Identification of Remaining Oil Resource Potential in the Frio Fluvial/Deltaic Sandstone Play, South Texas

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1994

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The Frio Fluvial/Deltaic Sandstone (Vicksburg Fault Zone) oil play of South Texas has produced nearly 1 billion stock tank barrels (BSTB) of oil, yet still contains about 1.2 BSTB of unrecovered mobile oil and an even greater amount of residual oil resources (1.5 BSTB). 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 incompletely drained and untapped reservoirs as suitable targets for near-term recovery. Interwell-scale geological facies models of Frio fluvial/deltaic reservoirs will be combined with engineering assessments and geophysical evaluations to characterize Frio fluvial/deltaic reservoir architecture, flow unit boundaries, and the controls that these characteristics exert on the location and volume of unrecovered mobile and residual oil. These results will lead directly to the identification of specific opportunities to exploit these heterogeneous reservoirs for incremental recovery by recompletion and strategic infill drilling. Reservoir attribute data were statistically analyzed from oil and gas fields throughout the geographic area covered by the Frio Fluvial/Deltaic Sandstone oil play. General reservoir attributes analyzed in detail included porosity, initial water saturation, residual oil saturation, net pay, reservoir area, and fluid characteristics. Statistical analysis of variance demonstrated no difference between oil reservoir attributes and gas reservoir attributes, indicating that oil and gas reservoirs are subsets of a larger genetically similar population. Probability functions that describe attribute frequency distributions were determined for use in risk-adjusting resource calculations. Different functions were found to be most applicable for the various petrophysical reservoir attributes.

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