Imaging Fault-Aquifer Interactions in the US Gulf Coast Energy Corridor: Implications for Contaminant Flow

Session: Faults, Fractures, and Geomechanics for the Energy Transition

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Abstract:

The increasing risks to water resources is a world­wide environmental problem. In the US Gulf Coast, water quality degradation from salinization is a pervasive issue that results from a combination of natural and anthropogenic processes. In southern Louisiana, the Tepetate-Baton Rouge fault system is a set of regional growth faults with documented damage to surface infrastructure. Understanding the role the faults play as a conduit-barrier to the migration of saline water is critical for salinization control in the region. While fault slip is mostly aseismic, human activities such as oil and gas production, and groundwater extraction may affect fault behavior and their interactions with the surrounding aquifer systems. Significant subsidence and accelerating aquifer contamination with saline waters have raised concerns about potential changes in fault slip and fault zone permeability, and the impacts on groundwater flow. To investigate these interactions, we use data from five dense linear seismic arrays of 428 three-component nodes installed in southern Louisiana with two arrays in the capital city of Baton Rouge. The arrays have a ~200 m inline spacing and recorded at 500 Hz from October to November 2022. We use ambient noise tomography and horizontal-to-vertical spectral ratios (HVSR), integrated with LiDAR, well-log data, and USGS airborne electromagnetic data to construct the first high-resolution subsurface images of the fault zones and aquifer systems. The velocity profiles and HVSR curves show a low-velocity layer between 150 and 200 m depth, corresponding to the shallow wedge-shaped sand bodies of the freshwater aquifer. Aquifer units are mapped down to ~2 km depth to the top of the marine shales. However, their lateral continuity is affected by the Baton Rouge and Mamou faults differently and in different locations, indicating that some fault segments are barriers while others act as conduits to fluid migration, and fault zone architecture and hydraulic properties may also vary over time. We discuss the implications of our results and for groundwater contamination and sustainable water resource management.