Abstract

Sandstone reservoirs often consist of clay minerals, including kaolinite, illite, and chlorite. These clay minerals have a pronounced effect on the reservoir quality, which makes their characterization and quantification crucial for the optimum extraction of hydrocarbon resources. In response to these challenges, this study aims to comprehensively evaluate the clay mineral composition, and depositional environment in reservoir rock using spectral gamma-ray (SGR) logs and laboratory samples. The results from the Th (ppm) versus K (%) analysis reveal that illite predominates as the clay mineral, exhibiting a higher potassium content compared to mixed-layer clays or smectite. Furthermore, this examination highlights the significant influence of primary and secondary factors, such as diagenesis and weathering, on the potassium and thorium content within clay minerals, thus impacting their characterization. Additionally, the Th/U ratios indicate a sand-rich marine to shallow marine depositional environment. Moreover, the findings derived from analyzing the Th/K (ppm/%) versus Pef (B/E) and Th/K (ppm/%) versus Th/U (ppm) relationships align consistently with earlier results. These findings further support the presence of illite and mixed clay layers, with micas and minor glauconite concentrations within the reservoir, suggesting a marine to shallow marine depositional environment. However, it's essential to acknowledge the limited reliability of the Th/U ratio plot in identifying depositional settings, particularly in organic-rich rocks. These results show the importance of integrating spectral gamma-ray log analysis with laboratory sample examinations to achieve accurate characterization of clay mineralogy and depositional environments. This comprehensive analysis also facilitates the investigation of the correlation between organic matter and uranium concentrations. Additionally, these findings would aid in a better understanding and characterization of reservoir facies in the Lower Goru Formation.