Experimental investigation on liquid permeability of tight rocks under back pressure conditions

With the popularity of unconventional reservoirs having the remarkable features of extremely low permeability and low porosity, liquid permeability measurement of tight rocks from the unconventional reservoirs is facing severe challenges. At laboratory, it will require a high displacement pressure (which is the differential pressure between two pressure sensors during the measurement) gradient and a long testing time to measure liquid flow rate of tight rocks without a back pressure normally. In fact, reservoir fluid flow exists a back pressure and the production pressure gradient (simulated by displacement pressure gradient at laboratory) cannot be as high as it exerted in laboratory. To better simulate the reservoir liquid flow behavior and to investigate the effect of back pressure on liquid flow in tight rocks, we measured the liquid flow rate and studied the pressure transmission by exerting back pressure at the outlet of core samples during the experiment. The results showed that the liquid flow rate of tight rocks improved as a function of increasement in back pressure, and that it will shorten the testing time and reduce the desired displacement pressure to measure liquid permeability in tight rocks by exerting a back pressure. Based on our work, this paper aims to offer an effective method in liquid permeability measurement of tight rocks, and expect to provide an inslight into liquid flow behavior in tight rocks.