The effects of stress path on compressibilities of coal

A series of pore and bulk compressibility measurements were made on a coal from the Bowen Basin, Queensland, Australia. They were conducted under hydrostatic compression and uniaxial strain conditions. It is found that when a hydrostatic stress is applied the pore and bulk compressibilities of the coal are highly stress dependent. By comparison, the compressibilities of the coal measured under a uniaxial strain condition are smaller in magnitude and much less sensitive to effective stress. This justifies the use of a constant pore compressibility in coalbed methane reservoir simulation. The results with different pore pressures show that the conventional effective stress concept of soil mechanics is valid for the compressibilities of the coal.