| dc.description.abstract | The “Wolfberry” play, which is made up of the Spraberry and Wolfcamp formations, is an important resource for the exploitation of hydrocarbons with a need for additional petrophysical understanding. Although the Wolfcamp is categorized as a shale, it is a complex and heterogeneous formation composed of multiple facies. The unique lithological composition of each facies controls formation properties, which further drive reservoir/source quality. With the integrated laboratory- and field-scale analyses, this study uses mostly laboratory petrophysical evaluation to gain insight on the relationship between facies and reservoir/source quality in the Lower Spraberry and Wolfcamp intervals throughout the Midland Basin. To achieve this objective, 48 core plugs taken from three wells evenly spaced in the Basin, that represent different facies end members in several of the Lower Spraberry and Wolfcamp intervals, are evaluated. In order to evaluate the Wolfberry formations, vacuum-assisted fluid immersion porosimetry (FIP), fluid displacement, fluid imbibition, total organic carbon (TOC), pyrolysis, X-ray diffraction (XRD), contact angle, and mercury intrusion porosimetry (MIP) tests were used to investigate petrophysical properties such as porosity, geochemistry, mineral composition, wettability, permeability, and tortuosity. Facies were divided into three groups of depositional environments for comparison: lowstand channel fan complex and windblown deposited siliceous/clay rich lithotypes, highstand/lowstand reef carbonate gravity flow deposited packstones and grainstones, and highstand deep-water hemipelagic and distal turbidity current deposited carbonate mudstones. From the petrophysical and geochemical results of this study, it was determined that the Lower Spraberry and Wolfcamp intervals are primarily oil-wet to intermediate-wet, and both reservoir quality and source potential increase as the carbonate content decreases, and they are the highest in the siliceous- and clay-rich facies (porosity 2.0-10.2% and TOC 3.0-3.5 wt%). However, the packstone and grainstone facies in the Wolfcamp B stratigraphic unit tends to develop a high secondary porosity (7.8-8.5%) associated with the dissolution vugs, and the carbonate mudstone facies in all units often has a high secondary porosity (2.4-8.1%) from fracturing. Furthermore, the well logs corroborate the heterogeneity of the Wolfcamp intervals. These laboratory-scale test results tied to the well logs and paired with similar studies make an investigation on a broader basin scale possible. | |
