**Abstract**

With the increase in energy demand, deeper wells drilling is one of the solutions to fulfill the energy demand, which demands specialized drilling mud formulation. These muds are composed of thermally stable materials that can sustain in hightemperature conditions. Biopolymers are widely used out of various mud additives for improving the rheology and filtration characteristics of mud. Owing to the high temperature and poor thermal stability of such additives, these additives lose their primary functions, resulting in the nonproductive time and irreversible problems. The book chapter highlights the uses of water-based mud, its limitations, and the degradation of biopolymers. Various additives' significance and susceptibility in harsh borehole conditions have been discussed. The existing additives used for the rheological and filtration characteristics improvements and their shortcomings are presented. Furthermore, the field applications of native and modified polymericbased mud formulations have been further examined and presented.

**Keywords:** drilling fluids, nondamaging muds, high-pressure, high temperature
