Disproportionate Permeability Reduction With Pore-Filling Gels

Summary An idealistic goal of water-shutoff technology is that of identifying materials that can be injected into any production well (without zone isolation) and that will substantially reduce the water productivity without significantly impairing hydrocarbon productivity. Although many polymers and gels reduce permeability to water more than to oil or gas, several factors currently limit widespread field applications of this disproportionate permeability-reduction property. Chromium (III)-acetate-hydrolyzed polyacrylamide [Cr(III)-acetate-HPAM] pore-filling gels were investigated to overcome these limitations. For porous media with pregel kw(at Sor) ranging from 120 to 6,500 md, one pore-filling gel consistently reduced kw to about 0.24 md (ranging from 0.12 to 0.37 md). In contrast, in Berea sandstone with kw (at Sor) ranging from 222 to 363 md, a commercially available relative- permeability modifier (i.e., a suspension of gel particles) exhibited a much wider range of post-polymer kw values—from 0.75 to 202 md. Thus, pore-filling gels can provide greater reliability and behavior that is insensitive to the initial rock permeability. With sufficient oil throughput, Cr(III)-acetate-HPAM porefilling gels dehydrate, thus increasing permeability to oil. Several gel formulations provided water residual-resistance factors (permeability-reduction factors) greater than 2,000 and ultimate oil residual-resistance factors (Frro) values of 2 or less. These results provide hope that our current approach will identify gels that can treat either fractured or unfractured production wells successfully and reliably without zone isolation. Significant oil throughput was required to achieve low Frro values, suggesting that gelant penetration into porous rock must be small (a few feet or less) for existing Cr(III)-acetate-HPAM pore-filling gels to provide effective disproportionate permeability reduction.