Drilling fluid is a circulating fluid used in drilling process. It is a mixture of liquid, solid and chemical. For a long time in the past, drilling fluid was commonly called “mud” at home and abroad, which is not accurate. Solid particles in drilling fluid can be divided into harmful solid and useful solid.Drill cuttings are the most harmful solid phase in drilling fluid, which will affect the physical properties in the whole drilling process, and increase the density, viscosity, dynamic shear force, water loss, mud cake, abrasiveness, viscosity and flow resistance of drilling fluid. In the process of drilling, drill cuttings will also damage the oil and gas reservoir, reduce the ROP, increase the rotary table torque, cause the rig sticking, and also downhole complex situations, such as lost circulation and blowout. At the same time, the drilling cuttings will cause serious wear to the circulating system. In order to economically and effectively eliminate harmful solid phase from drilling fluid. It is necessary to deeply understand the composition characteristics of drilling fluid.

The main functions of drilling fluid is cleaning the well bottom and carrying drill cuttings; Cooling and lubricating the drill bit and drill string; Form mud cake to protect well wall; Control and balance pressure; Suspended drilling cuttings; Provide formation data; Protect oil and gas reservoirs from damage.

Sometimes the clean water can be used as drilling fluid in well drilling. But for deep well and complex drilling, water is not enough. There need to add other material such as barite, clay, salt, oil to increase the mud density to reach the using. In actual drilling project, drilling mud is more complex than we are thinking. In different drilling stage or different geologic situation, it will also need to mix kinds chemical material to keep the mud property. Drilling slurry is the most middle material with lots function, which directly influence the drill efficiency and safety. Choose the good drilling mud and solids control equipment to make sure the drilling work.