Dehydration and Permeability of Gels Used in In-Situ Permeability Modification Treatments

Abstract

Abstract Aqueous gels placed in oil reservoirs to reduce the permeability to water can undergo partial dehydration in which part of the water contained in the gel is expelled under an imposed pressure gradient. This paper describes a study of the dehydration behavior of a polyacrylamide-chroium acetate gel in which both oil and water were used to impose a pressure gradient on bulk gels. Bulk gels were formed in cylindrical cells. The gel was held in place by a 10-micron Teflon frit at the exit end of the cell. Brine or mineral oil at a fixed pressure was placed at the other end of the gel. Flow rates of brine exiting the frit were measured. Pressure gradients between 12 and 1130 psi/ft were imposed. Dehydration of the gel occurred with both oil and water as the dehydrating fluids. Dehydration was characterized by the formation of a finger of the dehydrating fluid near the central axis of gel and the formation of a filter cake on the exit frit. Mass balances revealed that the amount of polymer in the filter cake was very close to the amount of polymer in the finger volume based on the initial polymer concentration in the gel. Dehydration reduced the gel volumes by 50 to 70 %. The rate and final percent of dehydration was greater when oil was used as the dehydrating fluid. Permeabilities of the filter cake and the non-dehydrated bulk gel were determined to be on the order of 1 μd for the filter cake and in the range of 0.3 to 0.8 md for the bulk gel.