Upper Jurassic (Oxfordian) Smackover facies characterization at Little Cedar Creek Field, Conecuh County, Alabama
The Upper Jurassic (Oxfordian) Smackover Formation is a shallow-marine carbonate unit in the subsurface of the U.S. Gulf Coast, spanning from south Texas to west Florida. This field case-study focuses on Little Cedar Creek Field located in southeastern Conecuh County, Alabama. The objectives of this study are to 1) construct a 3-D depositional model for the Smackover Formation at Little Cedar Creek Field; 2) establish a sequence stratigraphic framework for the construction of the depositional model; 3) characterize and map lithofacies with high resource potential based on the depositional model; and 4) demonstrate the use of the depositional model to maximize hydrocarbon recovery in the field area Little Cedar Creek Field is located near the up-dip limit of the Smackover Formation. The top of the Smackover is found at depths between 10,000 to 12,000 feet, and the formation ranges in thickness from 60 to 120 feet. The Smackover Formation overlies the Callovian-Oxfordian Norphlet Formation and underlies the Kimmeridgian Haynesville Formation. The petroleum reservoirs in Little Cedar Creek Field, unlike most Smackover fields in the eastern Gulf region, are composed predominantly of limestone, not dolomite, and do not possess a Buckner Anhydrite top seal immediately above the reservoir. Beginning from the top of the Smackover, the facies are: (S-1) Peritidal lime mudstone-wackestone; (S-2) tidal channel conglomeratic floatstone-rudstone; (S-3) peloid-ooid shoal grainstone-packstone; (S-4) subtidal lime wackestone-mudstone; (S-5) microbially-influenced packstone-wackestone; (S-6) microbial (thrombolite) boundstone; and (S-7) transgressive lime mudstone-dolostone. Production is from both the thrombolite boundstone and shoal grainstone facies, though pressure and fluid data indicate no communication between the two reservoirs. The data indicate that the microbial communities developed on subtle topographic highs overlying the transgressive lime mudstone-dolostone in a shallow-water, low-energy, hypersaline environment, parallel to the southwest-northeast trending paleoshoreline. The Conecuh Embayment, formed by the Conecuh and Pensacola Ridges to the northwest and southeast, respectively, created low-energy, tranquil conditions that promoted the development of these opportunistic microbial organisms.