Influence of CH4 adsorption diffusion and CH4-water two-phase flow on sealing efficiency of caprock in underground energy storage

Abstract

Underground natural gas energy storage (UNGNS) plays an important role in ensuring the reliability of the pipeline equipment and the stability of the energy market. In this paper, a mathematical model of CH4-water two-phase flow is introduced and the influence of matrix and fracture and the properties of dual-porosity media of caprock are considered in the model. CH4 and water flow in the fractures of the caprock and CH4 diffuses to the matrix after penetrating the caprock. This model is used to analyze the influence of the CH4 adsorption and diffusion process on the sealing efficiency of the caprock of underground energy storage. The results show that the water saturation of the caprock significantly changes after the gas permeates into the caprock. Adsorption deformation will seriously affect the permeability of the caprock. The longer the adsorption diffusion time is, the worse the sealing performance of the caprock will be. With the increase of the macro-crack length of the caprock, the gas infiltration area around the fracture decreases. Along the bedding direction, the caprock has greater permeability, and gas seepage has a higher speed.