The influence of water saturation and confining pressure to gas porosity and permeability of sandstone

Abstract

Understanding of gas porosity and permeability is important in gas storage, recovery and nuclear waste disposal. In this paper, we focus on the gas porosity and permeability variation of sandstone at different water saturation in loading–unloading cycle. Through an improved method, we prepared the samples with water saturation level from 0 to 81%. The test results suggest that gas effective permeability and porosity are sensitive to confining pressure. This is particularly true in low pressure from 1 to 10 MPa. There is a significant difference between loading and unloading process. This is caused by irreversible deformation of pores and microcracks. The existence of water inside samples leads to a change of permeability on the order of magnitudes from 10−13 to 10−15 m2. Water saturation also influences the sandstone porosity significantly. We observed that the gas relative porosity almost decreases linearly with the increase of water saturation. A simple power law is modified to describe the relationship between gas effective permeability and porosity.