Undiscovered Hydrocarbon Plays for the Gulf of Mexico
Authors: Lowrie A. , Moffett S. , Meeks P. , Lerche I. , Adams R. 
Published: October 2008

The salt-flood basin concept provides a detailed model for deepening (via subsidence) and basinward migration of salt along tbe northern Gulf of Mexico. Paleotectonic restorations, with salt unrestored, reveal a paleo-Sigsbee salt wedge beneath the Upper Jurassic to Pieistocene continental slope. This has been a "permanent" feature of the prograding margin, a salt-sediment geometry unaccounted for in existing salt-tectonic theories.

A permanent, migrating "salt nose" provides an obstacle against which gravity-driven sediments are deposited. Some effects of this may include (1) creation of reservoirs (2) provision of heat (via conduction) for thermal maturation (3) development of sediment compression zones where fractures are generated as Mohr's criteria of failure is exceeded and (4) the possibility of inversion tectonics (a shift from extensional to compressive forces). The result is a paradigm where sediments, salt, and basement tectonic forces act individually and/or synergistically. This includes tectonies above saft and between salt and basement. Basement roughness, influenced by paleo-fracture zones, may impact overlying salt and sediments.

Several intriguing tectonic scenarios might occur (1)migrating salt rhat overrides a stationary basement may set up a right-lateral stress couple as viewed from the west. The surface extension of the resultant right-lateral stress coincides with the intersection between salt and the sea flow (2) differential compaction of pelagic sediments draped over basement highs can result in ring and radial fracturing until the area is drowned by coarser turbidities. This may create an undiscovered hydrocarbon reservoir. Advancing salt could decapitate the reservoir, resulting in hydrocarbon liberation (3) pressure compartments, dependent on stress-couples and regional deposition, may exist beneath the salt.

Introduction

Using the latest geologic data along north-to-south cross-sections of the Gulf of Mexico (Salvador, 1991) and then employing classical back-stripping techniques, a novei view of the Gulf's evolution emerges (Lowrie, et al., 1996) (Fig. 1). No attempt was made to model the possible behavior of the plastic salt; rather, the emphasis was on back-stripping known sedimentary formations and allowing salt to reside where the removed formations permitted. It is not known whether the overall Louann Salt movement has been predominantly vertical or horizontal, or a combination of the two; and also unknown is the origin of the Louann Salt (Lowrie, et al., 1996). Given such unknowns, it was geologically reasonable to assign present Holocene shelf-slope-Sigsbee Escarpment-continental rise bathymmtry to each succeedingly older paleotectonic restoration (Fig. 1).

Implications of the required constancy of shelf and slope bathymetry are that there is a "permanent" salt nose to the prograding wedge. The salt nose provides bathymetric highs against which gravity-driven, mass-wasted sediments may be deposrted (Lowrie, 1994) creating reservoirs and the highly thermally conductive salt causes thermal anomalies. Conclusions drawn show the unrestored salt migrating into the Guff of Mexico basin as it continues to subside. Additional salt may be provided by salt-filled, failed rifts (analogous to salt-infilled Afar Traingle) (idea in Salvador, 1991) or from interpreted saft overlying basement (Hall, 1996).