Existing subsurface data and data from core and logs in a new CO₂ pilot injection test well drilled in northern lower Michigan were used to evaluate the geological carbon sequestration (GCS) potential in Upper Silurian to Middle Devonian saline reservoir and cap-rock units in the Michigan Basin. The Core Energy-State Charlton #4-30 well, Otsego County, Michigan, was drilled as part of ongoing Midwest Region Carbon Sequestration Partnership (MRCSP) phase II studies to investigate GCS potential in these units in the Michigan Basin. Significant GCS potential is recognized in porous dolomite of the Upper Silurian, Bass Islands Group in the new well. Cherty strata of the Bois Blanc Formation are also present in the #4-30 well but may lack suitable injectivity for consideration of GCS. Argillaceous limestone in parts of the superjacent Amherstburg Formation in the test well contains minimal porosity and permeability and constitutes an excellent cap-rock unit in the area.

Regional consideration of the Bass Islands sequestration target interval indicates substantial GCS potential throughout most of the Michigan Basin. Preliminary estimates of regional GCS storage capacity range from 1.34 billion metric tonnes at 2% displacement storage efficiency to 6.7 billion metric tonnes of CO₂ at 10% storage efficiency in the study area. These displacement storage capacities equate to approximately 288–1440 t of CO₂ per hectare (117–583 t/ac) given the regional estimates of average thickness and porosity in the target interval used here.

Significant drilling fluid loss into the target injection interval observed during drilling of the State Charlton #4-30 well of about 3.2 m³/hr (20 bbl/hr) demonstrates substantial injectivity in the pilot test well. Considering the fluid loss during drilling and measurements of conventional petrophysical properties in the injection target, the proposed CO₂ injection test volume of 10,000 t could fill the target interval in an area of at most 35 ha (86 ac) in the subsurface, depending on displacement storage volume efficiency assumptions. These preliminary assumptions and simple calculations indicate that the CO₂ injection plume for the injection test would extend no more than 600 m (1970 ft) away from the borehole in all directions. Preliminary reservoir simulations, using other assumptions, suggest a substantially less extensive invasion of the target interval during the injection test.