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The truck-mounted workover rig is one of the most widely used types of workover rigs. Its core feature is the integration of key components required for workover operations, such as the power system, transmission system, drawwork, and derrick, onto a heavy-duty truck chassis. Relying on the vehicle's own driving capability, it enables rapid relocation, balancing mobility and operational efficiency, and is widely applicable to conventional workover operations in onshore oilfields. The following is a detailed introduction from aspects including structural composition, core advantages, applicable scenarios, and key parameters: Ⅰ. Structural CompositionThe truck-mounted workover rig features an integrated design of "truck chassis and workover operation system", with all parts working in coordination. Heavy-Duty Truck ChassisAs the load-bearing and mobile platform of the entire equipment, it usually adopts a dedicated off-road truck chassis with multi-axle drive such as 6×4 or 8×4. Equipped with a high-horsepower engine (300-600 horsepower), a high-strength frame, and a robust suspension system, it can carry tens of tons of equipment weight and adapt to the driving needs of off-road oilfield sites. The chassis is also equipped with a high-power transmission (mostly manual or automatic) and reinforced tires (with off-road tread patterns and puncture resistance). Power SystemThe diesel engine built into the chassis serves as the main power source. Through a transfer case, power is distributed to the "driving system" and "workover operation system": when driving, it powers the wheels; during operation, the driving power is cut off to focus on providing energy for the drawwork, derrick lifting, etc.Some high-end models adopt a "dual-power system" (diesel-electric hybrid), which can switch to electric motor-driven operation to reduce noise and emissions at the well site. Core Workover Operation System Drawwork System: Installed in the middle of the chassis, it includes components such as a drum, braking devices (main brake and auxiliary brake), and wire ropes, and is responsible for hoisting and lowering pipe strings (such as sucker rods and oil pipes). Derrick System: A foldable or telescopic derrick (usually 18-30 meters in height). During operation, it is lifted by hydraulic cylinders to provide vertical working space. A crown block is installed on the top (forming a "traveling system" with the traveling block to amplify the drawwork's pulling force). Transmission and Control System: Including a gearbox, transfer case, clutch, etc., to realize power transmission and speed adjustment; equipped with a cab (separate or integrated), through control levers and instrument panels, it controls the start/stop of the drawwork, lifting/lowering of the derrick, braking, and other actions. Auxiliary Devices: Such as blowout preventers, hydraulic outriggers (extended to stabilize the vehicle body during operation), toolboxes, and mud circulation system interfaces, which improve operational safety and convenience. Ⅱ. Core AdvantagesStrong MobilityRelying on the driving capability of the truck chassis, it does not require additional trailer traction and can directly drive on oilfield roads (with a maximum speed usually 30-60 km/h). It can quickly relocate between multiple wellheads, especially suitable for oilfields with scattered wellheads (such as small and medium-sized onshore oilfields). High Operational EfficiencyAfter arriving at the well site, the vehicle body is stabilized by hydraulic outriggers and the derrick is lifted, and the operation preparation can usually be completed within 30 minutes (much faster than the assembly time of skid-mounted or fixed workover rigs), significantly reducing non-operational time. Compact StructureAll components are integrated on the chassis with a reasonable layout and small floor space, suitable for well sites with limited space (such as cluster well groups where multiple wellheads are densely distributed). Wide AdaptabilityEquipped with chassis and drawwork of different powers, it can cover workover needs from shallow wells (<1500 meters) to medium-deep wells (1500-3000 meters), and can complete conventional operations such as pump inspection, rod replacement, fishing, and well flushing. Ⅲ. Applicable Scenarios 1.Gobi and Desert Terrain Characteristics: The surface is mainly composed of sand and gravel, with relatively flat terrain but possibly shallow pits and washboard roads, and some areas are affected by wind and sand. Adaptation Reasons: The heavy-duty off-road tires (large size and deep tread) of the truck-mounted workover rig can reduce slipping on sandy and gravelly ground, and the puncture-resistant design reduces the risk of tire damage. Multi-axle drive chassis (such as 8×4, 6×6) with uniform power distribution can handle slightly undulating terrain. The enclosed cab and air filtration system can resist the impact of wind and sand on equipment and operators. 