Geologic Controls on the Distribution of Oil and Gas Fields In Neogene Strata of the Gulf Coast, U.S.A

A study of the geologic controls on undiscovered conventional oil and gas resources in Neogene strata of the onshore coastal plain and State waters of the Gulf Coast of the United States included evaluations of: (1) hydrocarbon source rocks (source-rock maturation, hydrocarbon generation and migration), (2) reservoir rocks (sequence stratigraphy and petrophysical properties), and (3) hydrocarbon traps (trap formation, timing, and seals). Principal factors controlling the distribution of both known and undiscovered fields include the distribution of paleo-drainage systems, pre-existing shelf margins, salt-related structures, minibasins, top of the overpressured zone, and climate-influenced eustatic sea level fluctuations. Components of the study included well-log cross sections, sequence stratigraphy, reservoir quality, existing production data, field-size distributions, analogs in offshore federal waters, source rock and thermal modeling, seismic interpretation, and structural modeling. Sequence stratigraphic interpretations, coupled with geophysical studies of overpressured reservoirs and geochemical studies of hydrocarbons and source rocks, indicate that known oil and gas fields reside primarily in highstand and transgressive systems tracts in clastic reservoirs deposited on continental shelves and shelf-margin deltas. In contrast, the majority of undiscovered conventional oil and gas resources are thought to reside in stratigraphically deeper clastic reservoirs that were deposited primarily in slope fans and basin-floor fans that formed as low-stand systems tracts in response to episodic fluctuations of sea level.