METHOD OF CARRYING OUT A WELLBORE OPERATION

摘要

A drilling mud comprising a base fluid in the form of a water-in-oil emulsion comprising droplets of a brine phase dispersed in a continuous oil phase wherein the brine phase has a dissolved salt concentration of at least 2.5 weight % and the emulsion is stabilized with (i) a first polymeric emulsifier that is a block or graft copolymer of the general formula (A-COO)mB, wherein m is an integer of at least 2, A is a polymeric component having a molecular weight of at least 500 and is the residue of an oil-soluble complex mono-carboxylic acid and (ii) a second polymeric emulsifier that is a graft copolymer of a polyvinylpyrrolidone polymer and an alpha olefin selected from the group consisting of C14 to C20 alphaolefins and mixtures thereof and wherein structural units derived from vinylpyrrolidone are present in the graft copolymer in an amount in the range of 40 to 50 mole %.