Study on seepage characteristics and stress sensitivity of sandstone under cyclic water intrusion based on CT scanning technique

The cyclic water intrusion and stresses lead to changes in the rock pores' microstructure, which affects the rock’s seepage characteristics. This study performs a three-dimensional reconstruction of the rock specimen using the Avizo software based on the results of multiple computed tomography (CT) tests conducted on sandstone subjected to varying numbers of cyclic water intrusions. In addition, a numerical model comprising pores and grain matrix is developed, based on which stress loading and seepage simulations are carried out. The results show that the mean outlet velocity, maximum seepage pressure, and permeability of the rock samples show an exponential increase with the number of cyclic water intrusions. Stress loading of the rock samples reveals that as the stress increases, the average exit velocity and permeability decrease. It is observed that the stress sensitivity index tends to increase and subsequently decrease with the number of water intrusion cycles at the same stress level when the stress sensitivity index is calculated under different water intrusion cycles. The relationship between effective stress, porosity, and stress sensitivity index is derived, and an effective linkage between permeability and macro-mechanical parameters considering stress sensitivity is achieved.