CHARACTERIZING DEPLETED RESERVOIRS AS PORE SPACE FOR STORAGE OF NATURAL GAS AND OTHER ENERGY GASES IN MICHIGAN BASIN

Energy consumption in the United States (U.S.) is shifting away from traditional fossil fuels like coal and oil, and towards natural gas and renewable sources, potentially including hydrogen. Because gas demand is typically greatest during cold seasons and renewable sources sometimes produce variable supplies, it is important to store energy for use when demand exceeds supply. Whereas batteries and tanks typically store energy above ground, geologic (underground) storage may be able to retain much greater quantities of energy, especially as compressed gases, over much longer durations. Consequently, we developed an approach to locate new geologic energy storage sites and estimate associated pore space capacity with an initial focus on amenable depleted gas reservoirs.

Depleted hydrocarbon fields in Michigan Basin host large quantities of injected natural gas (about 681 billion cubic feet of seasonal gas capacity in 42 facilities). Therefore, we use this basin to characterize potential new storage alongside existing gas storage facilities. To find additional sites, we searched for reservoirs with wells that had a pause in production for five years or greater, as determined from our statistical analysis of well activity. As a result, we located two amenable reservoirs in Mississippian Michigan Formation (Stray) sandstones and five in Silurian Burnt Bluff Group dolomites. Our preliminary estimate of new storage resources in these seven reservoirs would add about 25% to the existing working gas capacity in just these two formations. This estimate is based on reservoir volumetric calculations and typical seasonal to total gas ratios observed in operating facilities. In addition, since the 1950s when many existing facilities were converted to storage, we calculate that capacities grew about 30%, indicating both the need for additional storage and increased energy demand overall.

Follow-on work would estimate storage capacity for other gases alongside natural gas in pore space in these and other amenable formations in Michigan Basin, such as Silurian Niagara Group pinnacle reefs, where stored gas occupies vuggy porosity. This study is part of our work evaluating U.S. sedimentary basins and quantitatively assessing amenable reservoirs to derive regional probabilistic estimates of storage capacity using statistical aggregation to correctly propagate uncertainties.