Experimental Study on Mechanism of Water-Alternating-Gas Injection in thick Sandstone Reservoir

For the thick sandstone reservoir, due to gravity differentiation, water drive mainly uses bottom oil of while gas drives along top reservoir. Water-alternating (WAG) injection can effectively combine advantages flooding and injection, so that work in synergy, thus further expanding swept volume enhancing recovery. Over past half century, technology has been successfully applied more than 60 oilfields worldwide, but its mechanism remains be studied. In this paper, a total three tests were conducted through conventional water-flooding (WF), followed by WAG sand-packed 2d-model. These experimental processes are recorded video with time saturation distribution each phase porous media observed，migration law is studied, displacement analyzed. The results show capillary force have great influence on process alternation, increasing overall gas; water/gas alternating highest recovery factor (RF) 75.45% test 3, comparison (70.85% 2) (66.7%in 1); Increase cycles tends reduce residual saturation.