STRATIGRAPHIC VARIABILITY OF DETRITAL CARBONATES AND ASSOCIATED PETROPHYSICAL PROPERTIES OF THE WOLFCAMP FORMATION, NORTHWEST SHELF, DELAWARE BASIN

The Wolfcamp Formation on the Northwest Shelf of the Delaware Basin is a self-sourced hydrocarbon-bearing reservoir, primarily composed of dolomitic limestone and interbedded shales. Active tectonism and high-frequency changes in sea level during the Permian influenced its reservoir quality. Multi-scale heterogeneities within the Wolfcamp are reflected in its stratigraphic architecture, petrotypes, petrophysical properties, and their spatial distribution. Thus, the Wolfcamp Formation is informally divided into four stratigraphic zones, each with different reservoir quality. Through seismically constrained reservoir modeling, relationships are established among petrotypes, petrophysical properties, and seismic attributes, to map their spatial distribution within the Wolfcamp Formation for more accurate sweet-spot targeting. The study area is west of Carlsbad, New Mexico and data include a 201 mi² (521 km²) 3D seismic survey, logs from 65 wells within the seismic survey that penetrate the entire Wolfcamp Formation, and associated production data. Petrotypes (rock types) are classified in non-cored wells using an unsupervised machine-learning technique. Total porosity, effective porosity, and water saturation logs are calculated for each well. Across the study area, the Wolfcamp dips to the southeast (SSTVD -3300 to -6100 ft [-1006 to -1860 m]; TVD ~7600 to 9100 ft [2316 to 2774 m]) and varies in thickness from ~1200 to 1600 ft (~366 to 488 m). The Wolfcamp stratigraphic framework was interpreted and represented by a detailed 3D model grid. 3D reservoir models that are constrained to the stratigraphic framework, upscaled well logs, seismic attributes, and variogram parameters illustrate the stratigraphic and proximal to distal variability of petrophysically significant reservoir rock types within the Wolfcamp Formation.