The Role of Burial History in Determining Hydrocarbon Systems in the Deepwater United States Gulf of Mexico

G. M. Apps, J. C. Mutschler, C. L. Blankenship, R. L. Boyce, K. P. Boyd, D. S. Brumfield, B. Chambers, F. J. Peel, N. Piggott, C. J. Travis, B. Yilmaz

In the deepwater northern Gulf of Mexico burial history controls all aspects of the hydrocarbon system: reservoir and seal presence; hydrocarbon generation and migration; trap presence and seal integrity. In many parts of the world, structures are produced by tectonic processes; thus trap generation and trap integrity are independent of burial history. This contrasts with the Tertiary Gulf, where structures were gravity driven by sediment loading and topographic gradients. In addition, the Plio-Pleistocene sediments were deposited rapidly, generating significant overpressure, which limits seal effectiveness.

Burial history in the Gulf has two components: sediment load and salt (emplacement, followed by withdrawal). The distribution of sediment and salt vary in a systematic manner across the Gulf, thus defining a number of distinct hydrocarbon systems.

At any one time, much of the basin was starved of sediment while selected areas were over supplied. An understanding of the geographic distribution of the Tertiary depocenters through time allows the explorer to develop predictive models for all aspects of the hydrocarbon system:

- The center of each depocenter, with high sedimentation rates, contains the best reservoirs.

- The source rocks are matured by the sediment load; the timing of trap generation relative to hydrocarbon maturation determines the likelihood and phase of charge.

- Supra-salt prospectivity relies on charge post-dating salt weld formation, since salt canopies lie between the trap and the source rock. The age and thickness of the sediment load determine the timing of salt welding.

- Salt withdrawal processes dominate structures in the deepwater. This results in a high density of structures, with the size of potential traps depending on a number of factors, including the thickness of salt and overlying sediment. Trap integrity is primarily controlled by recent sedimentation rates.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995