CH4–CO2 gas exchange and supercritical CO2 based hydraulic fracturing as CBM production-accelerating techniques: A review

Abstract

CH4–CO2 gas exchange and CO2 based hydraulic fracturing are common enhancement techniques adopted in coal-bed methane (CBM) extraction industry, with promising results. This review provides a comprehensive overview of the CH4–CO2 gas exchange method at macro and microscopic level, and the CO2-based hydraulic fracturing. The process of CH4 replacement by CO2 is comprehensively discussed considering two possible CBM storage mechanisms; 1) by adsorption and; 2) at hydrate state. The CH4–CO2 gas exchange by sorption/diffusion process has been proven to be kinetically and thermodynamically viable as CO2 can easily penetrate through ultra-micro-pores region and adsorb into the coal pores due to it..