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Petrophysical and Paleo-environmental Assessment of a Mississippian Rock Interval from Central Kansas, (Mid Continent-US) Using Thin Sections

Abstract

The Mississippian rocks (Osagean-Meramecian) have received attention as a proven hydrocarbon reservoir due to their distinctive petrophysical characteristics and hydrocarbon potential in several studies. However, in central Kansas, although previous studies have provided information about the regional geologic and structural characteristics of the Mississippian rock interval, fewer studies have specifically focused on petrophysical properties and their relation to paleo-environmental conditions during deposition. This study aims to provide additional information on the petrophysical characteristics and the paleo-environmental conditions during which the Mississippian rock interval was deposited. The objective is to evaluate the porosity, permeability, mineralogy, and grain textures and distribution from a Mississippian age core interval and to determine characteristics rock facies of the interval. Core, thin sections, and well logs from the study interval was obtained between -1379ft. and -1,409 ft. (MSL). Quantitative and qualitative methods were used to collect data from the cored interval to describe the lithofacies, assess the depositional environment, and determine diagenetic history. The two major lithofacies identified are tripolitic chert (TC), which is dominantly silica, and dolomitic mudstone (DM), which consists of dolomite and clays. The TC is a well-cemented crystalline facies with rounded to angular clasts and contains microfossils that are partially or completely filled with silica. The DM is characterized by a muddy (clays) to grainy (dolomite) fabrics. Visible grains in the DM consist of rounded to sub-angular clasts. The depositional environment is interpreted as a shallow, warm, inner to middle carbonate ramp environment. Diagenetic events such as recrystallization, dolomitization, leaching and fracturing, visible in the samples and thin section likely indicate shallow burial diagenesis. Additional diagenetic events including silica replacement, dissolution, and grain compaction were also observed in the study interval. These processes suggest early and late stage diagenesis respectively.