Experimental investigation on water removal and gas flow during drainage process in tight rocks

Abstract

High performance water removal plays a significant role in restoring the gas production when water invasion happens to tight gas reservoirs. In this paper, core samples with the air permeability in range of 0.01–1 mD were selected to investigate water removal behavior in tight gas reservoirs. Meanwhile, the gas flow capability during the process of water removal was discussed. The water desaturation curves generally experienced two stages of water removal in a drainage process: a fast water decline stage induced by immiscible displacement, followed by a long period of slow water saturation reduction stage via the gas flow-through drying. It pointed out that the immiscible displacement mainly affects water removal during the drainage process in which period continuous gas flow channel was built. Once the generation of continuous gas flow channel was accomplished during the immiscible displacement stage, a proper increase of displacement pressure difference can efficiently enhance the gas flow-through drying rate. Normally, it was easy for high permeable tight core sample to experience a short immiscible displacement dominant stage and step into gas flow-through drying dominant stage afterwards. Besides, it was found that the enlargement in water invasion depth will weaken gas flow capacity from water removal. These findings help in understanding the physical process of water removal in tight gas reservoirs, as well as designing a better performance of water removal in a tight gas flied.