A method of shale inhibition comprises adding a two-phase polymer system
of a water soluble copolymer of vinyl pyrrolidone and dimethylaminopropyl
methacrylamide and in-situ formed water-insoluble particles of said
copolymer, or, alternatively, a water-soluble copolymer of methylvinyl
ether and maleic anhydride, into a drilling well fluid under aqueous,
high temperature, high salinity conditions.