This study was conducted in 2016-2017 to advance the understanding of how small-scale elements, such as texture, composition, pore-types, and diagenesis affect the rock properties of the Wolfcamp Formation. The objectives of this study were to define key rock types from thin section (petrofacies) and core (lithofacies). These facies schemes were then used to identify predictable, cyclic packages in a sequence stratigraphic framework with the goal to better understand factors controlling reservoir quality and the distribution in the Wolfcamp.
The Wolfcamp A and B have been examined in detail in two proprietary cores from the central part of the Delaware Basin. Detailed sedimentological and petrographic techniques were employed to document the different facies types and bed boundaries, their characteristics, and associated rock properties to characterize the vertical changes in facies and reservoir properties. The robustness of the sequence stratigraphic framework was enhanced with seismic, biostratigraphic, geochemical, and sedimentological data from additional available cores from Reeves, Loving, and Ward Counties in Texas.
Facies are stacked in predictive, repetitive packages that are linked to their position within a sequence stratigraphic framework. Four distinct facies associations were identified: debrite, fine-grained turbidite, calciturbidite, and distal turbidite/hemipelagic. Debrites occur above sequence boundaries and represent episodic collapse of the adjacent carbonate platform during a rise in relative sea level. Thinly bedded, fine-grained turbidites are often interbedded with replacive microcrystalline dolomite and were adeposited during interpreted low stands in relative sea level. The frequency of calciturbidites increases during interpreted high stands in relative sea level when carbonate material from the adjacent platform is shed into the basin. Basinal turbidites/hemipelagic mudstones represent the most distal, muddy tails of turbidites where silty mudstones fine-upward into hemipelagic, organic-rich, siliceous mudstones. Distal turbidites and hemipelagic mudstones have the best reservoir quality and are thickest and more abundant during maximum flooding.
The sequence stratigraphic approach improves the lateral and vertical predictability of sweet spots and the zones/areas to stay away from, which ultimately drives appraisal and development decisions. Integrating our understanding of the cyclic nature of the Wolfcamp with the calibrated e-facies derived from logs in a stratigraphic framework allows for quick high-grading of acreage away from current control points, support development planning, and new acreage evaluations.
