Patent ID: 6020289
Filing Date: 2000-02-01
Classification: C09K

Abstract:
A process of drilling a wellbore in shale-containing rock in which material is removed from the rock and flushed by an aqueous drilling fluid to the surface of the wellbore, in which the aqueous drilling fluid contains a dissolved polymer formed from ethylenically unsaturated monomer or monomer blend, characterized in that the monomer or monomer blend consists essentially of(a) from 50 to 100 mol % monomers of the formula (I) ##STR5## wherein R.sup.1 is selected from H and C.sub.1 to C.sub.3 alkyl groupsR.sup.2 is selected from C.sub.1 to C.sub.3 alkyl groups, --C(CH.sub.3).sub.2 CH.sub.2 COCH.sub.3, --CH.dbd.CH.sub.2 and --C(CH.sub.3).dbd.CH.sub.2R.sup.3 is selected from H, C.sub.1 to C.sub.3 alkyl groups, --CH.dbd.CH.sub.2 and --CH.sub.2 .dbd.C(CH.sub.3)--wherein when R.sup.3 is H or C.sub.1 to C.sub.3 alkyl groups, then R.sup.1 is H and R.sup.2 is --CH.dbd.CH.sub.2 or --C(CH.sub.3).dbd.CH.sub.2and when R.sup.2 is --C(CH.sub.3).sub.2 CH.sub.2 COCH.sub.3 the R.sub.1 is H(b) 0 to 50 mol % other ethylenically unsaturated non-ionic monomers selected from the group consisting of acrylamide, methacrylamide, vinyl acetate and hydroxy-ethyl acrylate andwherein the monomer or monomer blend contains substantially no ionic ethylenically unsaturated monomers and the polymer has a weight average molecular weight of 200,000 or less.