Carbonate Reservoir Characterization for Identification of Stratigraphic Traps: Eastern Gulf Coastal Plain

Ernest A. Mancini¹, William C. Parcell², Wayne M. Ahr³, Victor O. Ramirez⁴, Juan C. Llinás⁵, and Milo Cameron^1
1Department of Geological Sciences, University of Alabama, Tuscaloosa, AL
²Department of Geology, Wichita State University, Wichita, KS
³Department of Geology & Geophysics, Texas A & M University, College Station, TX
⁴Ecopetrol, Bogota, Colombia
⁵Anadarko Petroleum Corporation, The Woodlands, TX

Successful development of Little Cedar Creek field in the eastern Gulf Coastal Plain is dependent on carbonate reservoir characterization. From petrographic microfacies analysis, meso- and macro-scale core description and wireline log study, six Upper Jurassic Smackover lithofacies are recognized in descending order: peritidal lime mudstone and dolomudstone to wackestone (vertical and lateral seal rock); shallow subtidal, nearshore grainstone to wackestone (upper reservoir); deeper water, subtidal lime mudstone (vertical and lateral seal rock); subtidal microbially-influenced lime mudstone to packstone (lower reservoir in the field and lateral seal rock to the northeast of the field); subtidal peloidal thrombolite boundstone (lower reservoir); and transgressive subtidal lime mudstone and dolomudstone to wackestone (lateral seal rock). The reservoirs associated with this stratigraphic trap are thrombolite boundstone and nearshore grainstone and packstone, which are underlain and overlain by lime mudstone and dolomudstone. The reservoir rocks grade into lime mudstone near the depositional updip limit of the Smackover Formation. Porosity in the shallow subtidal, nearshore, ooid, peloidal, fossiliferous grainstone and packstone reservoir is mainly dissolution moldic pores, and pore types in the sudtidal peloidal thrombolite reservoir are chiefly leached vuggy pores. These reservoirs exhibit a southwest to northeast trend through the field area. The grainstone and packstone reservoir distribution is characterized by maximum development in the central part of the field. The thrombolite reservoir is absent along the northern margin of the field and has a thickness trend characterized by local buildups in the southern part of the field area. These reservoir facies are interpreted to have accumulated in water depths of less than 3 m and within 5 km of the paleoshoreline.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas