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The rotary system is a typical component of a rotary drilling rig, whose function is to drive the drill string to rotate for rock breaking. It consists of the rotary table, swivel, and drill tools. The composition of drill tools varies depending on the type of well being drilled; generally, they include the kelly, drill pipe, drill collar, and bit, along with accessories such as stabilizers, shock absorbers, and adapter subs. Among these, the bit is the tool that directly breaks rock. The drill collar, featuring high weight and thick wall, is used to apply weight on bit (WOB). The drill pipe connects surface equipment to downhole equipment and transmits torque. The kelly typically has a square cross-section; the rotary table drives the entire drill string and bit to rotate via the kelly. The swivel is a classic component of rotary drilling rigs, which not only bears the weight of the drill tools and enables rotational movement but also provides a channel for high-pressure mud. Ⅰ. Key Components Rotary Table Composed of horizontal bearings, bevel gears, square kelly bushing (SKB), and a housing, it mostly adopts a gear transmission structure. 1.Serves as the executive core of the rotary system, driving the kelly or drill string to rotate through gear transmission; 2.Provides wellhead support and bears part of the drill string weight; 3.The square kelly bushing (SKB) fixes the kelly to ensure stable torque transmission. Swivel Consists of a gooseneck, center pipe, rotating bearings, sealing devices, and a suspension assembly. Its top is connected to the hook, and the bottom is connected to the kelly. 1.When the hook and traveling block are stationary, the swivel drives the kelly to rotate while preventing drilling fluid leakage; 2.The gooseneck is connected to the drilling fluid pipeline, and the center pipe guides the drilling fluid into the drill string; 3.Bears part of the drill string weight through the suspension assembly and coordinates with the hoisting system to adjust WOB. Kelly A thick-walled steel pipe with a square or hexagonal cross-section, usually 9-12 meters in length, with drill pipe joints at both ends. 1.Its upper end is connected to the swivel, and the lower end is connected to the drill string via a drill pipe joint, transmitting torque from the rotary table or top drive to the downhole drill string; 2.Its square cross-section matches the square kelly bushing of the rotary table to prevent slipping during rotation. Top Drive Composed of an electric motor (or hydraulic motor), gearbox, main shaft, drill pipe make-up/break-out device, and drilling fluid channel, it is installed below the traveling block. 1.Can directly drive the drill string to rotate without frequent joint making-up (reducing tripping time); 2.Equipped with a built-in make-up/break-out device, it can automatically tighten and loosen drill pipe threads, improving operational efficiency; 3.Suitable for deep wells, ultra-deep wells, and extended-reach wells, reducing drill string fatigue damage. Ⅱ. Core Functions Torque Provision Converts the energy of power equipment into the rotational torque of the drill string, driving the bit to rotate at high speed (typically 30-150 r/min) and enabling the bit cones to break rock formations. Drilling Fluid Circulation Support The rotary table and swivel of the rotary system are equipped with central through-holes. Drilling fluid can be injected into the drill string through these holes and finally sprayed out from the bit nozzles, fulfilling three key roles: cuttings carrying, bit cooling, and drill tool lubrication. Drill String Centering Maintenance Through the positioning function of components such as the rotary table and kelly bushing, it ensures the drill string always moves along the central axis of the wellbore during rotation, preventing wellbore deviation caused by drill string offset (especially critical for vertical well drilling). Downhole Tool Compatibility Can be compatible with directional drilling tools (e.g., progressive cavity drillers (PCD), measurement while drilling (MWD) tools). By adjusting the rotation speed or coordinating with downhole power tools, it achieves precise control of the wellbore trajectory (e.g., deviation building and hold for horizontal wells). Ⅲ. Working Principle Torque Transmission Process Diesel engine/Electric motor → Gearbox → Bevel gears → Rotary table rotation → Square kelly bushing driving kelly rotation → Kelly transmitting torque to downhole drill string via drill pipe joint → Bit rotating to break rock. Drilling Fluid Circulation Process Drilling pump → High-pressure pipeline → Swivel gooseneck → Swivel center pipe → Kelly → Inside of drill string → Bit nozzles → Annular space of wellbore → Wellhead return → Mud tank (for cuttings separation and recycling). Ⅳ. Daily Maintenance Rotary Table: Regularly clean the gearbox, replenish gear oil, and inspect bearing wear; Swivel: Clean the center pipe after each tripping operation and check the lubrication status of rotating bearings; Top Drive: Regularly calibrate the torque sensor, and inspect the motor insulation performance and hydraulic system pressure.