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Paleoenvironmental and Diagenetic Reservoir Characterization of the Smackover Formation Jay Field, West Florida

By
Deborah M. Bliefnick
Deborah M. Bliefnick
Chevron USA P. O. Box 1635 Houston, TX 77251
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Philip A. Mariotti
Philip A. Mariotti
Chevron Geosciences 2811 Hayes Rd. Houston, TX 77082
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Published:
January 01, 1988

Abstract

The Upper Jurassic Smackover Formation in the Jay Field area, Alabama-Florida, represents an overall transgressive-regressive sequence within which several smaller lithostratigraphic units can be distinguished. The regionally extensive lower Smackover, which constitutes the transgressive phase, is characterized by limestone and dolomite mudstones to packstones with peloids and oncolites. Deposition occurred in a low energy shallow subtidal to intertidal setting. The upper Smackover, which constitutes the regressive phase, is predominantly dolomttic peloid-ooid packstones and grainstones. This reservoir facies interfingers with lower energy subtidal mudstones and wackestones. Intergranular, pore-filling anhydrite becomes common near the top of the Smackover with displacive, nodular growth occurring in some areas. The anhydrite becomes a massive nodular mosaic with minor amounts of dolomudstone near the overlying Buckner.

The Smackover dolomites formed either in a subaerially exposed supratidal setting or during early burial. The replacement is pervasive and original depositional textures are frequently obliterated. Where samples are still limestone, remnants of early marine cements can be identified which are followed by fresh water phreatic pore-filling calcite. Where mudstones and wackestones have been replaced and the dolomite is an anhedral crystal mosaic, porosity remains low. Where packstones and grainstones have been replaced and euhedral dolomite crystals have developed, intergranular and intercrystalline porosity is quite good. Subsequent to dolomitization, hydrocarbons migrated into the reservoir facies and remnants still line open pores giving the rock a black color.

Analysis of pore-throat distributions and capillary pressure curves show that the reservoir quality is a function of the original sediment type and the degree of dolomitization. Micrites range from seals when undolomitized, to intermediate in quality when extensively dotomitized. Reservoirs developed from packstone/grainstone precursors vary from intermediate in quality when slightly dolomitized to very good quality when extensively dolomitized. In general, the more extensively dolomitized the rock and the more coarsely crystalline the dolomite, the better the reservoir quality.

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SEPM Core Workshop Notes

Giant Oil and Gas Fields: A Core Workshop

Anthony J. Lomando
Anthony J. Lomando
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Paul M. Harris
Paul M. Harris
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SEPM Society for Sedimentary Geology
Volume
12
ISBN electronic:
9781565761001
Publication date:
January 01, 1988

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