| Description |
In Michigan and surrounding states, anomalous high fluid pressures at depth are attributed to Pleistocene glaciation. Specifically, surface loading of ice and glacial till is hypothesized to compact deep subsurface sediments, and low hydraulic diffusivity of those sediments may require 105 years or longer to equilibrate. Given that the last major glaciation was the Wisconsin glaciation approximately 35,000 years ago, the primary hypothesis tested is whether this conceptual model may explain observed overpressures in the Michigan Basin. The objective of this study was to assemble a meaningful poroelastic algorithm to simulate and quantify the impacts of stress (force) induced by Pleistocene glaciers on deep subsurface fluid pressures. We implemented the simple algorithm in a conventional groundwater flow simulator (TOUGH2, a geothermal reservoir simulator developed by Lawrence Berkeley National Laboratory). Simulation results suggest that excess head may be generated by glacial loading, but for either permeability at the lower end of the range (10-16 m2 or less, approximately), or for ice-loading rates at the upper possible range (approaching 2 cm/year during glaciation). |
