Geologic characterization and modeling of the updip basement ridge play of the Smackover Formation in the Vocation and Appleton Field areas, southwest Alabama

The Upper Jurassic (Oxfordian) Smackover Formation is one of the most prolific oil and gas producers in the northeastern Gulf of Mexico coastal plain. In the Conecuh and Manila Sub-basins, in southwest Alabama, shallow marine carbonate deposits of the Smackover Formation accumulated on local Paleozoic crystalline basement highs, defining the Smackover updip basement ridge play. In this geologic setting, Smackover accumulation occurred in four depositional packages that are easily identifiable in well logs: (1) shallow sub-wave base level, (2) microbial reefs, (3) shoreface/shoal/lagoon, and (4) tidal flat/sabkha. The distribution of the depositional environments has been illustrated in three-dimensional geologic models for the Vocation and Appleton Field areas.; Smackover deposits have been affected by diagenetic events that have modified their petrophysical properties. Pervasive dolomitization is the most important diagenetic event from the point of view of hydrocarbon exploration. This early diagenetic process increased the permeability of rocks by connecting the pore system through the generation of intercrystalline porosity. Nonetheless, the original depositional fabric of the rock is the main control on the location of Smackover reservoirs. High quality reservoir rocks consist of thrombolite doloboundstone that identifies large microbial buildups, and ooid, oncoid dolograinstone to dolopackstone deposited in shoal and shoreface environments. A third type of reservoir is crystalline dolostone, which is primarily diagenetic in origin.; The Smackover depositional sequence occurred during a transgressive-regressive cycle. In marginal areas proximal to its updip pinchout, Smackover accumulation was the result of the complex interaction of several regional and global variables (eustasy and tectonic/thermal subsidence), in addition to local factors such as paleotopography and carbonate productivity, which is strongly related to the environmental conditions.; The exploration strategy in this oil play has to be oriented toward the location of basement structures thorough extensive gravimetric and/or magnetometric studies. The development of 3-D seismic surveys can then be focused on the identified basement paleohighs to improve the interpretation of their geometry, to determine if the Smackover Formation is completely or only partially covering the structure, and to search for the location of large microbial buildups.