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Sequence Stratigraphic Setting and Reservoir Compartmentalization of Leonardian Oolitic Basin-Floor Fan Complexes, Midland Basin, TX

Jason L. Clayton
Jackson School of Geosciences University of Texas at Austin [email protected]

     The Happy Spraberry Field is a Leonardian- toe-of-slope reservoir located in the northeastern corner of the Midland Basin. A dataset composed of 15 cored wells totaling 400 m of section, over 400 km2 of high-quality 3D seismic, 300 well logs, and extensive engineering data, makes Happy one of the best sampled deepwater carbonate reservoirs in the Permian Basin and perhaps the world. This dataset shows that complex stages of deposition and erosion create strong internal compartmentalization and a distinct discontinuous along-strike exploration play.
     The reservoir interval is located within an early transgressive systems tract of the 4th or 5th composite sequence of the Leonardian stage of the Permian. The main reservoir facies is massive skeletal-peloidal-oolitic grainstone deposited by hyperconcentrated turbidity flows. Skeletal-peloidal packstones and reef-margin-derived megabreccia/ debris flows are subordinate reservoir facies. The most volumetrically abundant facies is mm-laminated/ rippled mixed siliciclastic turbidites with common soft sediment deformation. A hemipelagic silty shale forms the top seal and base of the reservoir interval.
     Seismic and well-log-based cross sections document the complex mounded geometry of stacked ooid grainstones cut by younger siltstone- and megabreccia-filled channels. This oolitic basin-floor fan accumulated preferentially within a paleotopographic low, with the thickest areas often corresponding to the younger fan-dissecting channels.
     The general sequence of events includes: shelf margin failure, deposition of megabreccias in paleo-topographic lows along the slope, ooid shoal formation in the re-entrant of the shelf margin and transport downslope on top of the previously deposited megabreccias, then later dissection by younger turbidites and debris flows.


AAPG Search and Discovery Article #90070 © 2007 AAPG Foundation Grants in Aid