An experimental investigation of applicability of CO2 enhanced coal bed methane recovery to low rank coal

Previous studies have shown that carbon dioxide (CO2) injection can enhance CH4 production (CO2-ECBM) compared to traditionally-used methods, mainly due to the higher adsorptive capability of CO2 in coal, which desorbs the CH4 with higher sweep efficiency. Many studies have been conducted to date on the CO2-ECBM technique for high rank coals. However, there have been very few studies on low rank coal. Therefore, this study uses Victorian brown coal samples to investigate the CO2-ECBM potential of low rank coal. A series of CO2 core flooding tests was conducted on CH4 saturated meso-scale brown coal samples for various CO2 injection conditions, phases and pressures.According to the experimental findings, compared to natural recovery, CO2 flooding enhances CH4 production by creating higher production rates, and higher CO2 pressures can drive the CH4 towards the production end with almost 100% sweep efficiency. Furthermore, the rapid CO2 breakthroughs observed under higher CO2 pressures are found to be significant for super-critical CO2. Tests results show that the superior competence of super-critical CO2 in CH4 recovery is independent of coal rank or maturity. However, the greater volumetric strain created by higher CO2 pressures may, have a negative influence on long-term gas productivity with the reduction of flow ability through the seam.