Process involved in enhanced coalbed methane recovery---A literature review

Coalbed methane (CBM) is becoming an important source of energy as conventional reserves are reaching peak production. Primary recovery of CBM entails a de-watering phase of the reservoir in order to lower the pressure in the coalbed sufficiently for methane to naturally desorb. Enhanced coalbed methane (ECBM) recovery is a secondary recovery process that utilizes injection wells to inject gases such as carbon dioxide, nitrogen, and flue gas into the coalbed to aid in the desorption process of methane from the coal. The processes and factors that influence the storage of the injected gas and the release of methane during ECBM recovery are currently under heavy scientific research and few concrete conclusions have thus far been drawn.; The motivation for this study is to collaborate experimental research into one encompassing review paper. It is a literature review of the adsorption/desorption mechanisms that influence the capability of deep unminable coalbeds to retain coalbed methane. These factors include mineral content, maceral content, moisture content, and coal rank. Furthermore, recent experimental studies on enhanced coalbed methane recovery are presented and the processes involved in carbon dioxide and nitrogen injection are described. This study focuses on preferential adsorption of methane, nitrogen, and carbon dioxide. Swelling and shrinkage effects experienced by the coal upon adsorption and desorption of gases is explored and a theoretical model is presented. The Langmuir, Brunauer-Emmett-Teller (BET), Dubinin-Astakhov (D-A), and Dubinin-Radushkevich (D-R) isotherm models are reviewed, and a description of the diffusion process that occurs as gas enters the pore structure of the coal is given.