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One of the major problems encountered during exploration for hydrocarbons in the Smackover in southwestern Alabama is delineation of porosity trends within the unit. Unlike Smackover reservoirs in Arkansas, Louisiana, and Mississippi, which are dominated by primary interparticulate porosity, much of the porosity in the Smackover in southwestern Alabama is secondary in nature and does not correlate with primary depositional features. Smackover reservoirs in southwestern Alabama can be divided into 3 general classes: interparticulate-moldic reservoirs, dolomitic intercrystalline reservoirs, and vuggy reservoirs. Interparticulate-moldic reservoirs occur in a narrow band that parallels and lies 10-20 mi downdip of the updip limit of the Smackover. Porosity consists of small a ounts of interparticulate and moderate amounts of oomoldic or pelmoldic porosity. Interparticulate-moldic reservoirs are characterized by moderate to high porosities (10-20%) but relatively low permeabilities (5-10 md) unless the lithology is dolomitized. Moldic porosity is also associated with large amounts of microporosity, which can significantly affect water saturation. Intercrystalline dolomite reservoirs are common along the updip limit of the Smackover and across several prominent paleohighs such as the Conecuh Ridge and the Wiggins arch. Reservoirs possessing only intercrystalline porosity have highly variable permeability but low porosity (6-8%) and are rarely productive unless fractured or leached to produce vuggy porosity. Vuggy reservoirs are common across paleohighs or along the updip margin. They are characterized by good porosity (10-20%) and permeability (10-100 md), but also possess large amounts of microporosity.
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