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Sequence Stratigraphic Model and Depositional Setting of The Permian Wolfcamp Tight Oil Play: Linking the Delaware and Midland Basins Through a Unified Stratigraphic Framework


Historically industry has approached unconventional reservoirs, such as those in the Permian, as a “statistical” play that lacks spatial predictability of reservoir characteristics. However, a recent focus on differentiating reservoir properties within the Wolfcamp interval resulted in development of an integrated sequence stratigraphic framework through detailed observations from log data, seismic, core, high definition image logs, and log based mineralogy models which predicts depositional trends throughout the Delaware and Midland basins. The stratigraphic framework recognizes 2 composite sequences, composed of clastic-rich Lowstand (LSS), carbonate-rich Transgressive (TSS), and mixed clastic-carbonate Highstand (HSS) Sequence-Sets respectively, and can be used to predict facies and mineral trends throughout the greater Permian Basin. The basal composite sequence is represented by the Lower Wolfcamp, and is dominated by mudstone-rich strata with varying contributions of carbonates depending on the sequence stratigraphic interval. The Lower Wolfcamp (lithostratigraphic relation to Wolfcamp C and D) represents a humid climate with intense chemical weathering of the continent, as clay-dominated sediment is transported from northerly and southerly point sources. The Upper Wolfcamp system represents a separate composite sequence, and reflects a dramatic shift from humid climate to arid climate regime. This composite sequence overlies a 2nd order sequence boundary and correlative conformity in the basin and shows a well-defined clastic-rich LSS (lithostratigraphic relation to Wolfcamp B) reflecting a northerly sediment source with minimal contributions from the south. Up section, carbonates dominate the TSS (lithostratigraphic relation lower Wolfcamp A) where major slumps, debris flows, turbidites, and pelagites can be mapped in a predictable depositional model. The top of the TSS has been mapped as a regional Maximum Flooding Surface (mfs), representing the most landward position of the shoreline and optimal carbonate production and delivery to the basin. The HSS (lithostratigraphic relation upper Wolfcamp A) shows a mixed carbonate-clastic system dominated by submarine fan complexes can be mapped regional and indicates a source of sediment from the North. This framework demonstrates the predictable power of sequence stratigraphy in unconventional assets, particularly deepwater deposits that record a more complete record of deposition than the shelfal setting. The sequence stratigraphic framework provides excellent perspective for regional opportunity identification and helps to fill interpretive gaps when comprehensive formation evaluation data is not available.