Carbon dioxide (CO2) capture, utilization and storage (CCUS) are considered as an effective approach to mitigate carbon dioxide emissions into geologic formations. Deep unmineable coal seams have been identified as a possible option for Malaysian case, because it has large CO2 adsorption capacity, long time CO2 trapping and extra enhanced coal-bed methane recovery (ECBMR) and CO2 sequestration. The current practice for recovering coal bed methane is to depressurize the bed, usually by pumping water out of the reservoir, the desorption of gas from coal surface, diffusion of gas to the fracture systems, and flow of the gas through the fractures to the wellbores. Hence, an alternative approach is to inject CO2 into the coal bed seams to increase the mobililbity of methane recovery. As a result induced adsorption strain (swelling) is one of the main difficulties which face CO2 sequestration in coal seams. This phenomenon occurs, particularly when the injected carbon dioxide adsorbs on surface of the coal pores and interacts with coal in chemi-physical adsorption isotherm under extreme conditions, which causes the coal to swell. This swelling in confined conditions leads to a closure of coal matrix pores and cleat system, which hinders further CO2 injection. However, swelling will decrease permeability and adsorption capacity of coal seams and increases CO2 injectability potential complications. The degree of swelling would be affected by many parameters such as coal rank, water content and petrographic content, mechanical properties (e.g., stress levels and confinements), operating conditions (e.g., gas injection pressure and temperature), free gas and fluid type. Thus these parameters have significant affect on CO2 continuous injection process in coal seams in long term. This paper is emphasis on these main parameters which have influence on coal swelling during carbon dioxide injection in coal specimens. |
