**1. Introduction**

Oil well drilling operation is a common and important process in the petroleum industry. Drilling fluid is an essential operational fluid that plays an exceptional part in drilling engineering. In a rotary drilling operation, drilling fluids are circulated continuously in the wellbore and drilling string [1]. Drilling mud serves a variety of functions, including cleaning and transporting the borehole, maintaining the borehole integrity, reducing formation damage, and cooling and lubricating the tools. Water-based muds are popular due to their low cost and environmental protection requirements. It generally comprises water, clay, and other chemical additives for different purposes.

Various problems are encountered during drilling a wellbore, including clay swelling, shale instability, bit balling, drill string accretion, high torque and drag, differential sticking, and fluid losses. These issues put a substantial cost on the overall drilling operation. These issues further increase with the increase in the wellbore depth. In addition, the conventional muds containing clay, weighting agents, and pH controllers could not be applied in such conditions. This is due to the interaction of such

fluids with the clay minerals resulting in the variation in the mechanical properties by clay swelling. Hence, the design and selection of appropriate mud additives are the most critical factors that need to be considered. Oil-based muds (OBMs) are conventionally preferred due to their better thermal stability and nonreactive nature but due to the environmental concerns and their higher costs make them uneconomical. Thus, high-performance water-based containing eco-friendly additives are preferred. The concept of high-performance water-based drilling mud has been suggested for decades. It is a water-based drilling mud with acceptable rheology, minimal filtrate loss, high shale inhibition, good lubricity, and plugging properties [2].

The high-performance water-based mud (HPWBM) system was developed to enhance WBM performance while also providing an eco-friendly alternative to oilbased muds (OBM) while mimicking OBM drilling features. Various laboratory and field applications confirmed the HPWBM in replacing OBM by efficaciously accomplishing the objectives. HPWBMs have been recently developed as OBM alternatives, although not all kinds of HPWBM have been able to replace OBM on more complex wells. With the ever-increasing push for greater environmental performance and greater restrictions on the disposal of OBM cuttings, the petroleum industry is trying to design a WBM that can replicate OBM's performance [3].

High-performance muds are particularly advantageous to conventional waterbased systems because they provide faster penetration rates, enhanced hole cleaning, greater shale inhibition, and improved wellbore stability. The high-performance muds can deliver appropriate rheology and fluid stability under HTHP conditions, withstand high solids loading and deliver a high tolerance to brine or salt contamination, so the high-performance fluid is recommended for drilling the gypsum-salt formations and the reservoirs with natural fractures and inter-bedded shale. Such muds only tolerate operating temperatures up to 300°F because they depend on biopolymer-based viscosifiers. Deeper exploration in extreme high-temperature reservoirs (>300°F) requires new drilling fluid technologies.
