Development of LW400 × 1200 Variable Frequency Control High Speed Centrifuge

With the development of petroleum exploration and development work, drilling depth continues to increase, and drilling encounters increasingly complex formations. Especially in recent years, the development and application of some new drilling technologies at home and abroad, such as deep and ultra deep well drilling technology, horizontal well drilling technology, and unbalanced drilling technology, have put forward higher requirements for solid phase control of drilling fluid. Drilling fluid and solid phase control technology are the key to ensuring the implementation of normal drilling technology. Centrifuges, as a type of drilling fluid solid control equipment, can be designed and used reasonably to effectively control the density of drilling fluid, remove harmful solid phases in drilling fluid, improve mechanical drilling speed, prolong the service life of subsequent equipment (drilling pumps, drilling tools, downhole instruments, etc.), save mud and drug usage, and protect oil and gas reservoirs, which is of great significance. At present, almost all drilling teams in China are equipped with a power of 18.5-220 kW and a drum diameter of? The medium speed centrifuge with a speed of 350-450mm and a speed of 1500-1850r/min is no longer able to meet the higher requirements of the new drilling technology. Especially for some special process wells with high requirements for solid phase control of drilling fluid, it is difficult to bear the heavy responsibility of using a medium speed centrifuge on site. The main reason is that the actual processing capacity on site is small, especially for drilling fluids with high density and viscosity. The drum speed is low, usually only 1500-1850r/min, and the separation factor is small. Due to the low rotational speed and large separation midpoint of the centrifuge, there are few harmful solid particles removed from the drilling fluid. Generally, only a portion of solid particles with an equivalent diameter of 10 μ m or more can be removed, resulting in poor on-site adaptability. At present, due to the non adjustable performance parameters of drilling fluid centrifuges, some problems often occur. For example, when the performance parameters of drilling fluid change (density, viscosity, solid content, etc.), due to the large amount of solid generated, the centrifuges often experience blockage. Once the centrifuge is blocked, a large amount of manpower and material resources must be spent on unblocking, and sometimes it must be returned to the manufacturer for maintenance and unblocking; More seriously, if the overload protection device of the centrifuge malfunctions, it can cause control system and motor failures, resulting in unnecessary economic losses. Compared to other solid control equipment, centrifuges have lower reliability and cannot operate continuously like vibrating screens. They are only occasionally used to control the density and viscosity of drilling fluid, and are not used in conjunction with vibrating screens in the entire well process to continuously remove small solid particles from drilling fluid.

China only began to use medium speed centrifuges in the mid-1990s and recognized their significant role in solid phase control of drilling fluids, especially in drilling special process wells. However, as the difficulty of drilling technology increases and the requirements for solid control continue to increase, only medium speed centrifuges cannot effectively solve the problem of solid control in drilling fluids today. To meet the needs of the development of new drilling technology and improve the solid control level of drilling fluid, it is necessary to improve the performance of the centrifuge. Especially, it is necessary to develop high-speed centrifuges with large displacement, high reliability, and suitable for the actual characteristics of China's oil mines.

The LW400 × 1200 high-speed centrifuge structure is composed of a drum assembly (including the drum and screw conveyor), a main motor, a casing, a base, a fully variable frequency automatic control system, a liquid supply pump, a large and small base, and auxiliary facilities. The main motor drives the planetary differential to rotate through a belt, and the planetary differential drives the drum and spiral conveyor to rotate respectively, making the two turn the same, but there is a speed difference. Generally, the speed of the spiral conveyor is slightly lower than that of the drum. Due to the high-speed rotation of the drum, dense solid particles adhere to the inner wall of the drum under the action of centrifugal force. They are scraped down by the scraper of the screw conveyor and pushed to the bottom flow hole for discharge. The separated liquid phase is discharged through the overflow hole, achieving the purpose of solid-liquid separation.

