Geologic sequestration of anthropogenic greenhouse gases into deep geological reservoirs like coal seams has caught attention worldwide. The potential of coal to adsorb CO2 and preferentially release methane partly offsets the cost of capture, transport and storage of the gases. For such projects, it is important to understand the influence of geomechanical properties of coal on cap rock integrity and long term safety. However, coal being highly heterogeneous from basin to basin, seam to seam, and those within the seam, it is difficult to determine the properties of the complete seam. This makes it difficult to characterize and understand the coal properties for developing ideal models for optimization of sequestration process and generating useful correlations. Therefore, in this study, reconstituted bituminous coals were used in the laboratory experiments to overcome the problem of heterogeneity. It was found that the mechanical properties of reconstituted coal like density, strength, etc. were quite homogenous as compared to the natural samples. The samples were tested for their geomechanical attributes after sustained exposure in a carbon dioxide environment. The saturated strength of coal were nearly 3–4% lesser than the strength of intact reconstituted coal specimens. This study may be very useful and extended for further investigation on coals overcoming the difficulty of the heterogeneity.
Geologic sequestration of anthropogenic greenhouse gases is being viewed as one of the most feasible options for preventing their release in the atmosphere (Bachu 2002, Perera et al. 2011, Shukla et al. 2010, Vishal et al. 2013a,b). Deep seated coal seams offer opportunities for storage of carbon dioxide for geologically significant periods of time.The unmineable coal seams may have potential for production of coalbed methane (CBM). The economics analysis states that the recovery of the partly offsets the cost of CO2 capture, compression, transport and storage. During enhanced CBM recovery, CO2 is injected into the coal seams and is used to extract methane. Injected CO2 reduces the partial pressure of methane and enhances its desorption from the matrix (White et al. 2005). Furthermore, CO2 is preferentially adsorbed onto the porous surface of the coal thereby displacing methane from adsorption sites. In coals where the quantities of methane are not significant, injection of CO2 may be carried out solely for storage purposes. Understanding the geotechnical characteristics of coal is key to successful sequestration operations. The major challenge to understand coal behaviour is due to its high anisotropy and heterogeneity. Therefore, in this study, reconstituted Indian coals were developed and the same were treated with CO2 exposure and the changes in coal characteristics were monitored.
