Semester of Graduation

Spring 2023

Degree

Master of Science (MS)

Department

Geology and Geophysics

Document Type

Thesis

Abstract

Safely transforming geological formations into cost-effective underground storage is critical for the US energy security and global energy transition. Seasonal energy demand requires relatively cheap, impermeable, non-reactive materials for storing vast amounts of natural gas and hydrogen. Due to their low risk of fracturing and leakage, salt formations are ideal for these purposes however, pressure variations during drawdown, differential salt creep, and reactivation of pre-existing fractures along boundary shear zone(s) (BSZ) can be detrimental to salt cavern safety and long-term cavern operations. Several environmental disasters at storage facilities in the US and Europe, have created a need to understand how these processes can lead to a disruption of cavern operations. Using 12 months of nodal seismic data recorded at the Sorrento salt dome, Louisiana, we evaluate the suitability of microseismic methods for monitoring subsurface changes at underground storage sites. Due to the poor performance of traditional earthquake detection methods in high-noise settings with multiple anthropogenic and natural noise sources, we developed a hybrid U-Net model capable of effectively detecting microseismic events. Our catalog contains over 112 microearthquakes with moment magnitudes between -2 to 2 Mw. The microearthquakes occur mainly along two N-S trending BSZ with documented cavern instabilities and failures. Seismicity along one BSZ was linked to casing fracture along a wellbore, pressure loss, and deformation in the underlying cavern. This study establishes the usefulness of our approach for monitoring underground storage facilities from site selection to abandonment.

Date

4-4-2023

Committee Chair

Persaud, Patricia

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