Abstract: Gulf Coast Cenozoic-Model for Application of Stratigraphic Concepts to Exploration on Passive Margins

By

Doris Malkin Curtis and Edward B. Picou, Jr.

Since the early examination of rotary drill cuttings in the 1920s and the acceptance of electric and geophysical methods as geologic tools in the 1930s, the application of data derived from direct observation (fossils and rocks) to interpretation of data from indirect observation (electric and geophysical surveys) has resulted in the discovery of more than 40 billion bbl of oil and 300 Tcf of gas in the Gulf Coast Cenozoic section. With basic stratigraphic principles and sophisticated exploration technology, still more petroleum remains to be found.

The lithologically monotonous sequence of more than 50,000 ft (15 km) of Cenozoic shales and sandstones was deposited in varied depositional settings from continental to bathyal marine. Studies of modern-sedimentation models and ancient-sediment distribution patterns, and of the Cenozoic microfaunal succession, ecology and paleoecology, have formed the basis for concepts that have evolved during the past 50 years. These include: (1) there is a close interrelation in time and space of environment, sedimentation, fauna, structure, and hydrocarbon distribution; (2) in the generally regressive basin-filling cyclic sequence, gross lithologic units are diachronic; (3) benthonic-foraminiferal zonation provides isochrons and paleoenvironmental indicators; (4) within each cycle, deltaic depocenters can be recognized; (5) elements of deltaic and littoral morphology can be interpreted from depositional sequences; (6) facies distribution is the product of rate of supply of sediments, rate of subsidence of the basin, and energy distribution in the depositional environment; (7) distribution of sandstone reservoirs is predictable from biofacies and lithofacies studies.

Concepts can be applied to such problems as electric-log correlations, correlating across growth faults, determining base of objective section, calibrating seismic events, well-design programs for geopressured drilling, salt-dome exploitation, not only in the search for new reserves in the Gulf basin but also in the exploration of other paralic basins with similar clastic fill on passive continental margins.

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