PREDICTING ENERGY GAS STORAGE CAPACITY IN DEPLETED HYDROCARBON RESERVOIRS: INSIGHTS FROM EXISTING STORAGE FACILITIES IN THE MICHIGAN BASIN

The short-term storage of natural gas in geologic settings, such as depleted hydrocarbon reservoirs and solution mined salt caverns, is an important component for reliable seasonal energy delivery in the United States. Additionally, as power generation increases from more intermittent renewable energy sources (e.g., wind and solar), expanding subsurface storage capacity of natural gas, along with hydrogen, for peak electricity generation is one strategy to improve resilience of a lower carbon electrical grid. Here, we present methods for quantifying natural gas storage capacity in depleted conventional gas reservoirs in the Michigan Basin as part of a broader national assessment of subsurface energy storage resources by the U.S. Geological Survey (USGS). Storage capacity estimates are based on historical oil and gas production statistics, volumetric parameters, and historical pressure data for reservoirs in Michigan. Data are derived from the 2018 USGS Comprehensive Resource Database – a national-scale proprietary database. Nationally, the state of Michigan has both the greatest number of operating underground gas storage (UGS) facilities and the largest developed working gas (WG) capacity – defined as the volume of gas that can be injected into and withdrawn from a UGS facility, typically on annual timescales. We compared reported reservoir WG capacities from about 30 existing UGS facilities with predicted WG capacity estimations to evaluate error associated with calculations derived from different input parameters (e.g., production vs. volumetric vs. pressure data). Statistical models under development allow us to identify significant input parameters for predicting WG capacity, such as the cumulative gas production from a reservoir. Preliminary comparisons show broadly reliable agreement (r² = 0.90) between predicted WG storage capacity estimates and the WG capacity data reported for the reservoirs by UGS facility operators to federal regulators. This study, while specific to the Michigan Basin, outlines requisite reservoir parameters and data needed to predict storage capacities in conventional reservoirs that may be candidates for conversion from producing natural gas to the subsurface storage of energy gases.