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Abstract: Field Study: Rhombochasm (Bend Conglomerate) Field, Matador Arch, Cottle County, TX

BRISTER, BRIAN S., Burnett Oil Co., Inc., Fort Worth, TX

Rhombochasm Field is a tight sand, gas/condensate reservoir discovered in mid-1994. 2-D seismic data delineated a doubly plunging (east-west oriented), anticlinal, flower structure (horst) formed during Atokan wrench-fault deformation of the northern flank of the Broken Bone graben. Graben subsidence accommodated syntectonic deposition of a Bend Conglomerate clastic alluvial fan-delta complex sourced by southerly-flowing braided streams originating from the Wichita uplift. Rapid fan deposition yielded sheets of poorly sorted muddy sandstones with discreet pebbly channel sand bodies (elongate north-south) interbedded with pebbly and coally claystones. The gas-prone carbonaceous content makes the Bend locally self-sourced. The complex structural and stratigraphic architecture of the field results in reservoir compartmentation making seismic control useful for locating development wells (both 2-D and 3-D were used).

Current spacing is 160 acres per well. Reservoir depth ranges from 7200 to 8500 feet, average net pay thickness is 75 feet and water saturation is 25%. The field is normally pressured, has an inactive downdip water leg, and an areal extent of some 2400 acres. Relatively deep burial of the muddy sediments resulted in clay diagenesis detrimental to production, thus in-situ permeability is .02 md and porosity is 11 % on average and fracture stimulations are required for economic production. From 1995 through 1997 cumulative production exceeded 5 BCF. Ultimate reserves should exceed 40 BCF. Seismically-aided stratigraphic and structural ranking of infill drilling locations, addition of pay behind pipe, refined drilling and stimulation techniques, and pipeline compression will aid future development of these reserves.

AAPG Search and Discovery Article #90936©1998 AAPG Southwest Section Meeting, Wichita Falls, Texas