Microfacies and Wireline Log Analysis of the Upper Leonardian First Bone Spring Carbonate Member, Delaware Basin, Southeast New Mexico

Allochthonous carbonate deposits in the First Bone Spring Carbonate (FBSC) interval exhibit complex architectural and compositional heterogeneity. The episodic and chaotic depositional nature of these deposits results in the development of complex stratigraphic relationships with organic-rich pelagic deposits in deep-open marine settings. In the FBSC, these organic-rich deposits are informally recognized as the Avalon and Leonard shales and are significant unconventional hydrocarbon reservoirs targeted by industry today. Bone Spring detrital carbonates have been studied previously for their potential as conventional hydrocarbon reservoirs near basin margins. However, the nature of detrital carbonate strata in the FBSC changes significantly in a deep, basin-centered setting, where such deposits not only lack potential as hydrocarbon reservoirs, but also represent geologic inhibitors to drilling and completion of horizontal wells targeting the aforementioned interbedded Avalon and Leonard shales. Considering the economic significance of emerging unconventional hydrocarbon exploration targeting FBSC member strata in deep marine, basin centered settings, further investigation of these deposits is highly relevant and of interest. In addition to the compositional, stratigraphic, and depositional heterogeneity associated with deep slope and basin FBSC deposits, diagenetic processes further increase the difficulty in accurately characterizing and predicting detrital carbonate strata within the interval. Because encountering these deposits in the lateral negatively impacts well performance and economics, understanding their compositional variation and distribution throughout the FBSC is crucial, and will facilitate new development strategies for unconventional exploration of the FBSC, not only focused on more efficient exploitation of hydrocarbons through improved drilling and completion, but also more accurate quantification of risk achieved through better understanding and increased resolution of complex FBSC strata in a deep basinal setting. Heterogeneity of the FBSC was constrained through the identification and definition of representative microfacies utilizing detailed core description, petrographic studies, and XRD data analysis. Coordination of the identified microfacies into ‘correlation associations’ facilitated the establishment of characteristic petrophysical properties and signature log responses, which in turn enables the identification and prediction of defined facies and their associated physical properties in the subsurface using commonly available, limited data sets away from core data. It was determined that heavily silicified carbonate strata are the greatest degraders to reservoir quality of a given interval and are inhibitors to drilling efficiency. The non-standard incorporation of diagenetic elements for the definition and differentiation of microfacies and correlation associations was useful for improving core-to-log correlation quality in this study. The abundant presence of originally siliceous sponge spicules and radiolarians, and greater ability for diagenetic pore fluids to permeate a deposit were identified as factors which increase silicification susceptibility of a given FBSC deposit. Empirical data gained through this research provides the framework for future studies to further improve our understanding of diagenetic processes, physical properties, and related implications associated with FBSC deposits in deep, slope and basin settings