Permeability and injectivity improvement in CO2 enhanced coalbed methane recovery: thermal stimulation of the near wellbore region

Loss of injectivity in the near wellbore region of coalbeds during CO2 injection is a limiting factor for its exploitation as potential reservoir for geological storage of CO2. Current research investigated the potential of thermal stimulation (thermal fracturing through cyclic freezing and thawing) of coal at the wellbore in order to achieve better injectivity during enhanced coalbed methane (CBM) recovery and CO2 storage. Moisture saturated coal samples were subjected to freezing and thawing cycles to establish the effects of this treatment on coalbed reservoir and elastic properties which can affect CO2 induced swelling stress and permeability. Volumetric swelling strains were found to be reduced for thermally stimulated coal, resulting in improved permeability. The experimentally measured porosity, elastic modulus and swelling coefficients were then used in an analytical wellbore model to assess the impact of thermal stimulation on near wellbore permeability. Through reservoir simulation studies it was observed that the thermally stimulated zone can potentially improve CO2 injectivity and enhance methane production.