Mechanism of CO2 enhanced CBM recovery in China: a review

Permeability of coal reservoirs in China is in general low. Injection of CO2 into coal seams is one of the potential approaches for enhancing coalbed methane (CBM) production. The feasibility of this technology has been investigated in China since the 1990s. Advances in mechanism of CO2 enhanced CBM recovery (CO2-ECBM) in China are reviewed in light of certain aspects, such as the competitive multi-component gas adsorption, sorption-induced coal swelling/shrinkage and its potential effect on CBM production and numerical simulation for CO2-ECBM recovery. Newer investigations for improving the technology are discussed. It is suggested that a comprehensive feasibility demonstration in terms of geology, technology, economics and environment-carrying capacity is necessary for a successful application of the technology for CBM recovery in China. The demonstration should be carried out after more investigations into such facets as the control of coal components and structure to a competitive multi-component-gas adsorption, the behavior and essence of supercritical adsorption by coal of gas, environmental and safe feasibility of coal mining after CO2 injection and more extensive pilot tests for CO2-ECBM recovery.