Permeability reduction by treatment with KUSP1 biopolymer

The application of KUSP1 biopolymer for use in permeability reduction treat ments of oil reservoirs was investigated. KUSP1 is a nontoxic polysaccharid e that is produced by a bacterium. Alkaline solutions of KUSP1 have low vis cosities and can be gelled by different methods. Three methods were examine d to gel KUSP1 in porous media. Two of the methods are based on the reducti on 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 trigg er gelation. Gel times on the order of days were observed for KUSP1 solutio ns that contained the monoethylphthalate (MEP) ester. The performance of th e KUSP1-MEP system in treatments of sandpacks, Berea cores, and carbonate f ield plugs was studied at 25 degreesC. 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 si x 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 sandpacks, and field core plugs were ins ufficient to reduce the pH of alkaline KUSP1 solutions to values required f or gelation. Alkaline KUSP1 solutions were gelled by the addition of boric acid in the t hird method. Bulk gelation studies conducted at 25, 45, and 65 degreesC sho wed 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 produce d by pH-reduction methods, indicating a different gelation mechanism. Syner esis was observed and was mon pronounced at lower pH values and higher temp eratures. The KUSP1-boric acid system reduced brine permeabilities in sandp acks and Berea cores (25, 45 degreesC) by factors that ranged from 50 to 3, 300.