Gas, hydrates, and submarine landslides
December 12, 2023
CSEE Webinar
Bio: Hugh Daigle is an associate professor in the Hildebrand Department of Petroleum and Geosystems Engineering at the University of Texas at Austin. He holds a BA magna cum laude in Earth and Planetary Science from Harvard University and a PhD in Earth Science from Rice University. Prior to joining the PGE faculty in 2013, he worked as a petrophysicist at Chevron. Hugh’s research interests include gas hydrates, submarine geohazards, sustainable energy, and uses of nanotechnology in oil and gas production.
Abstract: Submarine landslides on passive continental margins remain enigmatic as their triggers and preconditioning factors are poorly understood. Gas hydrates and subsurface gas accumulations are frequently implicated, but little evidence has been collected linking these features to slope failure. We spent 33 days at sea in May and June 2023 collecting 3366 km of 2D seismic data and 80 m of sediment cores at the Cape Fear Slide (CFS) offshore North Carolina. The CFS is a well-studied example of a large, open slope-sourced submarine landslide on the eastern North American margin with evidence of multiple episodes of failure. A seafloor-breaching salt diapir, the Cape Fear Diapir, occurs just downdip of the main CFS headscarp. Our newly acquired data show that the CFS is seaward of a buried Miocene shelf-edge delta containing gas, with the thickest, most continuous gas column occurring beneath the CFS source area. Gas chimneys are evident within and above the shelf-edge delta; they approach the present-day seafloor but do not appear to breach it. We postulate three scenarios to explain the preferential accumulation of gas beneath the CFS. First, the thicker cover above the clinoform structure under the CFS allows more efficient trapping of gas, while farther to the north the clinoform package is closer to the seafloor or not present, potentially lacking a reservoir for gas accumulation and allowing gas leakage. Second, the seafloor-breaching Cape Fear Diapir downdip of the CFS source area may provide gas migration pathways around its flanks directly to the clinoform structure, while to the northeast the salt diapirs do not come as close to the seafloor and may not provide sufficient gas supply. Third, there may be a stronger gas charge, possibly related to variations in lithology, beneath the CFS as evidenced by the deep-rooted chimney structures. The largest recent submarine landslides on the margin tend to be seaward of shelf-edge deltas or seafloor-breaching salt diapirs, and our data whereby gas interacts with these features to precondition and possibly trigger slope failure. Multiple cycles of gas accumulation and release could be implicated in repeated slope failures.
