Abstract
The Midland Basin Wolfcamp formation of upper Pennsylvanian through lower Leonardian age, has experienced a substantial increase in both vertical and horizontal activity in the past five years. The Wolfcamp formation is regionally extensive within the Midland basin and is composed of four subunits; Wolfcamp A, B, C and D (lower Wolfcamp through upper Wolfcamp). Multiple interfingering depositional environments are observed causing for complex, high-frequency lithologic variation within individual stratigraphic sections. These varying forms of sediment distribution are directly linked with proximity to the major carbonate production centers in the region, the Central Basin Platform and the Eastern Shelf. Litho-facies can range from mega-breccia proximal to the central basin platform to sediment gravity flows that reach out into the axis of the basin. Variable physical mechanisms of sediment dispersal due to differing environments of deposition lead to fundamentally unique sets of complexly stacked lithofacies. It is this heterogeneity that makes the identification of horizontal landing zones difficult based solely on conventional wireline logging methods. High-resolution XRF chemostratigraphic methods are herein documented to improve landing zones for horizontal wells.
In order to account for this lithologic heterogeneity, X-Ray Fluorescence (XRF) chemostratigraphy was employed to help identify potential landing zones through major and trace element analyses. Redox sensitive trace metal abundances of Mo, Ni, U, V, Se, and Cu can be used to infer intervals of increased preservation potential within the core using high resolution (2-inch) spacing on core analysis. Not only can the trace elements shed light into the levels of oxygenation at the sediment/water interface, but can also provide insight into the mineralogical variations along the horizontal well bore providing additional data to contribute to more accurate engineered fracturing designs. These measurements along the lateral are conducted on cuttings and run through a bench top XRF onsite for rapid understanding of changing conditions. Identifying favorable landing zones has been demonstrated to increase EURs in multiple wells, and future work will focus on deploying XRF based chemostratigraphy to further refine landing zones throughout the Midland basin, and lower overall well costs.
