Influencing mechanism and modelling study of pore pressure and temperature on shale permeability

A series of gas flow tests using He and CO2 are conducted on shale samples in triaxial flow equipment for rock to investigate the influencing mechanisms of pore pressure and temperature on permeability. The experimental re- sults show that non-sorbing He permeability increases with pore pressure. However,the permeability evolution of sor- bing CO2 first decreases and then recovers as pore pressure increases. Then,a theoretical model is proposed to predict the permeability change induced by effective stress,matrix swelling and gas slippage. Furthermore,the validation of the proposed model is conducted by fitting the experimental results from this paper. The flow tests under variable tempera- tures demonstrate that the shale permeability declines first at low temperature,and then increases at high temperature. It is observed that temperature has a stronger impact on permeability under lower confining pressure. With the increase of temperature,the slippage effects on the permeability become stronger. The effect of temperature on gas permeability is altered as a combined action of the thermal expansion of grains,gas slippage,the thermal motion of gas molecular and the matrix swelling induced by adsorption. At last a theoretical model is built with the consideration of temperature effects,and is validated by comparing the experimental results and analytic results,which gives satisfactory agreements between each other.