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Observations and Interpretation of the Salt Keel Features in U.S. Gulf of Mexico, Keathley Canyon Protraction Area and 2-D Restoration of a Cross-Section


Salt “keels” are often referred to as a geologic low compared to the surrounding level of the base of salt geobodies. Salt keels in the allochthonous salt canopy are observed in the US Gulf of Mexico, Keathley Canyon area. Various segments of keels are mapped inboard (~5-15 miles) of and subparallel to the Sigsbee Escarpment (~100 mile long). The prior absence of high-quality, depth-migrated, subsalt seismic data have hindered interpretations of these structures. Salt keels were historically linked to local, deep salt feeders based on old seismic images. With advances in the seismic data quality, recent studies describe the keel structure in a portion of Keathley canyon as an independent shallower allochthonsous salt structure without linkage to the deep salt. However, there are still questions about the mechanisms and structural history that require further investigation.

Salt keels in Keathley Canyon are interpreted as dominantly passively filling in the extensional gaps forms by subsalt normal faulting, which occurred shortly after allochthonous salt climbed southward. normal faults sole out onto a detachment of Oligocene age which transfer the stresses downdip to a series of compressional toe thrusts. The lithology of the Oligocene detachment strata is shale/marl content, which is geomechanically weak in strength. This weak shale/marl interval is validated by the well penetrations in Keathley Canyon area. The tilting of the basin causes the gravitational slide associated with the formation of the salt keels. Locally the keels are affected by salt evacuation of the deeper Mesozoic allochthon salt.

Allochthonous salt keels in Keathley Canyon area are a unique structural setting and have potential to create various trapping configurations for subsalt prospects. We will present BP’s observation and viewpoint of the Keathley Canyon salt keel distribution and drive mechanism. We will also provide a 2D restoration of a cross section demonstrating the mechanism and timing of Keathley Canyon salt keel formation.