drillingfluid

Drilling fluid, or mud, is a circulating fluid used in the drilling of boreholes in petroleum exploration and production. It serves to cool and lubricate the drill bit, suspend and transport drilled cuttings to the surface, maintain hydrostatic pressure to prevent formation fluids from entering the well, and stabilize the wellbore by controlling formation pressures and wall collapse.

Common types include water-based mud (WBM), oil-based mud (OBM), and synthetic-based mud (SBM); gas-based systems are used in some underbalanced or specialized operations. The choice depends on geology, well design, and environmental and cost considerations.

Drilling fluids are composed of a base fluid, weighting agents (such as barite), clays (like bentonite), polymers and lubricants, salts, and various chemical additives that control rheology, filtration, and chemistry. Additives may include emulsifiers, shale inhibitors (e.g., potassium chloride), loss-circulation materials, and filtration control agents. Core functions include lubrication, cooling, hole cleaning, filtration control, and maintaining wellbore stability.

Key properties include flow rheology (plastic viscosity and yield point), density, filtration characteristics, and pH. They are tested with rheometers, density measurements, and filtration tests; surface equipment such as pumps and solids-control units separate solids and recover fluid for reuse.

Operations involve circulating the mud, conditioning it with surface equipment (mud pumps, shale shakers, desanders/desilters, centrifuges), and monitoring wellbore pressures. Environmental and waste considerations include handling, recycling, and disposal of spent mud and drill cuttings, with regulatory compliance and attention to toxicity and ecological impact.