Experimental study on permeability in tight porous media considering gas adsorption and slippage effect

Permeability is an important parameter that helps understand the gas mass transport behavior in tight porous media. However, measuring the permeability of tight porous media accurately is an arduous task. Gas flow differs from liquid flow in regards to high compressibility, slippage effect, and sometimes adsorption. Slippage effect can be significant when the pressure is low or the pore diameter is small. Increasing pressure eliminates the slippage effect; however, high pressure is not always achievable under lab or field production conditions. The measurement of permeability during gas flow in a porous media is also greatly affected by the adsorption-induced surface diffusion process. In this study, a combined experimental-mathematical method for determining the permeability of tight porous media was developed. Steady-state measurements were conducted to obtain methane flux under different pressures for shale and tight reservoirs. The apparent permeability and permeability without slippage were calculated. Using the measured parameters, a mathematical model was derived to determine the intrinsic permeability, and the viability was tested with experimental results. This work provides an alternative approach to estimate the permeability of tight porous media during the gas mass transport process by considering both the slippage effect and gas surface adsorption. Parameters in the model can be easily measured through experiments for low pressures. Experimental verification shows that the error of permeability estimation can be decreased by approximately 10%.