partially hydrolyzed polyvinyl alcohol or as polyvinyl alcohol polyvinyl acetate copolymer an example is obtained from synthomer limited harlow essex united kingdom under the trade name alcotex wd200 this material is an aqueous solution containing approximately 20 of an approximately 43 hydrolyzed polyvinyl acetate having an average molecular weight of about 25 000 for shortening of shear recovery time suitable partially hydrolyzed polyvinyl acetate phpva may be from about 10 to about 95 hydrolyzed and have a molecular weight of from about 500 to about 100 000 000 for increasing fluid system rheology suitable phpva is from about 30 to about 88 hydrolyzed and has a molecular weight of from about 5000 to about 1 000 000 000 other esters of polyvinyl alcohol may be used for example c 2 to c 5 esters i e the partially hydrolyzed ethyl to pentyl esters of polyvinyl alcohol these materials were described in u s patent application publication no 2006 0128598 assigned to the same assignee as the present invention and hereby incorporated in its entirety other suitable amphiphilic polymers include partially hydrolyzed polyacrylates or partially hydrolyzed polymethacrylates or the like for example but not limited to partially hydrolyzed polymethyl acrylate partially hydrolyzed polyethyl acrylate partially hydrolyzed polybutyl acrylate partially hydrolyzed polymethyl methacrylate and mixtures of these polymers preparation and use mixing storing pumping etc of the improved ves fluid systems of the invention are the same as for such fluids without the rheology enhancers for example the order of mixing is.