2. Hilly and Gentle Slope Terrain Characteristics: The terrain has a certain slope (usually ≤15°), with mostly dirt roads or unpaved roads on the surface, and possibly gullies and gravel piles. Adaptation Reasons: The chassis is equipped with a high-power engine (300-600 horsepower) and a low-speed, high-torque transmission, which can provide sufficient power for climbing. The vehicle body has a lower center of gravity (compared to skid-mounted ones), and with the anti-roll stability system, it is not easy to lose balance when operating on gentle slopes. The hydraulic outriggers can adjust the telescopic length according to the slope to ensure the vehicle body is level and stable during operation. 3.Grassland and Wetland Edges Characteristics: The surface is grassland or humus soil, which may be muddy in the rainy season but does not form deep swamps, with shallow water areas (water depth ≤30cm). Adaptation Reasons: Wide-base off-road tires (with large ground contact area) can reduce pressure on the ground and lower the risk of getting stuck. Some models are equipped with a central inflation and deflation system, which can adjust tire pressure according to the softness and hardness of the ground (deflating on soft ground to increase the contact area). The chassis guard plate can prevent grassland debris (such as stones and tree roots) from scratching the engine and transmission. Limitation: It can only operate at the edge of wetlands and cannot enter deep swamps (prone to getting stuck). 4.Mountainous Unpaved Road Areas Characteristics: Narrow roads, many curves, relatively steep slopes (≤20°), with gravel or soil on the surface, and possible falling rocks or gullies. Adaptation Reasons: The short-wheelbase chassis design (for some models) can improve turning flexibility, adapting to narrow mountain roads. The reinforced suspension system (leaf springs and hydraulic shock absorbers) can buffer bumps and protect equipment components. The four-wheel drive or all-wheel drive system with differential locks can distribute power when one side of the wheels slips, ensuring passage. Limitation: Falling rocks on the road need to be cleared in advance, and when the slope exceeds 20°, auxiliary trailer traction is required. 5.Saline-Alkali Soil and Mildly Saline-Alkali Land Characteristics: The surface contains high concentrations of salt, which hardens into lumps when dry and is prone to mud when rainy, causing corrosion to metal components. Adaptation Reasons: Key chassis components (such as the frame, wheel hubs, and braking system) are coated with anti-corrosion coatings or made of stainless steel to resist salt spray erosion. Tires are made of salt- and alkali-resistant rubber materials to avoid aging and cracking caused by salt. Regular cleaning of the chassis can reduce salt accumulation and maintain equipment performance. Limitations Limited Load-Bearing Capacity: Due to the load limitation of the truck chassis, the maximum hook load is usually ≤300 tons, which cannot meet the heavy pipe string operations in deep wells (>3000 meters) or ultra-deep wells (skid-mounted or crawler-mounted workover rigs are required). High Dependence on Chassis: The reliability of the chassis directly affects the attendance rate of the entire equipment, requiring regular maintenance (such as the engine, transmission, tires, etc.). Extreme Complex Terrains Not Suitable (Requiring Dependence on Other Equipment) Deep Swamps or Muddy Areas: The surface has extremely low bearing capacity, making it easy to get stuck and unable to get out by itself. Desert Hinterland (Mobile Sand Dunes): The soft sand will cause the wheels to sink completely, requiring crawler-mounted workover rigs or desert-specific vehicles for assistance. Steep Mountainous Areas (Slope >25°): The wheeled braking system is difficult to stably park, and there is a risk of overturning during operation. Flooded Areas or Deep Water Areas (Water Depth >50cm): It will cause engine water intake and short circuits in the electrical system. Ⅳ. Key Technical Parameters (Core Indicators for Selection) Maximum Hook Load: The maximum load that the drawwork can lift (unit: kilonewton kN or ton), which is a core indicator to measure operational capability. The common range is 100-300 tons (corresponding to well depths of 1000-3000 meters). Derrick