Evaluating the depositional environment, lithofacies variation, and diagenetic processes of the Wolfcamp B and lower Spraberry intervals in the Midland Basin: Implications for reservoir quality and distribution

Detailed facies characterization in the Wolfcamp B and lower Spraberry intervals of two drill cores in the Midland Basin has yielded 5 main lithofacies with distinctive physical, chemical, and biologic attributes. The main attributes for facies identification include lithology/mineralogy, texture/fabric, porosity, hydrogen index, and total organic carbon (TOC) content. The methodologies are focused on detailed core description, thin-section petrography, quantitative X-ray diffraction (QXRD), and field emission scanning electron microscopy (FE-SEM). Porosity data are primarily based on GRI (Corelab) measurements and FE-SEM assessment. Moreover, the depositional and diagenetic controls on facies development are addressed to assess the dominant geological processes that govern reservoir quality and distribution. A five end-member facies model is proposed to characterize source and reservoir elements through delineating facies tracts. The five end-member facies are: facies 1: silty mudstone; optimal source and optimal to fair reservoir, facies 2: muddy siltstone; optimal source and optimal reservoir, facies 3: silty calcareous mudstone; good source and good reservoir, facies 4: bioclastic wackestone-floatstone; fair source and fair reservoir, and facies 5: packstone-grainstone; poor source and poor to excellent reservoir. The proposed facies scheme aims to provide a more comprehensive approach to capture the high vertical and lateral variability in this mixed carbonate and fine-grained clastic succession. Through this detailed textural, compositional, sedimentologic, and diagenetic approach, this facies model can be used to better understand reservoir quality and distribution throughout the Midland Basin.