The Wolfcamp Formation in the Midland Basin contains, high frequency facies variability. The dominant lithofacies include organic rich siliceous mudrocks, carbonate debrites and, turbidites. This study uses chemostratigraphic and magnetic techniques to build a sequence stratigraphic framework and measure rock fabric variability. These approaches can potentially identify crucial reservoir properties.
Ti, Zr, K, and Al, show a general transgression in the lower 260ft with superimposed higher-frequency transgressions and regressions. This portion of the unit also show consistently high degrees of bottom water restriction, based on Ni and Mo. The upper 290ft of the unit shows a regression that is punctuated by alternating zones of carbonate accumulation and clastic accumulation. This upper portion of the examined interval shows episodic alternation between well circulated and restricted bottom water conditions, with restricted conditions becoming more dominant upsection. Diagenetic processes such as chertification of sediment gravity flow facies show distinct Si/Al signatures across the core.
Anisotropy of magnetic susceptibility (AMS) quantifies the preferred orientation and intensity of magnetic grains in rocks. AMS fabrics show good correlations with certain mineralogical end members. Clay rich facies generally show planar fabrics with an overall increase in the degree of anisotropy. Such fabrics are likely caused by compaction. High inclination fabrics occur as the carbonate fraction increases. These fabrics are generally controlled by ferroan carbonate minerals and debris flows. Similarly, as the silica fraction increases, an exponential increase in fabric inclination occurs. Other near vertical fabrics are commonly associated with slumped beds and soft sediment deformation. A consistent lineation is observed across the core and could be related to compressional stress leading to layer-parallel shortening or a consistent paleocurrent direction. We are currently investigating whether fluctuating degrees of magnetic anisotropy (P') correspond to the degree of compaction. Over consolidated horizons could behave as barriers to hydrocarbon migration and behave as micro traps. Preliminary data shows a promising relationship between TOC and elevated P' values. Methods used in this study can help establish sequence stratigraphic frameworks and map fabric anisotropy which may exert strong controls on geomechanical properties and fluid migration pathways.
