Design and Evaluation of a Water-Based Drilling Fluid for Enhanced Wellbore Stability

Thesis Abstract

The stability of wellbore integrity during drilling operations remains a critical challenge in petroleum engineering, predominantly due to the complex interactions between drilling fluids and formation materials, which often result in wellbore collapses, fluid invasion, and non-productive time. This study seeks to address these issues by designing and evaluating a novel water-based drilling fluid optimized for enhanced wellbore stability. The primary aim is to formulate a sustainable, cost-effective, and environmentally friendly drilling fluid that mitigates formation damage and improves borehole stabilization, thereby reducing operational risks and costs. Specific objectives include understanding the physico-chemical properties influencing wellbore stability, developing a functional formulation incorporating stabilizing agents, evaluating its performance through laboratory investigations, and assessing its efficacy relative to conventional water-based fluids. The research employs an exploratory experimental research design, integrating both qualitative and quantitative methods, with the theoretical framework grounded in Darcy's law and the Geomechanical Theory of Wellbore Stability, complemented by the Theory of Particle Suspension. The population of the study comprises core samples from sandstone and shale formations representative of typical drilling environments, with lab-scale formulations tested on synthetic wellbore models. A sample size of 50 core samples and 10 different fluid formulations was used to ensure comprehensive performance evaluation. Data collection instruments include physicochemical analysis tools such as rheometers, filtrate measurement apparatus, pH meters, and erosion testing setups. The performance of the formulated fluids was assessed through laboratory experiments measuring parameters such as mud weight, rheological behavior, filtration rates, swelling potential, and shale stability, complemented by analytical techniques including regression analysis for performance prediction and ANOVA for comparative analysis of fluid formulations. The data analysis involves multivariate statistical methods to determine the relationship between fluid composition and wellbore stability parameters, with performance benchmarking against traditional water-based fluids. Additionally, finite element modeling techniques were used to simulate wellbore behavior under different fluid stability conditions, providing insight into the fluid's capacity to prevent collapse and formation disintegration. The expected findings suggest that the new formulation significantly improves wellbore stability indicators, such as reduced mud invasion, maintainable mud weights, and minimized formation swelling, validated by statistical significance at p<0.05. The study hypothesizes that incorporating specific polymeric additives and colloidal stabilizers enhances fluid-filtration properties and shale inhibition capacity. This research contributes to the existing body of knowledge by introducing an innovative, eco-friendly drilling fluid formulation backed by empirical evidence of superior wellbore stabilization performance. It demonstrates the applicability of interdisciplinary approaches combining geomechanics, chemical formulation, and statistical evaluation to optimize drilling fluid systems. The findings are expected to inform industry best practices, promoting sustainable drilling operations with minimized environmental impact and operational hazards. The main conclusion emphasizes that tailored water-based formulations, developed through rigorous laboratory and modeling techniques, can effectively address wellbore stability challenges. The study recommends further field pilot testing to evaluate scale-up potentials, including assessment under real drilling conditions, sediment transport capacity, and long-term formation interaction. Future research should explore the integration of nanomaterials to further enhance stability, as well as the economic analysis of the proposed formulation's deployment across diverse geological settings. The outcomes of this study serve as a foundation for advancing environmentally sustainable drilling fluids that align with industry standards and regulatory requirements, ultimately contributing to safer and more cost-efficient hydrocarbon extraction practices.