--> Abstract: Prospect Mars Overview, by M. J. Mahaffie, C. L. West, R. S. Barnard, and J. D. Oldroyd; #90987 (1993).

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MAHAFFIE, M. J., C. L. WEST, and R. S. BARNARD, Shell Offshore Inc., New Orleans, LA; and J. D. OLDROYD, British Petroleum Inc., Houston, TX

ABSTRACT: Prospect Mars Overview

Shell Offshore Inc., in partnership with British Petroleum Inc., has announced a discovery at Prospect Mars, located in the Mississippi Canyon Area of the Gulf of Mexico. The prospect lies in approximately 3,000 feet of water and was drilled to test a shallow amplitude anomaly (Orange) located within the gently dipping monoclinal flanks of a salt-rimmed syncline. The discovery well, drilled in 1989, penetrated 440 net feet of oil-bearing sands including six previously undetected intervals below the primary objective. Four additional appraisal wells and 3D seismic mapping have identified fourteen significant, amplitude-supported intervals (7 primary levels) ranging in depth from -10,000 to -19,000 feet. The reservoirs comprise high-quality sands with porosities of about 30% and permeab lities up to 1.5 darcies.

Most levels at Mars are trapped by a combination of structural and stratigraphic elements. Updip trap for many of the shallow reservoir levels (not deposited within the confines of bounding salt) is created by onlap/pinchout of reservoir sands onto the basin margins. Lateral trap is commonly a result of erosional truncation of the turbidite fan system. Faulting along the updip margins of the basin plays a minor role in trapping some of the less significant reservoir intervals. Trap for the deeper reservoir levels (wholly surrounded by bounding salt) is inferred to be a result of stratigraphic pinchout onto the flanking salt-cored highs. Mapped column heights in excess of 2,000 feet attest to the seal capacity of the bounding lithologies associated with the observed traps.

The sedimentary fill at Mars includes Pliocene and Miocene turbidites which onlap and overlie the bounding salt-cored highs. The reservoirs are typically sheet sands, deposited in a mid- or outer-submarine fan depositional setting. Turbidite deposition is influenced by the distribution of salt bodies which define the basin margins and control turbidite fan geometry. Sediment transport occurred through narrow entry points (sediment portals) within and between these salt masses. These portals act as focusing mechanisms for the deposition of high-energy sheet sands along the basin axis. High net-to-gross, amalgamated sheet sands are found proximal to these sediment portals, with the reservoir interval thickening to moderate net-to-gross, laterally extensive, layered sheet sands in the do nfan direction.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.