resulting in the precipitation of insoluble salts Mud filtrate and formation fluids form an emulsion, reducing reservoir porosity Specially designed drill-in fluids or workover and completion fluids, minimize formation damage. Cool, lubricate, and support the bit and drilling assembly Source: Heat is generated from mechanical and hydraulic forces at the bit and when the drill string rotates and rubs against casing and wellbore. Cool and transfer heat away from source and lower to temperature than bottom hole. If not, the bit, drill string and mud motors would fail more rapidly. Lubrication based on the coefficient of friction.("Coefficient of friction" is how much friction on side of wellbore and collar size or drill pipe size to pull stuck pipe) Oil- and synthetic-based mud generally lubricate better than water-based mud (but the latter can be improved by the addition of lubricants). Amount of lubrication provided by drilling fluid depends on type & quantity of drill solids and weight materials + chemical composition of system. Poor lubrication causes high torque and drag, heat checking of the drill string, but these problems are also caused by key seating, poor hole cleaning and incorrect bottom hole assemblies design. Drilling fluids also support portion of drill-string or casing through buoyancy. Suspend in drilling fluid, buoyed by force equal to weight (or density) of mud, so reducing hook load at derrick. Weight that derrick can support limited by mechanical capacity, increase depth so weight of drill-string and casing increase. When running long, heavy string or casing, buoyancy possible to run casing strings whose weight exceed a rig's hook load capacity. Transmit hydraulic energy to tools and bit Source: Hydraulic energy provides power to mud motor for bit rotation and for MWD (measurement while drilling) and LWD (logging while drilling) tools. Hydraulic programs base on bit nozzles sizing for available mud pump horsepower to optimize jet impact at bottom well. Limited to: Pump horsepower Pressure loss inside drillstring Maximum allowable surface pressure Optimum flow rate Drill string pressure loses higher in fluids of higher densities, plastic viscosities and solids. Low solids, shear thinning drilling fluids such as polymer fluids, more efficient in transmit hydraulic energy. Depth can be extended by controlling mud properties. Transfer information from MWD & LWD to surface by pressure pulse. Ensure adequate formation evaluation Source: Chemical and physical mud properties as well as wellbore conditions after drilling affect formation evaluation. Mud loggers examine cuttings