The Impact of Increasing Accommodation on Sediment Deposition and Hydrocarbon Accumulation in the Greater Ship Shoal Area

Michael J. Quinn
Chevron U.S.A. Production Company, 5750 Johnston Street, Lafayette, Louisiana 70503

Published and in house proprietary eustatic sea level curves for the Gulf of Mexico indicate a subtle 2nd order sea level rise, ongoing since the Early Pliocene. During that same time many regions of the Gulf have undergone significant subsidence due to salt movement. The net result has been an increase in water depth, or accommodation space, throughout the Pliocene and Pleistocene. When sea level rise and salt movement occur in areas on the shelf where the paleo-Mississippi provided a relatively uniform sediment supply, the increase in accommodation space became a primary factor influencing the architecture of the basin fill.

In the Ship Shoal area well log suites along with regional horizon amplitude extractions were used to create conceptual depositional models for sands deposited at the 4.2, 3.0, and 1.4 Ma sequence boundaries. Together with select seismic lines this data are used to illustrate the salient features of the depositional architecture, facies, and hydrocarbon distribution resulting from changes in accommodation space.

Examples shown include large scale, sand filled, incised valley deposits coincident with the lowest accommodation setting at the 4.2 SB level, mixed channel and shoreline sands deposited as a result of increased accommodation at the 3.0 SB level and stacked aggradational shoreline and deltaic sands deposited at the highest accommodation setting at the 1.4 SB level. Discussion will also include the general impact of depositional setting on hydrocarbon accumulation.

AAPG Search and Discovery Article #90080©2005 GCAGS 55th Annual Convention, New Orleans, Louisiana