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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 66 (1982)

Issue: 9. (September)

First Page: 1424

Last Page: 1425

Title: Petrology and Reservoir Characteristics of Smackover Formation, Hatter's Pond Field--Implications for Smackover Exploration in Southwestern Alabama: ABSTRACT

Author(s): D. Joe Benson, Ernest A. Mancini

Article Type: Meeting abstract

Abstract:

Hatter's Pond field in northern Mobile County, Alabama, has produced 11 million barrels of condensate and 43 bcf of gas since its discovery in 1974. Production is from multiple-pay zones in the Upper Jurassic Norphlet and Smackover Formations. The trapping mechanism in the field is a highly complex, combination structural and stratigraphic trap involving salt movement in association with normal faulting.

The Smackover in the Hatter's Pond field area is enigmatic for the Smackover in Alabama for two principal reasons. First, the Smackover is very thin, less than 200 ft (60 m), in comparison to thicknesses on the northwest and southeast. Second, the Smackover does not show the characteristic lower Smackover-upper Smackover lithologic subdivision so apparent throughout southern Alabama and the Gulf Coast.

These unique features are a product of the field's position on the northwest flank of the Wiggins uplift. Smackover deposition was significantly affected by the uplift which maintained the Hatter's Pond area as a subaerial high while lower Smackover carbonates were being deposited in the deeper areas of the Mississippi Interior Salt basin and Conecuh embayment. It was not until near maximum transgression that the seas covered the Hatter's Pond area and deposited shallow-water upper Smackover lithologies. These lithologies were later massively dolomitized by mixing-zone dolomitization during the subsequent Buckner regression. This dolomitization almost completely masked depositional textures, but was largely responsible for the development of reservoir-grade porosity in the Hatter's Po d area.

Six major lithofacies can be identified in the Smackover in

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Hatter's Pond field: anhydritic mudstone, skeletal-peloidal packstone or grainstone, oolitic grainstone, microcrystalline dolomite, finely crystalline dolomite, and coarsely crystalline dolomite. The microcrystalline dolomite is commonly associated with bedded and nodular anhydrites and is interpreted to represent early replacement in a sabkha environment. Both the finely and coarsely crystalline dolomites are secondary in nature and represent replacement of low-energy skeletal-peloidal packstones and high-energy oolitic grainstones, respectively.

The majority of the reservoir porosity in the Smackover is late stage vuggy and/or moldic and is facies-selective and preferential to the coarsely crystalline dolomite. This porosity, which commonly ranges from 4 to 22% with permeabilities of 2 to over 100 md, is a product of mesogenetic leaching related to migration of carbon dioxide-charged fluids during the early stages of hydrocarbon maturation. The porosity is facies-selective to the coarsely crystalline dolomite, as this lithology possessed the greatest porosity and permeability at the time of migration of the carbon dioxide-charged solutions.

Evidence suggests the oolitic grainstones, which were the precursors of the coarsely crystalline dolomites, were deposited as a series of linear bars along the flanks of the Wiggins uplift. If this is the case, and more study is needed to document this definitively, the coarsely crystalline dolomite should occur in elongate mappable trends. Hydrocarbon exploration in this area and all along the flanks of the Wiggins uplift should involve location and mapping of these trends, with the greatest success occurring in areas where the trends are superimposed over structural highs produced by faulting and/or salt diapirism.

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Copyright 1997 American Association of Petroleum Geologists