International Journal of Mining Science and Technology (Jun 2023)
Research on the feasibility of storage and estimation model of storage capacity of CO2 in fissures of coal mine old goaf
Abstract
The concept of the carbon cycle in the old goaf of a coal mine based on CO2 utilization and storage was put forward adhering to the principle of low-carbon development, utilization of space resources in old goafs, and associated gas resources development. Firstly, the evolution characteristics of overburden fissures in the goaf of the case was studied using a two-dimensional physical similarity simulation test, the sealing performance of the caprocks after stabilization was analyzed, and the fissures were counted and classified. Then, the process of gaseous CO2 injection in the connected fissure was simulated by Ansys Fluent software, and the migration law and distribution characteristics of CO2 under the condition of gaseous CO2 injection were analyzed. Finally, the estimation models of free CO2 storage capacity in the old goaf were constructed considering the proportion of connected fissure and the effectiveness of CO2 injection. The CO2 storage capacity in the old goaf of the case coal mine was estimated. The results showed that a caprock group of “hard-thickness low-permeability hard-thickness” was formed after the caprock-fissures system in the goaf of the case tended to be stable vertically. The connected fissure, occlude cracks, and micro-fractures in the goaf accounted for 85.5%, 8.5%, and 6% of the total fissures, respectively. Gaseous CO2 first migrated to the bottom of the connected fissure after CO2 was injected into the goaf, then spread horizontally along the bottom of the connected fissure after reaching the bottom, and finally spread longitudinally after filling the bottom of the entire connected fissure. The theoretical and effective storage capacities of free CO2 at normal temperature and pressure in the old goaf of the case were 9757 and 7477 t, respectively. The effective storage capacity of free CO2 at normal temperature and pressure in the old goaf after all minefield mined was 193404 t. The research can provide some reference for the coal mining industry to help the goal of “carbon peaking and carbon neutrality”.
