대수층 내 CO2 지중저장 시 지층의 물성에 따른 균열 활성화 분석

Abstract

Geologic CO2 storage in aquifer is one of several important options of solving global warming effect caused by greenhouse gas emission. The injection of CO2 increases pore pressure and induces change of mechanical state. It is expected to be a cause of fracture reactivation which is an important issue for the safety of CO2 storage. Using the geomechanical module, fracture reactivation induced by tensile fracturing was considered to investigate potential of CO2 leakage caused by mechanical failure. To describe the modification of fracture permeability, modified Barton-Bandis model was applied. Extensive numerical simulations were conducted to analyze the effects of rock properties and trapping mechanisms on fracture reactivation. The effects of Young’s modulus, Poisson’s ratio, permeability, solubility, and residual gas trapping were analyzed. Change of stress state, deformation of rock and pressure buildup induced by CO2 injection were also presented. The time for occurrence of fracture reactivation was compared. When rock has high Young’s modulus, effective stress decreases rapidly. Compared to the case of low Young’s modulus, effective stress begins to decrease in early time and fracture is reactivated quickly. Young’s modulus of aquifer has great effects on fracture reactivation. Poisson’s ratio affects not the time for beginning to reduce effective stress but the amount of reduction in effective stress. Total amount of reduction in effective stress in the rock with low Poisson’s ratio is less than that of rock with high Poisson’s ratio. In the rock with low Poisson’s ratio, fracture opening appears lately. Poisson’s ratio of caprock has greater effect on the reactivation of fracture than that of aquifer. High permeability reduces the magnitude of pressure buildup caused by CO2 injection. In this condition, fracture is reactivated lately. Effects of aquifer permeability are larger than that of caprock. Solubility trapping affects the distribution of CO2 phase and influences fracture reactivation, whereas residual gas trapping has no effect on reactivation of fracture. This paper broadens our perception into mechanical behavior induced by CO2 injection and could be helpful for precise safety assessment of CO2 storage project.