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The AAPG/Datapages Combined Publications Database

Oklahoma City Geological Society

Abstract


The Shale Shaker Digest IX, Volumes XXVII-XXIX (1976-1979)
Pages 192-210

Distribution, Depositional Environment, and Reservoir Properties of the Pennsylvanian Cottage Grove Sandstone, South Gage Field, Oklahoma

Danny Joe Towns

ABSTRACT

The Pennsylvanian Cottage Grove Sandstone in the Ochelata Group of the Missourian Series produces oil and gas in the South Gage field, a stratigraphic trap in central Ellis County, Oklahoma. The Cottage Grove Sandstone is interpreted as an offshore shallow-marine bar.

Sandstone development occurred as a convex-upward sand buildup. The body is enclosed within marine shale; lower and lateral contacts are quite sharp, whereas the upper contact is rather gradational. The sandstone body extends for more than 11 miles and averages approximately 2 miles in width. Maximum sandstone thickness exceeds 100 feet.

Sedimentary structures within the unit include (1) a lower zone of small-scale cross-stratification, (2) an intensely burrowed zone, and (3) an upper zone of siltstone-shale interstratification. Due to its coarser grain size (very fine sand), the small-scale cross-stratified zone is the only oil-productive zone in the Cottage Grove. Massive bedding is present in thin, carbonate-cemented layers.

Regional correlation of the Cottage Grove northward indicates that a sharp break in the depositional slope did not exist between limestone deposition to the north and terrigenous clastic deposition to the south. Correspondingly, it is thought that fairly shallow water conditions existed at South Gage during Cottage Grove deposition. Carbonate constituents probably were derived from this northern carbonate region, but terrigenous clastics of the Cottage Grove were transported into the area from the east; they probably were derived to a large extent from the Ouachita uplift. The South Gage field was more than 20 miles west of the eastern coast and 40 miles south of carbonate deposition.

Fine grain size and abundance of various types of diagenetic clays (illite, kaolinite, and chlorite) are responsible for high water saturations measured in core analyses and calculated from log analyses. They also may create problems in well completion and development of the field. Oil recovery depends primarily upon pore-throat and average pore sizes, which relate both to the grain size and diagenetic products. The thin, carbonate-cemented layers may serve as barriers to fluid migration.


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