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Abstract: Sedimentology and Permeability Architecture of Atokan Valley-Fill Natural Gas Reservoirs, Boonsville Field, North-Central Texas
Mark J. Burn (1), David L. Carr (2)(*), John Stuede (3)
The Boonsville "Bend Conglomerate" gas field in Jack and Wise Counties comprises numerous thin (10-20 ft) conglomeratic sandstone reservoirs within an approximately 1,000-ft-thick section of Atokan strata. Reservoir sandstone bodies commonly overlie sequence-boundary unconformities and exhibit overall upward-fining grain-size trends. Many represent incised valley-fill deposits that accumulated during postunconformity base-level rise. This stratal architecture is repeated at several levels throughout the Bend Conglomerate, suggesting that sediment accumulation occurred in a moderate- to low-accommodation setting and that base level fluctuated frequently.
The reservoir units were deposited by low-sinuosity fluvial processes, causing a hierarchy of bed forms and grain-avalanche bar-front processes to produce complex grain-size variations. Permeability distribution is primarily controlled by depositional factors but may also be affected by secondary porosity created by the selective dissolution of chert clasts. High-permeability zones (-2.8 darcys) are characterized by macroscopic vugs composed of clast-shaped moldic voids (-5 mm in diameter). Tight (low-permeability) zones are heavily cemented by silica, calcite, dolomite, and ankerite and siderite cements.
Minipermeameter, x-radiograph, and petrographic studies and facies analysis conducted on cores from two Bend Conglomerate reservoirs (Threshold Development Company, I. G. Yates 33, and OXY U.S.A. Sealy "C" 2) illustrate the hierarchy of sedimentological and diagenetic controls on permeability architecture.
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ACKNOWLEDGMENTS AND ASSOCIATED FOOTNOTES
(1) Bureau of Economic Geology, The University of Texas at Austin, Austin, TX 78713 (Current address: 11A Mayfair Place, New Plymouth 4601, New Zealand)
(2) Bureau of Economic Geology, The University of Texas at Austin, Austin, TX 78713
(3) Scientific Measurement Systems, Inc., 2209 Donley Dr., Austin, TX 78758
(*) Denotes speaker other than senior author.
Copyright © 1999 by The Gulf Coast Association of Geological Societies