R&D of LW400×1200 Variable Frequency Controlled High-Speed Decanter Centrifuge

As oil and gas exploration and development progress, drilling depths are increasing, and downhole geological conditions are becoming increasingly complex and variable. In recent years, the widespread adoption and implementation of advanced drilling techniques—such as deep-well, ultra-deep-well, horizontal, and underbalanced drilling—have imposed more rigorous technical standards on drilling fluid solids control technology. Solids control technology is pivotal to ensuring the stable execution of various drilling processes and the smooth progress of operations.

As a core piece of solids control equipment, the centrifuge—when properly selected and matched to operating conditions—can precisely regulate drilling fluid density and remove harmful solid impurities. This not only enhances mechanical drilling efficiency and extends the service life of auxiliary equipment (such as drilling pumps, drill strings, and downhole tools) but also reduces costs associated with drilling mud and chemical additives, while effectively protecting oil and gas reservoirs; thus, it holds immense value for engineering applications.

Currently, the vast majority of domestic drilling crews utilize medium-speed centrifuges characterized by power ratings of 18.5–220 kW, bowl diameters of 350–450 mm, and operating speeds of 1500–1850 rpm. However, with the iterative upgrading of drilling technologies, this traditional equipment can no longer meet the demands for high-precision solids control. The operational limitations of medium-speed centrifuges have become particularly apparent during the construction of specialized wells that require strict control over drilling fluid solids parameters. Their primary shortcomings lie in insufficient on-site processing capacity and poor adaptability to high-density, high-viscosity drilling fluids. Limited by operating speeds of 1500–1850 rpm and low separation factors, the equipment offers limited separation precision; it can only remove solid particles 10 μm or larger, failing to effectively eliminate fine, harmful solids, which results in poor overall adaptability for field applications.

Furthermore, the operating parameters of traditional drilling fluid centrifuges lack adjustability, making them highly susceptible to various malfunctions during operation. When parameters such as drilling fluid density, viscosity, and solids content fluctuate, the generation of solid impurities surges, easily triggering malfunctions like centrifuge rotor stalling or clogging. Once the equipment clogs, significant manpower and material resources are required for clearing and maintenance; furthermore, severely damaged units may need to be returned to the factory for repairs, substantially increasing operational costs. More critically, failure of the equipment's overload protection system can lead to major issues—such as control system malfunctions or motor burnout—resulting in unnecessary economic losses. Compared to other solids control equipment like shale shakers, traditional centrifuges offer lower operational stability and cannot sustain long-term continuous operation; they are limited to intermittent regulation of drilling fluid density and viscosity and cannot coordinate with shale shakers to perform continuous, fine solids removal across the entire well section, making them ill-suited for the demands of modern drilling operations.

my country began introducing medium-speed centrifuges for drilling operations in the mid-1990s, gradually validating their vital role in drilling fluid solids purification and the construction of wells requiring specialized techniques. However, as drilling operations become more challenging and solids control standards continue to rise, a system relying solely on medium-speed centrifuges can no longer address the complexities of precision solids treatment in drilling fluids. To meet the development needs of new drilling technologies and comprehensively elevate the domestic standard of drilling fluid solids control, there is an urgent need to optimize centrifuge performance and develop high-speed centrifuges characterized by high processing capacity and stability, specifically tailored to the geological and operational conditions of my country's oilfields.

The LW400×1200 high-speed variable-frequency centrifuge developed here features a core structure comprising a bowl assembly (including the bowl and screw conveyor), a main drive motor, the equipment housing, a base, a fully variable-frequency automatic control system, a feed pump, and various auxiliary facilities. The equipment operates as follows: the main motor drives a planetary differential via a belt transmission; the planetary differential then drives the bowl and the screw conveyor to rotate synchronously. Both components rotate in the same direction with a fixed speed differential, with the screw conveyor typically rotating at a slightly lower speed than the bowl. As the bowl rotates at high speed, high-density solid particles within the drilling fluid are forced against the inner wall of the bowl by centrifugal force; a screw conveyor scraper then dislodges these particles and pushes them toward the underflow discharge port. Meanwhile, the separated liquid phase flows out through the overflow port, thereby achieving efficient solid-liquid separation of the drilling fluid.

Both the centrifuge's main motor and the slurry pump motor are equipped with variable frequency control, real-time load monitoring, and feedback control modules, forming an integrated, fully variable-frequency automatic control system. With the exception of the sensor assembly connected to the equipment's differential gear unit, all electronic control components are housed within a single control cabinet, creating an integrated control unit. This unit not only offers intelligent, end-to-end control capabilities but also complies with explosion-proof safety standards for the petroleum drilling industry; furthermore, it features a built-in vibration-dampening structure suitable for the demanding conditions of field operations. To ensure the stable operation of the variable frequency system, the control cabinet supplements the variable frequency drive's (VFD) own heat dissipation design with a system that links real-time temperature monitoring to fan control. The system monitors the internal temperature of the cabinet in real time; if the temperature exceeds the VFD's rated operating threshold, a cooling fan automatically activates to cool both the cabinet and the VFD. Once the temperature returns to a safe range, the fan automatically shuts down, enabling intelligent start-stop control of the cooling system. The structural design of the LW400×1200 high-speed centrifuge, featuring full variable-frequency drive and automatic control, offers several significant advantages:

a) It employs a high length-to-diameter ratio (L/D) of 3:1, which substantially improves solid-phase dewatering, reduces liquid-phase loss in the drilling fluid, and saves on operational consumables;

b) Optimized differential speed parameters effectively enhance solids discharge capacity and sediment transport rates, leading to significantly higher operational efficiency;

c) The entire unit utilizes a rolling-element bearing support structure, effectively reducing operational vibration and enabling prolonged continuous operation, thereby greatly improving stability and reliability;

d) The screw flights are manufactured from highly wear- and corrosion-resistant materials, effectively withstanding the corrosive nature of drilling fluids and the abrasive action of solid particles, thus extending service life;

e) It features an integral dual-flight screw conveyor structure; this design simplifies manufacturing and processing while significantly boosting sediment transport efficiency;

f) An adjustable liquid level mechanism allows for flexible control of the solids drying zone length and precise regulation of sediment moisture content, meeting the requirements of diverse operating conditions.

