Seismic characteristics and strain of coal during the sorption of CO2 and CH4

Coal has been studied for its extensive capability of adsorbing CO2 in exchange for coalbed CH4. Various sorption models have been developed and enhanced in order to precisely understand the implications of carbon sequestration and enhanced coalbed CH4 recovery processes. Our study aims at analyzing the characteristic behavior of a bituminous coal in various CO2 and CH4 pressure environments through seismic waveform and strain analyses. Laboratory-scale geophysical investigation of a coal specimen was performed under pressures of up to 1000 psi for CH 4 and up to 700 psi for CO2. The results show that the coal specimen has a significantly higher rate of swelling from CO2 injection than CH4. The coal specimen shows instability to reach equilibrium at higher CO2 pressure level; micro-bedding layers of the coal specimen exhibit high seismic impedance at atmospheric pressure, which decreases concurrently as CO2/CH4 pressure increases. The results also show that the coal experiences different rates of swelling and shrinkage for CO2 and CH4 in a confined pressure environment, after a given time interval.