A laboratory investigation of the impact of solvent treatment on the permeability of bituminous coal from Western Canada with a focus on microbial in-situ processing of coals

Coal biogasification via microbial metabolization has great potential to produce renewable methane and facilitate carbon dioxide sequestration while multiple challenges still remain to tackle especially the deficiency of direct permeability measurements. The pulse decay method has been performed on high-volatile bituminous coals from Western Canada to investigate permeability variations for raw, solvent soaked and solvent-extracted samples under variable confining and pore pressures. Coal permeability decreases with respect to increasing confining pressure while it increases tens of times with respect to increasing pore pressure. The vertical permeability is about one order of magnitude lower than horizontal one, indicating highly anisotropic nature of coal. Coal bioconversion stimulation by adding solvent may trigger a series of coal–solvent interactions due to matrix swelling. Coal permeability drops about one order of magnitude after soaked in toluene and dichloromethane but less dramatic in hexane. However, solvent-extraction and sorptive material removal can reduce the swelling strain and increase permeability about two orders of magnitude. Coal matrix swelling and shrinkage in solvent, coupled with the effects of external effective stress, make coal permeability relationships complicated and a deeper understanding of these processes is needed for coal bioconversion application in fields.