Idle Wells Could Provide Paths to Large-Scale Subsurface Energy Storage
Opportunities are created at the intersection of two important energy problems—the need for large-scale, long-term energy storage systems and effective end-of-life field management of historical oil and gas assets. This paper presents a hyperscale energy-storage solution using repurposed idle oil and gas wells to store energy in subsurface saline aquifers.
The continued adoption of intermittent renewable-power generation sources, such as wind or solar, requires large-scale, long-duration energy storage to buffer the intermittency of renewable power sources to supply 100% dispatchable power whenever it is needed. When required for durations longer than 24 hours and at large scale (500 MW or more), current energy storage solutions offer only 4–10 hours storage, becoming prohibitively expensive, as in the case of batteries or site-constrained and environmentally challenged pumped hydro systems.
This paper presents a hyperscale energy-storage solution using repurposed idle oil and gas wells to store energy in subsurface saline aquifers. The screening criteria for suitable subsurface saline aquifers that can be accessed via idle oil and gas wells is discussed. Repurposing idle wells or subsurface energy storage could provide an alternative to costs associated with traditional well abandonment and remediation. Repurposing idle wells could also provide a means for reducing current methane emissions. The proposed zero-carbon storage solution offers energy-storage durations much longer than available alternatives, making possible a national grid with 100% variable renewable generation from solar and wind and the retirement of many fossil-fuel plants.
Conventional compressed air energy storage plants operate with low efficiency and use salt caverns. Scaling up for a longer duration becomes expensive and site-constrained because they are contingent on the availability of large-volume salt caverns. They use natural gas to heat expanding air through gas turbines for power generation and, thus, are not zero-carbon operations. While the current focus is on the approximately 38,000 idle wells in California, the proposed process and associated storage system could well apply broadly to the many US and global petroleum operations with large inventories of aging and idle oil and gas wells.
Opportunities are created at the intersection of two important energy problems—(1) the growing need for large-scale, long-term energy storage systems to match the expected expansion of renewable-power generation capacity and (2) the effective end-of-life field management of historical oil and gas assets, particularly regarding the large and growing inventory of idle wells. The initial focus of the proposed solution is the California energy system, given both its electric power system and its large inventory of historical oil-producing infrastructure. The operational and technical developments discussed here, however, could be applicable to other mature oil and gas producing basins.