Heather E. Fowler1
(1) University of Alabama, Tuscaloosa, AL
Abstract: Characterization of the Smackover Reservoir: Chatom Field, Washington County, Alabama
Chatom Field is located in west central Washington County, Alabama and is situated over a salt anticline. The Upper Jurassic Smackover Formation is the producing unit in the field. In the Chatom Field area, the Smackover can be divided into lower, middle, and upper intervals. Peloidal wackestone/packstones and peloidal, oncoidal, and oolitic grainstones and packstones comprise the upper unit. The middle unit, the "brown dense" is comprised of peloidal wackestone interlaminated with mudstone. The lower unit is an algal-laminated mudstone and a peloidal and oncoidal wackestone/packstone.
Reservoir grade rock at Chatom Field occurs in shoal grainstones and packstones in the upper interval. The upper seal is the Buckner Anhydrite, which includes both sabkha and subaqueous anhydrites. Organic mudstones in the "brown dense" and the lower Smackover mudstones are the hydrocarbon source rock. Three distinct grainstone/packstone shoal intervals comprise the multiple reservoirs of the Upper Smackover.
Porosity and permeability values for the shoal intervals vary. Shoal 1 has an average porosity of 9.15 millidarcies and an average porosity is 18.39 %. Shoal 2 has an average permeability of 11.6 millidarcies, with an average porosity of 21.35 %. Shoal 3 has an average permeability of 15.73 millidarcies, and an average porosity of 23.13 %. The variation in porosity and permeability is indicative of the role that diagenesis has played in reservoir development. Multiple reservoir intervals within the upper Smackover are heterogeneous with several pore types. Moldic porosity is the most common pore type with lesser amounts of interparticulate and vuggy porosity, and minor intraparticulate porosity. Understanding and tracking variations in permeability and porosity within the shoal intervals is essential for maximizing the recovery of hydrocarbons. With production significantly decreasing, Chatom Field is ideal for the application new technologies, which will aid in enhancing total hydrocarbon recovery.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana