Nur Iman Syuhada Binti Norazman creator author. text my 2025 2025 monographic eng viii, 70 pages : illustrations ; Shale instability is a significant challenge in drilling operations, particularly when using water-based mud (WBM). The interaction between reactive shale formations and WBM components can lead to hydration and swelling of clay minerals, resulting in wellbore instability, stuck pipe incidents, and increased drilling costs. To address these issues, this study focuses on developing and evaluating novel shale swelling inhibitors to improve drilling performance in shale formations. The primary objectives of this research are to prepare a WBM formulation and analyze its properties, formulate shale swelling inhibitors using a mixture of polyethyleneimine (PEI) and potassium citrate (PC), and compare the performance of these proposed inhibitors with a commercial shale swelling inhibitor. To achieve these objectives, a systematic methodology was employed, including shale inhibitor preparation, mud formulation, rheological and compatibility assessments, and various performance tests. The rheological evaluation involved measuring density, pH, plastic viscosity, apparent viscosity, yield point and gel strength at 10 seconds and 10 minute s. Performance testing included filtration properties and mud cake thickness under Low- Pressure Low-Temperature (LPLT) and High-Pressure High-Temperature (HPHT) mud filter press tests, linear swelling tests to quantify dimensional changes in shale samples, and the Cation Exchange Capacity (CEC) methylene blue index test to assess shale reactivity. Additionally, Scanning Electron Microscopy (SEM) was utilized to examine microstructural changes in shale samples, providing insights into inhibition mechanisms. The findings revealed that the inhibitor formulation comprising 0.4 v/v% PEI + 0.6 v/v% PC demonstrated the highest effectiveness and compatibility with WBM. This formulation significantly reduced shale swelling while maintaining desirable drilling fluid properties, making it a promising candidate for mitigating shale instability. In conclusion, the results of this study indicate that the newly developed shale swelling inhibitor effectively minimizes hydration and swelling, enhancing wellbore stability and improving overall drilling efficiency. Its superior performance suggests that it can serve as a viable alternative to commercial inhibitors, optimizing drilling fluid properties while reducing operational risks and costs. specialized Nur Iman Syuhada Binti Norazman Faculty of Chemical and Process Engineering Technology Final Year Report (Bachelor of Technology Mechanical Engineering (Petroleum) with Hons ) -- Universiti Malaysia Pahang Al-Sultan Abdullah - 2025 Include bibliographical reference Faculty of Chemical and Process Engineering Technology Dissertations Universities and colleges Dissertations Theses Dissertations THE0010915 (Local) https://umpir.ump.edu.my/id/eprint/48085 https://umpir.ump.edu.my/id/eprint/48085 UMPSA 260806 20260806124142.0 eng