CO.sub.2 -induced in-situ gelation of polymeric viscosifiers for permeability contrast correction

摘要

A water permeability contrast correction process to improve the sweep efficiency of waterflooding which involves the sequential injection of (1) an optional aqueous preflush slug to adjust connate water salinity, (2) an aqueous thickened slug comprising a sequestered polyvalent metal cation such as aluminum citrate and a gelable polymeric viscosifier such as polyacrylamide, (3) carbon dioxide to decrease the pH of the polymer slug which triggers the delayed in-situ gelation of said thickened slug to preferentially decrease water permeability in highly permeable thief zones, and (4) an aqueous drive fluid.