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Thin Section Analysis of a Mississippian Cored Interval for Incorporation to Reservoir and Depositional Models (McPherson County, Kansas, USA)

Abstract

Understanding the distribution and characteristics of petrophysical properties through thin section can enhance the assessment of reservoir characteristics and depositional models, as well as, providing data to improve completion and overall performance. Previously, preliminary macroscopic core and open-hole log data were collected to determine lithofacies and depositional characteristics from a Mississippian cored interval located in McPherson County, Kansas, USA. In this study, thin section observations and point count analyses were used to provide additional data for lithology, fossil presence, pore space attributes, and diagenetic history. The study interval consists of 34 feet (2,912 ft. and 2,946 ft. below KB) of Warsaw and Burlington-Keokuk (Osagean – Meramecian) formations, with thin sections taken at approximately one-foot intervals. Results show variation in mineral, fossil, porosity, and diagenetic content throughout the interval. The interval mineralogy consists mostly of calcite, dolomite, and silica-based minerals (chert, chalcedony, etc.). Lithologies range from finely crystalline dolomitic mudstones – coarse bioclastic grainstones and brecciated tripolitic chert. Fossils consist mostly of benthic organisms and are present within the lime and cherty grainstone lithologies. Multiple types of fabric and non-fabric selective porosity were observed, which include interparticle, intercrystalline, moldic, fracture, and vugs. Primary and secondary porosity have been connected and enhanced by dissolution and fracturing. Diagenetically, the interval has been subject to a complex history with most diagenetic events occurring relatively soon after deposition. Early diagenetic events such as leaching, recrystallization, dolomitization and first generation fracturuing indicate marine, meteoric, and shallow burial diagenesis. Later diagenetic changes have occurred through intermediate and deep burial events and are represented by the further dissolution of pore space, authigenic quartz (silica) replacement of calcite, styolitization, and slight presences of dedolomitization. Preliminary thin section results clarify prior macroscopic lithofacies observations and depositional characteristics and add quantitative data to descriptions. These results also help to understand discrepancies between core and well-log quantitative values. Further analysis should be conducted to ensure the proper characteristics are applied to the reservoir and depositional model.