ABSTRACT: Sequence Stratigraphy as Key to Evolution of Hydrocarbon Prospects; Examples from Northern Gulf of Mexico

Allen Lowrie, Neil H. Sullivan

Sequence stratigraphy is the study of rock relationships within a chronostratigraphic framework. Sequence stratigraphy is a guide to hydrocarbon prospect description and prediction. An individual sequence is a conformable succession of related strata bounded by major unconformities and corresponds to a 3rd order cycle, generally with a periodicity of a million or so years.

Within a sequence are parasequences, conformable successions of related beds or bed-sets bounded by unconformities and corresponding to a 4th order cycle, with a periodicity ranging from 20 k to 100 k years. Their physical reality is based on Milankovitch climate cycles. As used here, the lateral distribution of strata and bed is global.

In the northern Gulf of Mexico, an individual prospect probably formed over a period of 10⁵ years. A hydrocarbon play, such as the Flexure Trend, evolved over a period of 10⁶ to 10⁷ years.

A compilation of potential hydrocarbon trap types has been assembled for the Louisiana offshore, from coastal plain to lower slope. These potential traps are listed according to paleophysiographic provinces: coastal plain, shelf, shelf-break, upper slope, middle slope, and lower slope.

Characteristics of each trap type are tabulated. The characteristics include: tectonics, regional and local sedimentation rates and types, position within an evolving sequence as determined by sequence stratigraphy, duration of reservoir and/or trap creation, and sea-level position. Regional geologic processes, such as salt tectonics, and approximate rates at which they operate are also listed.

Exploration designations such as hydrocarbon province, play, and prospect may be correlated with continental margin wedge, sequence (strata), and parasequence (bed), respectively.

AAPG Search and Discovery Article #90999©1990 GCAGS and Gulf Coast Section SEPM Meeting, Lafayette, Louisiana, October 17-19, 1990