Measurement of Evolving Compression Coefficients of Fractures during Gas Injection
摘要
The compression coefficient of fractures in coal is a critical parameter that affects the transport and storage of methane within coal seams. We explore the evolution of the compression coefficient driven by a complex interaction of gas adsorption, gas pressure under evolving confining stresses. Permeability and overall strain are recorded while injecting sorbing carbon dioxide at a constant pressure of 3 MPa while cycling confining stress from 5–10 MPa and alternately non-sorbing Helium at pressures of 0.5 and 1 MPa with confining stresses ranging from 2–10 MPa. Permeability decreases with gas adsorption during CO2 injection as overall strain increases (dilation) before decreasing as confining pressure is increased. The compression coefficient of the fracture was obtained from measured coal permeability to CO2 and He. Regarding CO2, data revealed that the Compression coefficient decreased with increasing confining stress across all cycles when saturated with CO2. The compression coefficient initially decreased rapidly before slowing. This temporal response also revealed a progressive increase in compression coefficient with repeated loading cycles due to the dilation of the fracture due to the adsorption of CO2. For He, the results showed that higher confining stress results in reduced compression coefficient. However, higher gas pressure increases compression coefficient. Observations indicate that confining pressure, gas adsorption, and gas pressure are the main factors influencing response, ranked by their significance in that order.