Characterization of shales from Damodar valley coalfields for CH4 recovery and CO2 sequestration

Abstract

Anthropogenic emission of greenhouse gases particularly, CO2 is believed to be responsible for the global climate change. Carbon sequestration has been identified as one of the technological alternatives of reducing CO2 emission from the atmosphere. Disposal of CO2 in unconventional reserves such as shale formations may help in achieving the objectives of sequestration of the CO2 coupled with enhanced recovery of methane. The methane/CO2 storage potential of shale mainly depends on its porous nature which is very complex due to the presence of micro-, meso-, and macro-pores. Understanding the pore size distribution of shales is important because the storage and transport mechanisms of methane and CO2 vary as per the size of the pore. Further, the clay minerals present may also contribute significantly to the adsorption capacity of shale and may thus control the gas storage. In the present study, an attempt is made to investigate the pore structure of some shale samples from Damodar valley coalfields (Jharia and Raniganj coalfields), India in detail and correlate the pore parameters with adsorption of methane. Secondly, the clay mineral composition of studied shales is analyzed and its effect on porosity and adsorption are examined. Low pressure nitrogen and carbon dioxide adsorption tests, mercury intrusion and helium pycnometry tests are carried out to ascertain the pore sizes, surface area, and pore volume. It is observed that the porosity for most of the studied shales are dominated by mesopores. A moderate correlation is observed between nitrogen BET surface area and porosity suggesting lesser amount of micropores and dominance of mesopores. Porosity of the studied shales varied with clay mineral content exhibiting a U-shaped relationship.