Mid-Continent Section

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Integrating Standard Petrophysical Analysis with Statistical Measures of Petrophysical Heterogeneity to Estimate Petrofacies in Mississippian Carbonates, North-Central Oklahoma.


Mississippian carbonate and chert reservoirs of the mid-continent are extremely complex and exhibit different scales of mineralogical, lithological, and petrophysical heterogeneity. The Mississippian interval consists of four high-frequency cycles that are capped by unconformable surfaces related to subaerial exposure. Key lithologies from core description vary from chert-brecciated limestone, bedded chert-brecciated limestone, bioturbated grainstone and mudstone, and dense, unaltered limestone. Diagenetic products including silicification, dissolution, compaction, fracturing, and brecciation are observed throughout this interval. Relationships of petrophysical methods and statistical measures of heterogeneity are explored to predict petrofacies. Initially, detailed core description, standard petrophysical analysis, and the Multi-Resolution Graph-Based Clustering method are conducted. Statistical measures of heterogeneity, including Lorenz and Dual-Lorenz Coefficient, are calculated on bulk density, neutron porosity, and sonic well logs in the Mississippian interval to evaluate which well logs best capture heterogeneity and define the optimal number of clusters needed to define the petrofacies. The results of core analysis, petrophysical analysis, and numerical measures of petrophysical heterogeneity are integrated to estimate lithofacies in non-cored wells and to identify stratigraphic cycles in order to interpret the sequence-stratigraphic framework