Drilling fluids play an important role in the drilling process: stabilizing the wellbore without damaging the formation, keeping formation fluids at bay, clearing cuttings from the bit face, and lubricating the bit and drill string, to name a few. The most critical function that a drilling fluid performs is to minimize the concentration of cuttings around the drill bit and throughout the well bore.
Drilling fluids went through major technological evolution, from using a simple mixture of water and clays, to complex mixtures of various specific organic and inorganic products used nowadays. With these components rheological properties can be improved and adapted. For example, if water is added to the mixture, the viscosity goes down over a wide shear rate range. If bentonite is added, the viscosity increases. Polymers help to increase the viscosity at high shear rates, white lime to increase the viscosity at lower shear rates.