Upper Jurassic updip stratigraphic trap and associated Smackover microbial and nearshore carbonate facies, eastern Gulf coastal plain

Abstract

The development of Little Cedar Creek field in the eastern Gulf coastal plain of the United States has shown that the current exploration strategy used to find hydrocarbon-productive microbial and high-energy, nearshore carbonate facies in the Upper Jurassic Smackover Formation requires refinement to increase the probability of identifying and delineating these potential reservoir facies. In this field, the petroleum trap is a stratigraphic trap characterized by microbial boundstone and packstone and nearshore grainstone and packstone reservoirs that are underlain and overlain by lime mudstone and dolomudstone to wackestone and that grade into lime mudstone and dolomudstone near the depositional updip limit of the Smackover Formation. Reservoir rocks trend from southwest to northeast in the field area. The grainstone and packstone reservoir is thickest in the central part of the field. The boundstone reservoir is thickest in local buildups that are composed of thrombolites in the southern part of the field and is absent along the northern margin. These reservoir facies are interpreted to have accumulated in water depths of approximately 3 m (10 ft) and in 5 km (3 mi) of the paleoshoreline. In contrast to most other thrombolites identified in the Gulf coastal plain, these buildups did not grow directly on paleohighs associated with Paleozoic crystalline rocks. The characterization and modeling of the petroleum trap and reservoirs at Little Cedar Creek field provide new information for use in the formulation of strategies for exploration of other Upper Jurassic hydrocarbon productive microbial and related facies associated with stratigraphic traps in the Gulf coastal plain.