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Red Fork sandstones in the deeper part of the Anadarko basin are the downdip equivalents of fluvial and deltaic sandstones in the Cherokee Group. The sandstones have repetitive, ordered sequences of sedimentary structures in vertical section. Individual bedsets display sharp basal contacts, gradational tops, and contorted bedding. The characteristics indicate these basinal sandstones were deposited by turbidity currents.
The sandstones occur as narrow, linear constructional channels that are dip-trending. The lateral change from channel-fill to overbank facies takes place abruptly. Channel sandstones display incomplete "AE" bedsets up to 12 ft (3.6 m) thick. Overbank deposits have thin "BE," "BCE," and "CE" Bouma sequences and generally are dominated by shale.
The sandstones are very fine-grained litharenites with an average composition of 58% quartz, 8% feldspar, 17% rock fragments, 5% other grains, and 12% matrix. Cement consists mainly of calcite ranging from 2 to 40% of the bulk volume. Quartz content tends to decrease upward and matrix increases upward within bedsets. The compositional grading is accompanied by a decrease in grain size upward within bedsets, indicating deposition during a decreasing flow-regime.
Red Fork sandstones are low-permeability reservoirs with an average porosity and permeability of 7.8% and 0.1 md, respectively. Natural gas reservoirs occur mainly in the thicker, channel sequences.
The bedding character of the channel and overbank facies is reflected in gamma-ray log responses. Log characters of the two facies are used to interpret turbidite sections of uncored areas. The interpretations are adapted to the East Clinton field for prediction of constructional channel reservoirs. The interpretation of dip-trending turbidite deposits may aid in exploration and development of the Red Fork sandstones.
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