The Benefits of Spectral Gamma Ray Log For Clay Minerals Identification in Brunei's Wells and Outcrops / 'Amila Fashihah binti Haji Abu Bakar

Thesis submitted for the degree of Master of Science Universiti Teknologi Brunei

Shale and clay-rich formations pose significant challenges in the oil and gas industry, primarily due to wellbore instability issues such as shale sloughing and clay swelling. These problems arise when reactive clay minerals, particularly montmorillonite, interact with drilling fluids, resulting in hydration and subsequent volumetric expansion. In Brunei, most wells contain slurry montmorillonite, which presents a substantial risk of formation swelling and collapse when exposed to water-based drilling fluids. Consequently, the appropriate selection of drilling equipment, tools, and fluid systems is critical for maintaining wellbore stability and optimizing drilling performance. The integration of geomechanical analysis and advanced drilling fluid design plays a crucial role in mitigating these challenges, reducing non-productive time, and enhancing hydrocarbon recovery. This study aims to predict potential problematic zones by analyzing the distribution and proportion of mixed-layered clay minerals relative to residual clay compositions. A comprehensive geostatistical approach is employed to examine the spatial variability of radioactive elements such as thorium, potassium, and uranium within the formations. Variogram modeling and kriging interpolation techniques are utilized to establish correlations between these elements and clay mineral composition, offering insights into the geological and petrophysical characteristics of the subsurface. Additionally, the study applies cross-plotting techniques between thorium and potassium values, obtained through the Spectral Gamma Ray Logging (SGRL), to enhance clay mineral characterization. By integrating geostatistical analysis with spectral gamma-ray logging data, this research seeks to improve the identification and classification of clay minerals in Brunei’s subsurface formations. The findings are expected to contribute to more effective assessments of formation stability, aiding the development of optimized drilling strategies and reservoir management practices. Ultimately, this study enhances the understanding of clay mineral distributions, supporting improved wellbore design, increased drilling efficiency, and reduced formation-related challenges in hydrocarbon exploration and production.

Thesis (Master) - Universiti Teknologi Brunei, 2025

Includes bibliographical references from page 69-77