| dc.description.abstract | The Latest Artinskian to Early Kungurian Upper Wolfcamp (Skinner Ranch) Formation is exposed in the Lenox Hills of the Glass Mountains in Brewster County, Texas. These outcrops provide geoscientists and engineers a window to examine strata equivalent to the Wolfcamp A unconventional reservoirs in the southern Delaware Basin. This study provides an outcrop-based sequence stratigraphic analysis to identify distinct chemo/litho facies within a regionally correlative framework for improved reservoir characterization of organic-rich, mudrock-dominated successions. We use modern advances in Energy-Dispersive X-Ray Fluorescence (ED-XRF) chemostratigraphy to better understand depositional constraints on reservoir quantity (spatio-temporal variations) and quality (compositional, TOC richness) within a mixed carbonate-siliciclastic system.
Within the Lenox Hills, the Upper Wolfcamp Formation consists from the base up of the: 1) carbonate conglomerate-prone Decie Ranch Member,2) organic rich, mudstone-prone Poplar Tank Member, 3) mixed carbonate-siliciclastic conglomerate-prone Sullivan Peak Member, and (4) the organic poor, mudstone-prone Dugout Mountain Member. The lowermost three members of the Upper Wolfcamp Formation, especially the mudstone-prone Poplar Tank Member, were the focus of this study. Five facies were identified within the Poplar Tank Member: 1) Facies 1a (skeletal packstone/grainstone) and 1b (skeletal wackestone), Facies 2 (calcareous silty mudstone), Facies 3 (argillaceous shale/mudstone), Facies 4 (siliceous mudstone/siltstone), and Facies 5 (siliceous shale/siltstone).Within the Poplar Tank Member, the heterogeneity of the observed facies and elemental proxies throughout the lower depositional sequence of the Upper Wolfcamp Formation suggest strong depositional cyclicity. Detrital and paleo-redox proxies indicate increase in siliciclastic deposition occurred during the interpreted TST and early HST, and carbonate deposition occurring during the interpreted late TST and HST.
Comparison of reservoir quality between the Upper Wolfcamp mudstone in outcrop and core studies indicate an equivalence of strata to the informal “Wolfcamp A” reservoirs in the subsurface of the Delaware Basin. Likewise, preliminary analysis of the shale/siltstone at the base of the Dugout Mountain Member indicate a correlation to the X, Y, and Z Sands of the Wolfcamp A. These findings, coupled with complete sedimentary and geochemical analysis of the type Upper Wolfcamp (Skinner Ranch) Formation provides chronostratigraphic insights for the surface to subsurface correlations. This work indicates that to make the Wolfcamp Group in outcrop coeval to the Wolfcamp Group in the subsurface, the base of the Leonard Group (Bone Springs) should be placed at the base of the Wedin Member of the overlying Cathedral Mountain Formation. | |
