a water permeability correction process , and composition therefor , to improve the sweep efficiency of waterflooding which involves the sequential injection of an optical aqueous preflush slug to adjust connate water salinity , an aqueous sequestered polyvalent metal cation , such as chromium , wherein the sequestering anion is bactericidal , such as propionate , a gelable polymeric viscosifier , such as polyacrylamide , and , preferably , an aqueous drive fluid .