Drilling fluids is a specialized field of study within subsurface engineering focused on the properties, behavior, and application of complex fluid systems used to facilitate the safe and efficient drilling of boreholes. This concept investigates their diverse functions, including cuttings transport, wellbore pressure management, formation stabilization, and lubrication, alongside their rheological, chemical, and thermal interactions with the downhole environment. Research in drilling fluids is paramount for optimizing drilling performance, minimizing operational risks, and addressing environmental considerations in oil and gas exploration, geothermal energy, and geotechnical projects.