**2. Drilling mud properties**

The success of any drilling fluid is dependent on the composition of the mud additives, which alters the mud properties. The two most common properties, including rheological and filtration, are primarily controlled while designing a drilling mud. Both properties can be improved with the utilization of mud additives. Various additives are added to the drilling to maintain the mud rheological and filtration characteristics. During drilling of the pay zone section, various polymers are added to replace bentonite to minimize the damage due to solids intrusion into the pay zone section. Such bentonite-free muds can form a thin and removable filter cake on the borehole wall and thus reduces the formation damage. Some of the most commonly used biopolymers are xanthan gum, guar gum, diutan gum, cellulose, lignins, and starches.

Generally, the viscosity is maintained lower for such muds, but more focus is paid to the filtration characteristics. It is worth mentioning that most water-based mud has shown best fitting with power-law and Herschel-Bulkley model. The laboratory experiments and field applications have observed that the flow behavior index (n) and consistency index (k) are the primary parameters controlling the cuttings transportation. The lower the flow behavior index and the higher the consistency index will perform better in cuttings transportation.
