Monitoring Salt Domes Used for Energy Storage With Microseismicity: Insights for a Carbon‐Neutral Future.

Omojola, Joses; Persaud, Patricia

Underground storage in geologic formations will play a key role in the energy transition by providing low‐cost storage of renewable fuels such as hydrogen. The sealing qualities of caverns leached in salt and availability of domal salt bodies make them ideal for energy storage. However, unstable boundary shear zones of anomalous friable salt can enhance internal shearing and pose a structural hazard to storage operations. Considering the indistinct nature of internal salt heterogeneities when imaged with conventional techniques such as reflection seismic surveys, we develop a method to map shear zones using seismicity patterns in the US Gulf Coast, the region with the world's largest underground crude oil emergency supply. We developed and finetuned a machine learning algorithm using tectonic and local microearthquakes. The finetuned model was applied to detect microearthquakes in a 12‐month long nodal seismic dataset from the Sorrento salt dome. Clustered microearthquake locations reveal the three‐dimensional geometry of two anomalous salt shear zones and their orientations were determined using probabilistic hypocenter imaging. The seismicity pattern, combined with borehole pressure measurements, and cavern sonar surveys, shows the spatiotemporal evolution of cavern shapes within the salt dome. We describe how shear zone seismicity contributed to a cavern well failure and gas release incident that occurred during monitoring. Our findings show that caverns placed close to shear zones are more susceptible to structural damage. We propose a non‐invasive technique for mapping hazards related to internal salt dome deformation that can be employed in high‐noise industrial settings to characterize storage facilities. Plain Language Summary: In the shift toward renewable energy, underground storage is vital for increasing the feasibility of fuels like hydrogen. Salt formations are ideal for storage, and caverns in salt domes are used worldwide to store vast amounts of energy reserves. But salt domes can become unstable and lead to cavern collapse, posing risks to the environment and nearby communities. Traditional methods are expensive, often require drilled wells, and do not always spot hazards. We instead used recordings of ground shaking from small earthquakes to identify them. By collecting these recordings for over a year with an array of instruments installed at the surface over a Louisiana salt dome, we were able to develop a new method for identifying very small earthquakes, allowing us to pinpoint hazardous areas. Our approach offers a non‐invasive way for scientists and engineers to assess hazards and mitigate risks associated with drilling and underground storage operations in salt domes. Key Points: Passive seismic monitoring with surface arrays is a non‐invasive approach for identifying hazards in salt domesMicroearthquakes detected with our finetuned machine learning model illuminate shear zone geometries and structural hazardsCavern storage wells drilled within proximity of shear zones are at risk of safety incidents

MACHINE learning; SALT domes; SHEAR zones; GEOLOGICAL formations; UNDERGROUND storage

Geochemistry, Geophysics, Geosystems: G3, 2024, Vol 25, Issue 11, p1

1525-2027

Academic Journal

10.1029/2024GC011573