Glacially-induced hydromechanical coupling in shale may have caused underpressured water in the eastern Michigan Basin despite the possible presence of gas phase methane

When glacial cycles occur above low-permeability geologic formations, such as the shale and limestone units being considered for nuclear waste disposal in Canada, pressures may differ greatly from normal hydrostatic conditions. Although shale also often has the propensity to generate separate phase fluids like natural gas, it is largely uncertain how the processes that control this behavior might affect water pressure evolution during loading cycles. Therefore, this study investigates the relationships among these fundamental system components via an example site that exhibits both a dramatic underpressure and potential evidence for gas phase methane in situ. A simple 1-D representation of the site was constructed, and hydromechanical coupling during a glacial cycle was simulated with and without gas phase methane present. Results indicate that, while the presence of gas phase dampened the effects of the loading cycle due to its higher compressibility compared to water, it did not preclude underpressure development.