Method for controlling permeability of subterranean formations

Claim 2

In a well drilling method wherein a drilling fluid is injected into a borehole in the earth during the drilling of the borehole, the improvement which comprises injecting as the drilling fluid a fluid medium containing discrete spheroidal microgels of a water-swellable or water-swollen crosslinked polymer in an amount sufficient to reduce the loss of the drilling fluid via penetration of porous subterranean strata proximate to the borehole, said polymer being crosslinked with from about 5 to about 200 weight parts of copolymerizable polyethylenic monomer per million parts of total monomers of the polymer.

Claim 3

In an enhanced oil recovery method in which an aqueous drive fluid is injected through an injection well bore into a hydrocarbon-bearing nonfractured formation having hydrocarbon-deficient and hydrocarbon-rich zones to drive hydrocarbon from the formation to a recovery well, the improvement wherein an aqueous fluid medium containing discrete, spheroidal microgels of a water-swellable or water-swollen, crosslinked polymer of ethylenically unsaturated water-soluble monomer(s) is introduced through the injection well bore into the formation in an amount sufficient to reduce the aqueous fluid permeability of the porous formation, said polymer being crosslinked with from about 5 to about 200 weight parts of copolymerizable polyethylenic monomer per million parts of total monomers of the polymer and said microgels in at least a partially water-swollen state having diameters in the range from about 0.5 to about 200 micrometers, thereby restricting the passage of the drive fluid into hydrocarbon-deficient zones of the formation but not substantially impeding the passage of the drive fluid through hydrocarbon-rich zones of the formation.

Claim 4

In an enhanced oil recovery method in which an aqueous drive fluid is injected through an injection well bore into a hydrocarbon-bearing nonfractured formation having hydrocarbon-deficient and hydrocarbon-rich zones to drive hydrocarbon from the formation to a recovery well, the improvement wherein an aqueous fluid medium containing discrete, spheroidal microgels of a water-swellable or water-swollen, crosslinked polymer of ethylenically unsaturated water-soluble monomer(s) is introduced through the injection well bore into the formation in an amount sufficient to reduce the aqueous fluid permeability of the porous formation, said polymer being crosslinked with from about 5 to about 200 weight parts of copolymerizable polyethylenic monomer per million parts of total monomers of the polymer and said microgels in at least a partially water-swollen state having diameters in the range from about 0.5 to about 200 micrometers, thereby restricting the passage of the drive fluid into hydrocarbon-deficient zones of the formation but not substantially impeding the passage of the drive fluid through hydrocarbon-rich zones of the formation.

Claim 5

The improvement of claim 1 or claim 2 wherein the polymer is crosslinked with from about 5 to about 200 weight parts of copolymerizable N,N'-alkylidene-bis-(ethylenically unsaturated amide) per million parts of total monomers of the polymer.

Claim 6

The improvement of claim 3 wherein the polymer is a polymer of acrylamide.

Claim 7

The improvement of claim 3 wherein the N,N'-alkylidene-bis(ethylenically unsaturated amide) is N,N'-methylene-bis(acrylamide).

Claim 8

The improvement of claim 1 or 2 wherein the water-soluble monomer(s) is a mixture of acrylamide and acrylic acid and the polymer is crosslinked with from about 10 to about 100 weight parts of N,N'-methylene-bis(acrylamide).