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Abstract: Resource Optimization Through Characterization of Downdip Frio Shoreface/Shelf Reservoirs: Red Fish Bay Field, South Texas

Roger J. Barnaby, R. Ramamoorthy, M. H. Holtz

Red Fish Bay field exemplifies the tremendous bypassed hydrocarbon potential in supposedly depleted sandstone reservoirs of the downdip Frio Formation in south Texas. Prolific upper Frio oil and gas reservoirs in this field were recently abandoned in favor of deeper Frio targets. Since field discovery in 1950, more than 50 stacked lower to upper Frio reservoirs have yielded 19 MMbbl of oil and 32 bcf of gas. The trapping mechanism is an anticlinal closure on the footwall of a regional growth fault, in addition to a facies change to more shaly sediments to the east.

This study focused on delineating bypassed hydrocarbons in 19 major upper Frio reservoirs, 7300 to 8500 ft in depth, which account for 80% of the total field production. These reservoirs consist of stacked and amalgamated shoreface to inner shelf sandstones interbedded with shelf mudstones. Geological mapping and analysis of well log and production data document underexploited areas with excellent hydrocarbon saturation. Analyses of logs from recently drilled wells that targeted deeper Frio pay confirm that upper Frio hydrocarbons have been bypassed.

Conservative estimates of the remaining potential in the underexploited reservoirs indicate that 43 MMSTB (86% of the original mobile oil) and 48 bcf (80% of the original gas) remain in place. The better developed oil and gas reservoirs in this field have attained primary recovery efficiencies of 25% and 90%, respectively. Assuming these recovery factors, recommended recompletion and infill drilling strategies are expected to add 5.4 MMbbl of oil and 40 bcf of gas to the estimated ultimate recovery from Red Fish Bay field.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994