Facies Characterization of the Wolfcamp B and Lower Spraberry Intervals in the Midland Basin: Implications for Reservoir Quality and Distribution
Exploration of tight (unconventional) plays in the Permian Basin of West Texas has recently been a prioritized focus for the industry. A primary research topic is identifying the fundamental controls on well performance (e.g., sequence stratigraphy, geomechanics, thermal history, facies distribution, fracture development). Whilst there does not appear to be a single attribute uniquely linked to productivity, facies development and distribution appears to be one of the primary controls. Detailed facies characterization in the Wolfcamp B and Lower Spraberry intervals of two drill cores in the Midland Basin has yielded 5 main facies with distinctive physical, chemical, and biologic attributes. The main attributes for facies identification include lithology/mineralogy, texture/fabric, porosity, TOC% and depositional processes. The methodologies are primarily detailed core description, thin section petrography, QXRD, and field emission scanning electron microscopy (FE-SEM). Porosity observations are primarily based on GRI measurements and FE-SEM. Moreover, the depositional and diagenetic controls on facies development are addressed in order 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-Optimal/Fair Reservoir, Facies 2: Muddy Siltstone; Optimal Source-Optimal Reservoir, Facies 3: Silty Calcareous Mudstone; Good Source-Fair Reservoir, Facies 4: Bioclastic Wackestone/Floatstone; Fair Source-Fair Reservoir, and Facies 5: Packstone/Grainstone; Poor Source-Poor/Excellent Reservoir. Although the end-member facies can be well-delineated, main challenges are the high variability and very close intermixing of these facies for most of the lithological column, making precise landing zone positions difficult to define.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017