WAGNER, BRUCE E., LEON DZOU, DAVID B. GRASS and ZVI SOFER, Amoco

Abstract: Petroleum System of Lower Viosca Knoll and Northeastern Mississippi Canyon, Deepwater Gulf of Mexico

The petroleum system of lower Viosca Knoll and northeastern Mississippi Canyon contains resources of ~1 billion barrel-oil-equivalents.The system covers 2075 sq km and contains ten discoveries. Elements of the system: source, reservoir, seal, traps, generation-migration and accumulation are reviewed.

Hydrocarbons were generated from Lower Cretaceous to Lower Tertiary siliciclastics. Timing and maturity are constrained by geochemical evidence and thermal maturation modeling.

Reservoir rocks are Miocene deepwater sands. Reservoirs are mildly overpressured, under-compacted and uncemented, with high permeability and porosity.

Two pressure sealing compartments exist.The first is within 600 meters of the water-bottom, the second at the boundary between Miocene overburden and the Lower Tertiary. Seal rocks are marine shales, capable of sealing hydrocarbon columns of several thousand feet. Column height and trap-size are ultimately controlled by structural spill-points.

Traps may be structural or stratigraphic. Structures are often associated with salt movement or as drape across older features.

Two elements drive hydrocarbon migration: (1) deep-cutting faults and diapiric salt connect source to reservoirs, (2) differential compaction of the source-rock section. Compaction, caused by the Miocene sediment wedge, increases formation pressure. Generation and primary accumulation of hydrocarbons exceeds sealing capacity at the deeper level, driving migration along vertical zones of weakness to shallow, low-pressure reservoirs. This is a favorable sequence of petroleum system elements and is characteristic of much of the deepwater Gulf of Mexico.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England