1. Variable-frequency speed regulation and automatic control performance

The equipment's intelligent control system acquires conveyor torque signals from the fixed shaft end of the centrifuge's differential gear unit. These real-time signals are transmitted to the variable-frequency control system for comparison and analysis against preset parameters. Based on dynamic torque fluctuations, the variable-frequency drive and main control system provide real-time feedback to adjust the feed pump speed and the main bowl motor speed, dynamically managing feed volume and operational load to create a closed-loop intelligent control system. When parameters such as drilling fluid density, viscosity, or solids content fluctuate, the equipment maintains optimal operating conditions and ensures constant solids discharge. This effectively prevents issues like clogging or overload-induced shutdowns, significantly enhancing on-site adaptability and operational reliability.

The control system incorporates three torque threshold parameters: maximum torque for safety shutdown (Mmax), maximum operating torque (M1), and minimum torque for no-load startup (Mmin). During operation, the torque sensor at the fixed end of the differential continuously monitors dynamic torque (M). When the detected value falls within the range of Mmin < M < M1, the equipment operates in a stable, standard state; the main motor and the slurry pump motor run at the maximum speeds set by the variable frequency drives, ensuring the smooth execution of drilling fluid processing and solids discharge.

When the detected torque falls within the range of M1 < M < Mmax, it indicates an increase in operating load and solids processing pressure. In response, the control system utilizes real-time torque signals to automatically reduce the slurry pump speed and fluid feed rate, thereby lowering the main unit's load. This proactively prevents equipment clogging and overload failures until the torque returns to the normal operating range, ensuring continuous, stable operation.

2. Field Application Test

On December 17, 2004, the LW400×1200 high-speed variable-frequency centrifuge completed its field application test with Drilling Team 32559 of the Shengli Huanghe Drilling Company No. 4 at the Chun 68-Xie 5 well site. This well was a directional slant well with dual targets and a designed depth of 2,941 meters; the complex downhole drilling conditions demanded extremely high standards for drilling fluid stability and solids control precision. Following the commencement of the second drilling phase, the LW400×1200 centrifuge was put into operation. Throughout the application period, the drilling fluid density remained stable between 1.03×10³ and 1.26×10³ kg/m³, and the equipment achieved an actual processing capacity of 35–45 m³/h. The main unit operated stably at 2,800–3,000 r/min, demonstrating smooth overall performance, excellent solids discharge, and normal operating conditions for all components.

The equipment's fully variable-frequency automatic control system accurately captured torque feedback signals and adaptively adjusted processing throughput and operating load based on dynamic changes in drilling fluid properties, successfully achieving the design goal of constant-rate solids discharge. The temperature rise of the main bearings was only approximately 28°C, and the operating noise level was 85 dB; all operational indicators remained within normal ranges. On January 9, 2005, the well was successfully drilled to a final depth of 2,941 meters. By August 2005, the equipment had been successfully deployed in industrial applications across six wells drilled by the 32559 Drilling Team (including wells Chun 68-Xie 5, 3-9-206, 2-3-Xie 221, and 1-2-423). In all cases, the unit was utilized following the commencement of the second drilling phase; it demonstrated excellent purification performance for both weighted and unweighted drilling fluids, yielding significant operational results.

3. Conclusion

The LW400×1200 high-speed variable-frequency centrifuge features a compact structure, stable operation, and a long service life. It effectively removes fine, harmful solid particles larger than 3 μm from drilling fluids, precisely recovers the liquid phase, and stabilizes fluid performance parameters. Capable of significantly increasing the rate of mechanical penetration (ROP), it serves as an ideal purification unit for specialized wells, such as deep wells and horizontal wells. When used in conjunction with a double-deck high-frequency linear shale shaker for weighted water-based drilling fluid operations, the centrifuge enables precise control of fluid density and viscosity as well as stabilization of solid content. This combination effectively resolves industry-wide challenges regarding difficult solids control and the poor adaptability of traditional equipment in weighted mud sections.

The successful development of the LW400×1200 fully variable-frequency, automatically controlled high-speed centrifuge overcame key technical hurdles—specifically real-time load monitoring and fully variable-frequency closed-loop control—resulting in a complete process technology with independent intellectual property rights. The technology has been granted two national patents (Patent Nos.: 200520081438.3 and 200520081441.5). This equipment comprehensively upgrades the performance of domestically produced high-speed centrifuges and is suitable for solids control throughout the entire drilling process. It offers ease of operation and maintenance, reduces labor intensity for personnel, and effectively eliminates issues such as equipment clogging and fluid loss often encountered when handling high-solids, high-density drilling fluids. Thanks to its exceptionally high operating speed, this equipment removes fine solid impurities that conventional solids control systems cannot handle, thereby significantly reducing the content of harmful solids in the drilling fluid. In terms of operational benefits, it boosts drilling speed, lowers costs, optimizes drilling fluid rheology, extends the service life of auxiliary drilling equipment, reduces drill string wear, and ensures the stable operation of precision downhole instruments such as Measurement While Drilling (MWD) tools. Regarding resource conservation and safety, it effectively protects oil and gas reservoirs and maintains wellbore stability, offering immense economic value and significant potential for widespread adoption.