--> High-Resolution Architecture of Proximal Basin-Floor Deepwater Clastics: Examples From Outcrop, Permian Upper Brushy Canyon Formation, West Texas

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High-Resolution Architecture of Proximal Basin-Floor Deepwater Clastics: Examples From Outcrop, Permian Upper Brushy Canyon Formation, West Texas

Abstract

Well-exposed outcrop analogs of submarine fan systems are critical to the oil and gas industry. Managing complexity in conventional and unconventional deepwater reservoirs is optimized by understanding distribution of fine-scale heterogeneity, as captured in large high-resolution outcrop studies. The 35 mile continuous outcrops along the Guadalupe and Delaware Mountains expose the 1000 foot-thick Guadalupian Brushy Canyon Formation representing slope and proximal basin-floor deposits of the Lowstand Systems Tract of one third-order clastic sequence. Three informal Brushy Canyon members record vertical and lateral changes in submarine channel architecture and depocenter position. These fourth-order basin-floor fans, sourced by canyon feeder systems and deposited below an exposed shelf margin, consist of sandstones bounded by organic-rich siltstones and record cyclicity at multiple scales. This study presents detailed field mapping of the upper Brushy Canyon member (facies, event beds and sedimentary body architecture) based on centimeter-scale measured sections correlated by continuous siltstone markers mapped on high-resolution photo panels of a 4 mile-long by 350 foot-thick outcrop segment. In this detailed window, integrated with the complete Brushy Canyon system, high-resolution stratigraphic architecture documents systematic changes in facies and sedimentary bodies at multiple scales, characterizing the temporal and spatial variation in heterogeneity. Fundamental stratigraphic trends include: 1) increase in channel depth and silty-sandstone proportion; 2) more continuous channel-base mudstone drapes; 3) increase in carbonate material (shelfal allochems and mud) and TOC from marine organic matter and; 4) landward shift in depocenter. Relative sea-level change is interpreted to be the primary driver for these trends. The terminal marine deepening that flooded the shelf at the end of this 3rd-order cycle began gradually during deposition of the upper Brushy Canyon interval. Unidirectional lithological vertical trends (increasing TOC in siltstones, carbonate allochems, silty sandstone) track the longer-term base-level rise and outbuilding of the slope, while bidirectional trends in sedimentary body attributes (type, shape, size and fill style) respond to higher-frequency cyclicity. Results from this large detailed outcrop study can be applied to structured slope and proximal basin floor reservoirs, such as GoM, Brazil and West African continental margins.