Height: Determines the maximum length of the pipe string that can be hoisted and lowered, usually 18-30 meters (can be adjusted according to the length of a single oil pipe; for example, a 9-meter single oil pipe requires a derrick height ≥12 meters). Chassis Drive Form: Such as 6×4 (6 wheels, 4 driven), 8×4 (8 wheels, 4 driven), etc. The more driven wheels, the stronger the off-road capability (adapting to muddy and gravel roads). Engine Power: The chassis engine power is usually 200-500 horsepower. The higher the power, the more sufficient the load-bearing capacity and driving power. Braking System: The performance of the main brake (hydraulic disc or band type) and auxiliary brake (eddy current or water brake) directly affects operational safety (such as braking stability when lowering the pipe string). Ⅴ. Development TrendsWith the increasing requirements of oilfields for environmental protection and intelligence, modern truck-mounted workover rigs are developing towards "energy conservation and intelligence". Adoption of electric or diesel-electric dual-power systems to reduce fuel consumption and emissions. Equipped with remote monitoring and automatic control functions (such as automatic bit feeding and brake assist systems) to improve operational safety. Enhancement of the chassis's off-road performance (such as all-wheel drive and explosion-proof tires) to adapt to more complex well site road conditions. In conclusion, relying on the characteristics of "rapid relocation and efficient operation", the truck-mounted workover rig has become the main equipment for workover operations in onshore oilfields, and is an optimal solution balancing mobility and practicality.    

A workover rig is a specialized equipment in the oil and gas industry used for maintenance, repair, stimulation, and fishing operations of oil and gas wells. It is a key asset for ensuring the normal production of oil and gas wells and extending the lifespan of wellbores. It can perform various downhole operations on commissioned wells, such as replacing downhole strings, repairing wellbore structures, handling downhole faults, and implementing stimulation measures like acidizing and fracturing. Ⅰ. Main Functions and Principles Main Functions 1.Workover Operations Handling stuck pipes and fallen objects: Forcibly pulling out stuck strings through the hoisting system, or using the rotary table to drive fishing tools (such as fishing spears and overshots) to retrieve downhole fallen objects (e.g., broken rods, rocks). Replacing downhole equipment: Pulling out old tubing, sucker rods, and oil well pumps, and running in new equipment to restore the production capacity of the well. Casing repair: Patching, shaping, or reinforcing damaged casings to prevent wellbore collapse. 2.Stimulation Operations Assisting in acidizing and fracturing: Running fracturing strings up and down, connecting surface fracturing equipment, and injecting fracturing fluids into the formation to enhance production. Well cleaning and paraffin removal: Removing paraffin, scaling, or sediment from well walls through circulating hot water or chemical agents to improve oil flow channels. 3.Completion Operations Assisting in cementing, running production strings, and other completion processes after the drilling of new wells. 4.Fishing Operations Retrieving broken tools and strings in the well to restore wellbore integrity. Main Principles The core working logic of a workover rig is to drive mechanisms such as the drawworks and rotary table through the power system, utilizing the lifting capacity of the derrick and the rotational capacity of the rotary table to complete operations like tripping downhole strings and handling faults: 1.Tripping strings: The drawworks winds the wire rope, which, through the crown block sheave (usually 3-5 sheaves) composed of the crown block and traveling block, converts power into lifting force to suspend and hoist tubing, sucker rods, etc. When lowering, the speed is controlled by the braking system to ensure stable operation. 2.Rotational operations: The rotary table drives downhole drilling tools or casings to rotate through gear transmission, enabling operations such as casing milling and grinding (e.g., back-off and cutting when handling stuck pipes). 