Integrated Insights into Lithofacies, Fracture Networks, and Reservoir Productivity in Basement Reservoirs: A Comprehensive Case Study from the Cauvery Basin, India, Using Well Logs, Petrographic Studies, and Production Logs

Abstract

Summary The architecture and heterogeneity of basement rocks can play a crucial role in reservoir evaluation and hydrocarbon exploration. This study focuses on the comprehensive characterization of basement reservoir heterogeneities and fracture networks in the Cauvery Basin using a combination of petrophysical and geochemical analyses. The intricate interplay of lithological variations and chemical alteration processes in basement rocks significantly influences their complex nature. In this study, openhole log data acquired in the basement section from wells within the Cauvery Basin were analyzed. These log data were correlated with core studies to understand the lithofacies heterogeneities present within the basement reservoir. Furthermore, fracture data obtained from resistivity image log data were examined to understand the distribution and properties of fractures in relation to lithofacies heterogeneities. Notably, a higher fracture density was observed in the mafic-rich sections compared to the felsic-rich sections. The integration of resistivity image log data with lithofacies contributed to the understanding of the reservoir architecture. Additionally, elemental spectroscopy logging facilitated geochemical analysis, providing measurements of the elemental composition of basement, which were incorporated into the study. Production logging (PL) was performed in the study wells to ascertain the production from the basement reservoir. This analytical approach augmented the characterization of the basement reservoir and contributed to a holistic understanding of its properties. This study emphasizes the role of conducting a thorough analysis of petrophysical log responses in conjunction with detailed core studies to characterize basement reservoirs. The study successfully differentiated two distinct lithofacies units within the Cauvery Basin’s basement reservoirs: mafic-mineral-dominated and felsic-mineral-dominated and their impact on reservoir heterogeneities. Production log data validated hydrocarbon contributions primarily from felsic rocks, underscoring the importance of lithological variations.