Impact of Coal Compressibility OnCoalbed Methane Production: A Comparison Study of Malaysian Coal to Other CBM Fields

The purpose of this research is to explain the relationship between the coal compressibility and the subsequent impact on the gas production in a coalbed methane reservoir. Coalbed methane is a type of unconventional source of petroleum, in which the methane gas is stored in the coalbed reservoirs, which act as both source rock and reservoir rock. Unlike conventional reservoir rock properties, coal has dual-porosity characteristics. 95% of the gases are stored in micropore via adsorption in the matrix of the coal, best describes with Langmuir Adsorption Isotherm. The remaining gases are stored as free gas in the macropore, also known as the cleat system of the coal, made up of butt cleats and face cleats. After ‘dewatering’ during the production stage of coalbed methane, gases in the micropore of coal will be desorbed and flow into the cleats. At this stage, the coal undergoes several compressibility changes due to the change in effective stress and the matrix shrinkage as gases desorbed from coal matrix. The changes in the bulk compressibility, pore compressibility, matrix compressibility and matrix shrinkage compressibility will have impacts on the permeability of the coal, which ultimately have an impact on CBM production. Hence, laboratory experiments will be conducted to investigate the relationship between these compressiblities and the permeability of the coal samples. Subsequently, the production potential of the Malaysian coal samples can be determined via simulation studies and compared to other actual producing coalbed methane fields. Keywords: coalbed methane, compressibility, permeability, production