Numerical simulation study on CO2 storage in coalbed

Abstract

ABSTRACTAlthough CO2 storage has been comprehensively investigated, fewer scholars have taken the effect of temperature and the dual-porosity structure of coal into account, which brought a large deviation for the study of CO2 storage. In this work, a hydraulic-mechanical-thermal coupled model of CO2 storage is established, considering the dual-porosity structure features and non-isothermal adsorption of coal. The controlled variable method was used to simulate CO2 injection into coalbed with different characteristic parameters. The results show that the CO2 storage rate follows the law of first reducing and then stabilizing. The variation of permeability is a competition result of two types of factors: one is the coal matrix shrinkage caused by pressure increase and the other is the coal matrix expansion caused by the increase of temperature and CO2 adsorption. In the process of CO2 injection into the coal seam, the matrix expansion caused by the increase of temperature and CO2 adsorption becomes the dominant role, which makes the permeability reduce with time. The higher the initial temperature of coal seam, the less the volume of CO2 adsorbed by the unit mass of coal and the smaller the CO2 storage rate; the greater the degree of coal fracture development, the greater the CO2 seepage rate, the smaller the CO2 storage rate, and the increased volume strain of coal, which can reduce the storage rate of CO2. The initial temperature of coalbed, fracture development degree, and geostress have different degrees of influence on CO2 storage. Taking CO2 storage rate as an evaluation criterion, the fracture development degree has the greatest impact on it, and the influence of geostress is the least.