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Ⅰ. Surface Equipment Unit Mud Tank Function: A core container for storing, settling, and preparing drilling fluid, typically consisting of 3-5 independent tanks (suction tank, cleaning tank, reserve tank, weighting tank) with a single tank capacity of 50-100 m³. Mud Pump Function: Mostly a triplex single action reciprocating pump with an outlet pressure of 30-100 MPa and a displacement of 100-3000 L/min;It extracts drilling fluid from the suction tank, pressurizes it, and delivers it to the surface manifold, providing power for downhole circulation. Surface Manifold Function: A pipeline hub connecting the mud pump, swivel, and solids control equipment, composed of a standpipe, hose, mud gate valve, pressure gauge, etc.; It can switch the flow direction of drilling fluid via gate valves, and the pressure gauge monitors circulation pressure in real-time to prevent overpressure accidents. Swivel Function: A rotating sealing device installed under the traveling block, with the upper end connected to the hose and the lower end connected to the drill string; It enables synchronous rotation and fluid delivery, allowing the drill string to rotate at high speed while maintaining leak-free transportation of drilling fluid. Solids Control Equipment Function: A purification and filtration system for drilling fluid, classified into four levels by purification precision: 1.Shale shaker (removes large cuttings, screen size 0.2-1.5 mm); 2.Desander (removes sand particles, separation size 40-74 μm); 3.Desilter (removes mud particles, separation size 15-40 μm); 4.Centrifuge (removes colloidal particles, separation size 2-15 μm); It removes over 95% of solid particles from drilling fluid to ensure stable properties such as viscosity and density. Ⅱ. The Circulation Process of Drilling Fluid The circulation process of drilling fluid consists of three core stages, forming a complete closed loop, with specific procedures as follows: Stage 1: Drilling Fluid Descent (Surface → Bottom Hole, Power Delivery) 1.The mud pump extracts prepared drilling fluid from the suction tank, pressurizes it, and delivers it to the standpipe of the surface manifold; 2.The drilling fluid flows through the standpipe into the hose and then into the swivel; 3.The swivel guides the drilling fluid into the drill string bore through its rotating sealing structure, which flows downward along the hollow channels of the drill pipe and drill collar, eventually reaching the bottom hole bit; 4.The drilling fluid is ejected at high speed through the bit nozzles, forming a high-pressure jet to impact the bottom hole formation, assist the bit in breaking rock, and flush cuttings at the bottom. Stage 2: Drilling Fluid Ascent (Bottom Hole → Surface, Function Implementation) 1.The high-speed ejected drilling fluid wraps the broken cuttings at the bottom hole, forming a cuttings-mud mixture; 2.Driven by the continuous pressure of the mud pump, the mixture flows upward along the annulus, while completing three key tasks: Cooling the bit: Absorbing heat generated by bit rotation (bottom hole temperature can reach 150-200°C) and carrying it back to the surface through circulation; Stabilizing the wellbore: Clay particles in the drilling fluid form a 2-5 mm thick "mud cake" on the wellbore wall, plugging formation pores and preventing wellbore collapse; Balancing well pressure: Balancing formation pressure through drilling fluid column pressure to prevent blowouts or lost circulation; 3.After the cuttings-laden drilling fluid reaches the surface, it first enters the shale shaker for preliminary filtration of large cuttings larger than 0.2 mm in diameter. Stage 3: Purification and Regeneration (Surface Treatment, Recyclable Reuse) 1.The drilling fluid preliminarily filtered by the shale shaker flows into the desander, where sand particles with a diameter of 40-74 μm are separated by centrifugal force; 2.The drilling fluid with sand particles removed enters the desilter for further separation of mud particles with a diameter of 15-40 μm; 3.For high-requirement deep wells/complex wells, the drilling fluid needs to enter the centrifuge to separate colloidal particles with a diameter of 2-15 μm; 4.The purified drilling fluid flows into the cleaning tank, where technicians adjust its properties using testing instruments; 5.The qualified drilling fluid enters the suction tank, awaiting the next cycle to achieve zero or low-emission reuse. Ⅲ. Four Core Functions of the Circulation System 1.Carrying and removing cuttings: Preventing pipe sticking accidents 2.Cooling and lubricating the bit: Extending equipment service life 3.Stabilizing the wellbore and controlling well pressure: Ensuring wellbore safety 4.Transmitting downhole information: Supporting intelligent drilling