Stratigraphy and reservoir architecture of a Permian toe-of-slope ooid fan, Happy (Spraberry) Field, Garza Co., Texas



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The Permian (Leonardian) aged Upper Spraberry Formation found in the Happy Field of Garza Co. TX, contains one of the best examples of a reservoir composed of resedimented carbonates in a deep-water slope-basin setting, with numerous whole core of wells with full suites of electric logs, high resolution 3D seismic coverage, and 20+ years worth of production data. Sequence stratrigraphic analysis from seismic data combined the lithologic analysis from outcrop analog, core, and well log data helps identify that the Happy Field is located within the transgressive systems tract of the fifth composite sequence in the Leonardian. The reservoir is composed of discrete allochthonous ooid and skeletal grains transported downslope via hyperconcentrated density flows sourced from a re-entrant in the shelf margin and deposited in a long-lived topographic depression at the toe-of-slope. Vertical heterogeneity due to layers of shaley silt punctuated by successive flows of oolitic and skeletal grains along with lateral heterogeneity created by younger flows of material create reservoir compartmentalization which can impede efficient development. Core-calibrated electric log correlations aids in the mapping of isolated compartments which helps with efficient development planning for the field.