir; the produced fluid is treated to recover the hydrocarbon; or the injection fluid comprises seawater, aquifer water, produced water, or a surfactant.

20. The method of claim 1 , wherein viscosity of the flowable crosslinked polymer increases at increased temperature and fluid diversion conformance occurs wherein the flowable crosslinked polymer becomes non-flowable such that it remains fixed within a high permeability zone of the formation to divert fluid flow into unswept zones of the formation.

21. The method of claim 11 , wherein either: the non-metallic organic crosslinking agent comprises a copolymer of diallylamine with an acrylamide or an acrylic acid, or a terpolymer of diallylamine with an acrylamide and an acrylic acid; or the non-metallic organic crosslinking agent comprises a copolymer of diallylamine with AMPS or NVP, or a terpolymer of diallylamine with AMPS and NVP.