Process for enhanced delayed in situ gelation of chromium polyacrylamide

Abstract

The present invention is a process for selectively plugging high permeability zones of a subterranean hydrocarbon-bearing formation by enhancing the delay associated with the in situ formation of a polymer gel. The process comprises predetermining a gelation delay time based on a formation's temperature, permeability and porosity, the distance from the well bore a region to be plugged is located, and a volumetric rate of gelation fluid injection. A gelation solution is then prepared comprising polyacrylamide a polyvalent metal carboxylate crosslinking agent, a gelation delaying agent and a buffer with a pKa of about 3.5 to about 6.8. Gelation delays are achieved by selecting the polyacrylamide concentration, delaying agent concentration and type, and buffer concentration and type, for given formation conditions. Delay times can range from several hours to several weeks at formation temperatures near 176.degree. F. (80.degree. C.) and from several hours to about one day at formation temperatures above about 219.degree. F. (104.degree. C.). The prepared solution is then injected into the formation via a well bore and allowed to gel. The gel selectively plugs high permeability zones within a subterranean hydrocarbon-bearing formation, at temperatures and distances from the well formerly unobtainable, resulting in improved vertical or areal conformance of injected fluids and improved oil production.