Experimental research on stress-dependent permeability and porosity of compact sandstone with different moisture saturations

Abstract

In this paper, compact sandstone with different moisture saturation from 0% to 73.60% was prepared. Subsequently, gas permeability and porosity of the prepared rock specimens under different pore pressure during confining pressure loading and unloading was measured. The experimental results indicate that, for rock specimen with moisture saturation 0%, 9.63%, 22.10%, 33.60%, and 42.30%, gas permeability rises with the increase of pore pressure due to Klinkenberg Effect, while for rock specimens with moisture saturation 54.36% and 73.60%, the opposite phenomenon was observed because the flow rate of gas has the dominant influences on the gas permeability than that of Klinkenberg Effect. The quadratic equation has better performance in describing the Klinkenberg Effect than that of Klinkenberg equation. Klinkenberg Effect enhances with the increase of moisture saturation and confining pressure, respectively, due to the decrease of equivalent pore radius for gas flow. With the rise of moisture saturation, the decreasing rate of intrinsic permeability under low moisture saturation is low than that under high moisture saturation. The intrinsic permeability of rock specimens with high moisture saturation is more sensitive to loading and unloading than that with low moisture saturation. The relationship between intrinsic permeability/porosity of rock specimens and confining pressure can be described correctly by adopting the exponential function model and power function model, respectively. Additionally, the gradual increase in moisture content in rock specimens revealed significant decrease on intrinsic permeability. This was attributed to clay swelling which contributed to blockage of seepage paths.