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Source of STACK & SCOOP Fluids: Evidence From Fluid Inclusions

Abstract

Fluid trapped in 6713 archived cuttings was analyzed from 58 wells in the STACK and SCOOP plays of the Anadarko basin in Oklahoma, applying the fluid inclusion stratigraphy (FIS) technique, fluid inclusion petrography, microthermometry, and extract GCMS. Objectives were to evaluate the vertical and lateral distribution of petroleum and correlate it to source rocks. Criteria, established to identify potential source intervals in the stratigraphic section, utilized observations from FIS character, TOC, Rock-Eval, XRF, petrographic estimates of kerogen abundance/maturity, fluid inclusion type and distribution, and maturities derived from microthermometry. Both migrated and locally generated components were distinguished, and several episodes of migration were documented within individual wells. Results indicate that the Woodford formation is the most prolific source rock basin-wide, but significant contributions can be expected from the Mississippian Springer, Chester, Caney and Meramec formations, and in some cases from the Lower Devonian Hunton formation. Locally, the Mississippian Goddard and Ordovician Sylvan and Viola formations are generative. In deeper sections of the basin, to the west, Pennsylvanian intervals are noteworthy contributors, including the Deese, Cherokee, Verdigris, Atoka and Morrow formations. In detail, the Caney formation is more significant in the south, while the Meramec and Chester formations contribute in the north. The Springer formation is more notable toward the south and west. The Woodford is anomalous throughout, but with a well-defined maturity trend of gas enrichment towards the west and a northwest to southeast band of optimal liquids generation in the center of the region. Biomarker data were collected from fluid inclusions in 13 samples in which FIS response and visible inclusion abundance is high, and contributions from indigenous kerogen can be excluded. These samples are restricted to Mississippian and Ordovician strata. The fluid inclusion extracts are similar, with main variations defined by the relative proportions of tricyclic to pentacyclic terpanes, which may reflect varying contributions from the Mississippian and Woodford. There is no evidence of significant contributions from the Sylvan or Viola in these particular extracts. Biomarker and diamondoid maturity parameters suggest early to peak oil-window maturity, and evidence of secondary cracking below 12,000 ft.