ABSTRACT: Structural Development of Salt and Associated Potential Hydrocarbon Traps, Deep-Water Northern Gulf of Mexico

H. Lee Gwang, William R. Bryant, Joel S. Watkins

The continental slope of the northern Gulf of Mexico is the frontier area where recent discoveries indicate the potential for large hydrocarbon accumulations. Multichannel seismic data of the lower continental slope of Louisiana reveal that the lower slope is underlain by shallow, continuous salt. Salt in the upper lower slope originated from the deep Jurassic salt during the initial stage of salt deformation. As the salt moved to shallower depths, the downslope part of the salt moved basinward as an allochthonous nappe, evolving into massifs and ridges in the middle lower slope. Intraslope basins formed locally by withdrawal of the allochthonous salt. Lobes of salt spread further seaward forming the Sigsbee Escarpment along the base of the slope.

Various types of potential traps for hydrocarbons were created, both below and above the salt layer as a result of the intrusion of salt and subsequent withdrawal of salt. Since salt is impermeable and covers large areas, it may seal the underlying source beds. Hence, truncation of the subsalt sediment layers against the basal thrust plane of salt has the potential to trap hydrocarbons. Within the salt-withdrawal basins, hydrocarbons can escape from deep source beds along tensional faults caused by salt withdrawal or through salt-free zones caused by an evacuation of salt. Hydrocarbons can migrate into fault traps, updip pinchouts and anticlines formed by the subsidence and uplift of sediment layers associated with the withdrawal of salt.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990