Devonian-Mississippian Chattanooga shale plays in North America are categorized as unconventional reserves with potential hydrocarbon resource accumulations. Unlike Chattanooga shale in the Appalachian region, less effort has been dedicated to its correspondent in the Ozark region. The ultra-tight nature of the formation causes fast decline of the production and small recovery factors. Application of EOR techniques such as CO2 flooding, among other techniques, can potentially improve the recovery of Chattanooga reservoirs. Characterization of these reservoirs is therefore an essential step to fully understand the associated complexities of the reservoir as well as to evaluate the economic viability of their exploitation. This paper therefore presents a fully integrated characterization at multiple scales including petrophysical, geophysical and geological evaluation, geomechanical and geochemical analysis of the black shale sequence in Sumner County, Kansas. Multi-scale dataset for this regional characterization is obtained from laboratory measured petrophysical parameters, well-log measurements as well as post-stack depth (PoSDM) seismic data.

Chattanooga shale in Sumner County has an average TOC of ~2.26 wt. % in the middle shale member with additional organic porosity of 5% and a vitrinite reflectance (Ro %) of 0.62. It is classified as a shale oil resource with OOIP of 4 MMbbl. Petrophysical correlations developed at wellbore vicinity were trained with artificial neural networks (ANNs) and correlated with seismic to provide lateral distribution of such properties farther from the wellbore. Moreover, due to the heavy reliance of unconventional shale plays on fracture network for improved flow conditions, fracture models were developed based on the mineral-brittleness as well as the fracture toughness. Consequently, a complete study based on compositional numerical simulation was conducted to analyze the potential of CO2 as an EOR technique, together with an evaluation of the impact of reservoir and fracture parameters in the well productivity potential. Subsequently, an economic optimization process was also formulated to obtain the best gas injection design for the highest Net Present Value (NPV). The cumulative oil was notably observed to increase by the use of the optimum injection design. Moreover, the huff-n-puff injection of CO2 proved to be a viable option by increasing the final oil recovery from 10% to 53% using optimal parameters.

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