Permeability Reduction by Treatment With KUSP1 Biopolymer

Abstract

Summary The application of KUSP1 biopolymer for use in permeability reduction treatments of oil reservoirs was investigated. KUSP1 is a nontoxic polysaccharide that is produced by a bacterium. Alkaline solutions of KUSP1 have low viscosities and can be gelled by different methods. Three methods were examined to gel KUSP1 in porous media. Two of the methods are based on the reduction of pH of alkaline KUSP1 solutions. KUSP1 is soluble in alkali but forms a gel when the pH is lowered to values below 10.8. The first method employed the hydrolysis of an ester to reduce pH and trigger gelation. Gel times on the order of days were observed for KUSP1 solutions that contained the monoethylphthalate (MEP) ester. The performance of the KUSP1-MEP system in treatments of sandpacks, Berea cores, and carbonate field plugs was studied at 25°C. Brine permeabilities were reduced by factors that ranged from 75 to 4,500. Permeability reduction by treatments with the KUSP1-MEP system was stable to brine flow for periods of up to six months. The second method to gel alkaline KUSP1 solutions was based on the chemical interactions with rock material. It was found that interactions with Berea sandstone, Baker dolomite, silica sand-packs, and field core plugs were insufficient to reduce the pH of alkaline KUSP1 solutions to values required for gelation. Alkaline KUSP1 solutions were gelled by the addition of boric acid in the third method. Bulk gelation studies conducted at 25, 45, and 65°C showed that gel times could be regulated up to several days by selection of pH and boric acid concentrations. The gels were more rigid than those produced by pH-reduction methods, indicating a different gelation mechanism. Syneresis was observed and was more pronounced at lower pH values and higher temperatures. The KUSP1-boric acid system reduced brine permeabilities in sandpacks and Berea cores (25, 45°C) by factors that ranged from 50 to 3,300.