Experimental Study of Water Shut-Off by Wettability Alteration to Gas Wetness

Abstract

AbstractGas wells may suffer significant decline in gas production or even get killed because of the water invasion into production zones. Closing off the water producing zone may not be acceptable in many cases. In this study, the feasibility of reducing the water production in gas wells by changing the wettability of the gas zone from preferential water- to gas-wetness using fluorine carbon surfactant has been investigated experimentally. The basic mechanism was that the entry capillary pressure has to be overcome prior to water entering the gas zone. Naturally water can imbibe into gas zones spontaneously because the rock in gas zones is water wet, most probably. After the wettability alteration from water- to gas-wetness, water cannot enter into gas zones if the differential pressure is less than the entry capillary pressure and the water flux will be significantly reduced even if the differential pressure is greater than the entry capillary pressure. An artificially made, consolidated two-layer core model was used to conduct the study. The two layers had different permeability and the top layer was served as the gas zone and the bottom layer served as the bottom aquifer. The gas production was measured at different initial water saturations with and without wettability alteration from preferential water- to gas-wetness in gas zone. The experimental results showed that the water breakthrough time could be postponed and that the amount of water invaded into the gas zone could be reduced significantly by altering the wettability of the gas zone to gas wetness. The advantages of this approach to reducing water production were: 1) the permeability of the gas zone was not affected notably by the chemical treatment for wettability alteration; 2) the chemical treatment for wettability alteration had great longevity.