Evaluation of Energy Storage Potential of Unconventional Shale Reservoirs Using Numerical Simulation of Cyclic Gas Injection

Abstract

Compressed-air energy storage (CAES) stores energy as compressed air in underground formations, typically salt dome caverns. When electricity demand grows, the compressed air is released through a turbine to produce electricity. CAES in the United States is limited to one plant built in 1991, due in part to the inherent risk and uncertainty of developing subsurface storage reservoirs. As an alternative to CAES, we propose using some of the hundreds of thousands of hydraulically fractured horizontal wells to store energy as compressed natural gas in unconventional shale reservoirs. To store energy, produced or “sales” natural gas is injected back into the formation using excess electricity and is later produced through an expander to generate electricity. To evaluate this concept, we performed numerical simulations of cyclic natural gas injection into unconventional shale reservoirs using CMG-GEM commercial reservoir modeling software. We tested short-term (diurnal) and long-term (seasonal) energy storage potential by modeling well injection and production gas flow rates as a function of bottom-hole pressure. First, we developed a conceptual model of a single fracture stage in an unconventional shale reservoir to characterize reservoir behavior during cyclic injection and production. Next, we modeled cyclic injection in the Marcellus shale gas play using published data. Results indicate that Marcellus unconventional shale reservoirs could support both short- and long-term energy storage at capacities of 100-1,000 kWe per well. The results indicate that energy storage in unconventional shale gas wells may be feasible and warrants further investigation.

Electrical energy storage using compressed gas in depleted hydraulically fractured wells

“…No leak-off was observed beyond the boundary of the unstimulated matrix in our simulated cycles. Details of the model are found in Augustine et al. (2021a) and outlined in the STAR Methods section.…”

“…The LCOS model is described in detail in the text. The well bore and surface machinery models are thoroughly described in the main text, but the reservoir model was first described in detail in Augustine et al. (2021a) .…”

“…The ability to predict and control injection and production of natural gas into and from a shale reservoir through a hydraulically fractured well is one of the most important and challenging aspects of the REFRAES concept. In an earlier study, using data from dry gas shale plays such as the Marcellus, Haynesville, and Barnett, we completed extensive reservoir modeling( Augustine et al., 2021a ) for the injection and production flow rates, pressures, temperatures, and reservoir response during cyclic injection and production of natural gas under energy storage operations. The gas injection occurs near the natural reservoir temperature, pressure, and flow rate, so reservoir deterioration is unlikely.…”