The petroleum system of the western Atwater fold belt in the ultra-deep water Gulf of Mexico

Moore, M.G., Gillian Apps, and Frank Peel, BHP Petroleum (Americas) Inc, Houston, TX

Abstract

Recent major discoveries at Mad Dog, Atlantis, and Neptune have demonstrated the potential of the western Atwater fold belt in the ultra-deep water (> 5000’) Gulf of Mexico. Understanding the nature and scale of the petroleum system is important in determining an appraisal strategy for the discoveries and for pursuing other exploration opportunities.

Much of the topography caused by early salt pillowing was filled in by the time the middle and lower Miocene reservoir rocks were deposited. Compression occurred in the upper Miocene and Pliocene forming the structural traps. The three most common trap types were large faulted anticlines, salt pillows, and thrust-faulted structures.

The reservoir rocks in the western Atwater fold belt are middle and lower Miocene submarine fan systems deposited near the base of slope. The systems appear to be larger than the individual prospect size. The location of the younger depositional systems are influenced by the topography left behind by the older systems.

Deposition of a thick Pleistocene section led to a late charge that migrated into the structural traps. The source rock for the western Atwater fold belt is thought to be Upper Jurassic and Lower Cretaceous carbonates and marls. Hydrocarbon, generated from the source rock, migrates vertically or up faults until it reaches a carrier bed. It then moves up structure along the carrier bed into the traps. Miocene shales seal the hydrocarbon in the reservoir.