ABSTRACT: Hydrogeochemistry of the Eastern Margin of the Michigan Basin: Implications for Devonian Shale Gas

MCINTOSH, JENNIFER C. and WALTER, LYNN M., University of Michigan, Ann Arbor, MI

Oil and gas field brines in southwestern Ontario have been the focus for several studies on fluid migration within the shallow eastern margin of the Michigan Basin. The Silurian and Devonian formation waters contain brines and petroleum thought to have migrated into the area from the south through underlying strata. Pleistocene meltwater and more modern meteoric recharge also invaded Silurian and Devonian formations along the eastern margin. Recharge of dilute waters can play a key role in generating unconventional biogenic gas deposits where organic rich shale units are in proximity to basin margin recharge.

Recharge of Pleistocene meltwaters to the Devonian Antrim Shale subcrop in northern Michigan critically influenced biogenic gas production. Exploration in the Antrim for unconventional gas has been an enormous success. The best production was associated with relatively shallow wells, which produced a mix of freshwater and basinal brine.

Along the eastern margin of the Michigan Basin, the Antrim Shale subcrops beneath glacial deposits of varying thickness and permeability. This organic rich shale is a regional aquitard. Considering the hydrostratigraphy of the eastern margin, the underlying Devonian carbonate aquifers are a likely avenue for recharge of meteoric waters to the shale. Invasion of dilute waters to the shale along the eastern margin of the basin could have influenced biogenic gas production. Careful investigation of formation waters in the Antrim Shale could provide further evidence for fluid migration along shallow basin margins and potential biogenic gas plays.

Search and Discovery Article #90907©2000 AAPG Eastern Section Meeting, London, Ontario, Canada