Geothermal energy development requires drilling into subsurface formations characterized by extreme temperatures, high pressures, chemically aggressive fluids, and complex geological structures. In these circumstances, drilling fluids, generally known as drilling muds, are essential for guaranteeing safe, efficient, and economical well building. This research offers an in-depth investigation of the performance of drilling fluids in geothermal wells, focusing on their thermal stability, rheological properties, chemical resistance, lubricity, and environmental compatibility. The report consolidates current research on water-based, oil-based, synthetic, and advanced nanoparticle-enhanced drilling fluids used in high-temperature geothermal settings. A methodological framework integrating laboratory evaluation, field data analysis, and comparative performance assessment is proposed. Research reveals that traditional drilling fluids frequently deteriorate under geothermal conditions, resulting in diminished viscosity, compromised fluid loss control, and wellbore instability, while advanced formulations utilising hightemperature polymers, inorganic additives, and nanoparticles exhibit enhanced performance. The research finds that optimising drilling fluid composition is crucial for enhancing drilling efficiency, minimising non-productive time, and maintaining well integrity in geothermal operations. Suggestions for further study and practical use are offered.