Revitalizing a Mature Oil Play: Strategies for Finding and Producing Unrecovered Oil in Frio Fluvial-Deltaic Sandstone Reservoirs of South Texas

The Frio Fluvial-Deltaic Sandstone (Vicksburg Fault Zone) oil play of South Texas has produced nearly 1 billion barrels (Bbbl) of oil, yet it still contains about 1.6 Bbbl of unrecovered mobile oil and nearly the same amount of residual oil resources. More than half of the reservoirs in this depositionally complex play have been abandoned, and large volumes of oil may remain unproduced unless advanced characterization techniques are applied to define untapped, incompletely drained, and new pool reservoirs as suitable targets for near-term recovery. Interwell-scale geological facies models of Frio fluvial-deltaic reservoirs are being combined with engineering assessments and geophysical evaluations in order to characterize reservoir architecture and flow-unit boundaries and to determine the controls that these characteristics exert on the location and volume of unrecovered mobile and residual oil. These results will help identify specific opportunities to exploit these heterogeneous reservoirs for incremental recovery by recompletion and strategic infill drilling. Progress during the third project year centered on technology transfer activities. The reserve-growth potential of reservoirs in two fields within the play, Rincon field in Starr County and Tijerina-Canales-Blucher field in Jim Wells County, was documented in a Topical Report published by DOE and in this report. Specific opportunities to exploit untapped and incompletely drained compartments were identified. Results of this effort were also presented at both local and national technical meetings and in two courses hosted by related programs. Preparations have begun for two workshops centered around the activities of this project, as well as the construction of a microcomputer-based Geologic Reservoir Characterization Advisor (GRCA). The short courses, scheduled for April and June 1996, along with the GRCA, will demonstrate for operators of this mature play the potential that remains in reservoirs threatened by premature abandonment and will document methods for locating and efficiently recovering the tremendous remaining resource. The integrated multidisciplinary characterization methodology demonstrated in this project is applicable to reservoirs throughout the Frio Fluvial-Deltaic Sandstone play, to other fluvial-deltaic plays within the Gulf Coast, and more broadly to any mature fluvial-deltaic play in the United States.