3.Auxiliary operations: Adjusting the derrick angle and extending outriggers through the hydraulic system to ensure the equipment is aligned with the wellhead; safety devices like blowout preventers (BOPs) control the risk of well kicks and blowouts during operations. Ⅱ. Basic Components A workover rig typically consists of the following core components: Substructure Mostly specialized heavy-duty truck substructures or crawler substructures, providing mobility and operational support.The substructure must have sufficient load-bearing capacity and stability; some models are equipped with hydraulic outriggers, which are deployed during operations to distribute weight and prevent tipping. Derrick Used to suspend and hoist downhole tools and strings, with a certain load-bearing capacity and height. 1.Main structure (derrick frame) Material: Mostly high-strength low-alloy steel (e.g., Q345, Q460), formed into a truss structure through welding or bolting, balancing light weight and high strength. Structure type: Mainly "quadrangular pyramid" or "portal" trusses, composed of columns, cross braces, and diagonal braces to form a stable spatial framework. Columns are the main load-bearing components, while cross braces and diagonal braces enhance overall rigidity to prevent deformation. 2.Crown block platform  Located at the top of the derrick, used to install the crown block and equipped with anti-collision devices, guardrails, and other safety facilities. The crown block consists of multiple sheaves, connected to the drawworks and traveling block via wire ropes to transmit force and change direction, serving as a key node in the hoisting system. 3.Derrick Substructure A supporting structure connecting the derrick to the workover rig substructure (or ground), used to raise the height of the derrick base and reserve space for wellhead operations (e.g., BOP installation, string connection). Some bases are telescopic or foldable to reduce height during transportation and expand to enhance stability during operations. 4.Guy line system For self-supporting derricks (non-tower type), multiple sets of guy lines (steel cables) are required to anchor the top of the derrick to the ground, balancing horizontal loads on the derrick to prevent tipping. One end of the guy line is connected to the lifting lug at the top of the derrick, and the other end is fixed to the ground anchor. The tension is adjusted via turnbuckles to ensure the derrick is vertically stable. 5.Erecting mechanism Used to raise and lower the derrick, usually driven by hydraulic cylinders, drawworks wire ropes, or chains. The lifting process requires strict control of speed and angle to avoid excessive stress-induced deformation of the derrick. 6.Safety accessories Crown block collision preventer: Automatically triggers drawworks braking when the traveling block rises close to the crown block, preventing "crown block collision" accidents. Ladders and guardrails: Safety channels for personnel to climb the derrick and operate on the monkey board, ensuring safety during high-altitude operations. Anti-slip pedals: Installed on the surfaces of platforms such as the monkey board and crown block platform to prevent personnel from slipping. Ⅲ. Classification According to mobility and operation scenarios, workover rigs can be classified into: Truck-mounted workover rigs: The most common type, mounted on heavy-duty truck substructures, with strong mobility, suitable for conventional onshore well operations. Crawler-mounted workover rigs: Adopting crawler substructures with low ground pressure, suitable for complex terrains such as muddy areas and mountainous regions. Skid-mounted workover rigs: Equipment disassembled into multiple skids, transported by trailers, and assembled on-site, suitable for fixed well sites or large-scale workover operations. Offshore workover rigs: Installed on drilling platforms or workover vessels, adapted to offshore oil and gas well operations, with corrosion resistance and wind-wave resistance. According to power and load capacity: Small workover rigs: Rated load < 300kN, used for simple maintenance of shallow wells (< 1000 meters), water wells, or low-yield oil wells. Medium workover rigs: Rated load 300-500kN, suitable for conventional workover operations of medium-deep wells (1000-3000 meters). Large workover rigs: Rated load > 500kN, used for deep wells (> 3000 meters) or complex wells (e.g., horizontal wells, high-pressure wells), capable of handling high-load and high-risk operations. Ⅳ. Industry Standards The design, manufacturing, and use of workover rigs must comply with relevant industry standards, such as China's SY/T (Oil and Gas Industry Standards) and the American Petroleum Institute (API) standards, to ensure their safety, reliability, and operational efficiency. In oil and gas field development, workover rigs complement drilling rigs: drilling rigs are responsible for "drilling wells," while workover rigs are responsible for "maintaining wells," jointly ensuring the efficient extraction of oil and gas resources.