Staged numerical simulations of supercritical CO2 fracturing of coal seams based on the extended finite element method

Abstract

As a water-less fracturing mining technology, supercritical CO2 (SC-CO2) fracturing has attracted increasing attention in the mining industry. In order to simulate the whole process of SC-CO2 fracturing and fully understand the fracturing mechanism of SC-CO2, the thermodynamic analysis method was used to analyze the phase transitions of CO2 in SC-CO2 fracturing, and the whole process of SC-CO2 fracturing was divided into the SC-CO2 fracturing stage and the CO2 phase-transition induced fracturing stage. Based on the extended finite element method, the fluid-solid coupling model at the SC-CO2 fracturing stage, the TNT equivalence of CO2 phase transition induced fracturing, pressure-time history curves of blast loads, and numerical model of CO2 phase transition induced fracturing stage were comprehensively analyzed, and the staged numerical simulation method of SC-CO2 fracturing was proposed. The simulation results showed that cracks in the coal seam were initiated and propagated at the SC-CO2 fracture stage, and the cracks broadened, and new cracks were generated during the CO2 phase-transition induced fracturing stage. At the same time, the injection rate of SC-CO2 fluid had a positive impact on its fracturing effect. The larger the injection rate of SC-CO2 fluid, the larger the length and width of crack propagation. This study is of great significance for enriching SC-CO2 fracturing theory.