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