The main motor of the centrifuge and the motor of the slurry pump are respectively equipped with a variable frequency centrifuge load real-time acquisition and feedback control part and other electrical control components to form a fully variable frequency automatic control system. Except for the sensor connected to the differential of the centrifuge, all other components are installed in a control box to form an integrated control device. This device not only has control functions, but also meets the explosion-proof requirements of the petroleum drilling industry and has shock absorption function. In addition to the heat dissipation function of the frequency converter itself, in order to ensure the normal operation of the frequency converter, a real-time temperature detection and fan linkage control device is installed in the control box. When the temperature inside the control box is detected in real-time to be higher than the set temperature (which ensures the normal working temperature of the frequency converter), the fan cooling control box and frequency converter can be automatically started; When the real-time detection of the temperature inside the control box is lower than the set temperature (which is to ensure the normal working temperature of the frequency converter), the fan can be automatically turned off.

The structure of the LW400 × 1200 fully variable frequency automatic control high-speed centrifuge mainly has the following characteristics:

a) A large aspect ratio (aspect ratio of 3) makes the solid phase more dry and reduces the loss of drilling fluid.

b) The differential speed ratio is large, which improves the centrifugal machine's slag removal capacity and sediment transportation speed.

c) All are supported by rolling bearings, reducing vibration, facilitating long-term operation, and improving work reliability.

d) Spiral blades have high wear resistance and corrosion resistance, which improves the service life of spiral blades.

e) Adopting a conveyor structure with integral double spiral blades, it is easy to process and improves the efficiency of sediment transportation.

f) The liquid level adjustment device facilitates the adjustment of the length of the drying zone and the dryness and wetness of the sediment.

2. Automatic control performance of variable frequency speed regulation

Pick up the torque signal of the conveyor from the fixed shaft end of the centrifuge differential, and then input this torque signal into the frequency converter control system and compare it with the set value. The frequency converter and control system directly feedback the speed of the slurry pump and the main motor speed of the driving drum based on the changes and comparison results of the torque signal, thereby changing the slurry supply and the load of the centrifuge, and forming a closed cycle. This ensures that the centrifuge is always in optimal working condition when parameters such as drilling fluid density, viscosity, and solid content change, achieving the function of constant slag discharge without causing blockage and overload, thereby greatly improving the reliability and on-site adaptability of the centrifuge.

Set three torque signal values in the control system: maximum safe shutdown torque Mmax, maximum working torque M1, and minimum normal no-load starting torque Mmin. When the dynamic torque M detected in real-time by the torque sensor at the fixed end of the differential is less than the maximum working torque M1 setting value and greater than the normal no-load starting minimum torque Mmin setting value (i.e., Mmin<M<M1), the centrifuge remains in normal working condition. At this time, the main motor and slurry pump motor operate at the highest speed set by the frequency converter to ensure that the centrifuge can process drilling fluid and discharge slag normally.

When the dynamic torque M detected in real-time by the torque sensor at the fixed end of the differential is greater than the maximum working torque M1 setting value and less than the maximum stopping torque Mmax setting value (i.e., M1<M<Mmax), it indicates that the centrifugal load has increased. At this time, the real-time collected torque signal can directly reduce the speed and liquid supply of the slurry pump through the frequency converter and its control system, thereby reducing the load on the centrifuge host and avoiding centrifuge blockage and overload phenomena. Until the real-time detected dynamic torque M is less than the maximum working torque M1 set value, in order to ensure that the centrifuge does not experience overload.

3 Main technical parameters

4. On site application

On December 17, 2004, it was applied on-site at the 32559 drilling team of Shengli Yellow River Drilling Company No. 4. The first well is Chun-68-Xie5 well, which is a dual target directional deviated well with a designed depth of 2941m. The drilling process of this well is complex and requires high solid control of the drilling fluid, requiring stable drilling fluid performance. After the second drilling of the well, the LW400 × 1200 high-speed centrifuge was used, and the drilling fluid density remained stable at 1.03 × 103-1.26 × 103kg/m3. The actual processing capacity reached 35-45m3/h, and the main engine speed was 2800-3000r/min for stable operation. The slag removal effect was good, and all parts operated normally. Especially, the fully variable frequency automatic control system can fully collect torque feedback control signals based on changes in drilling fluid performance, automatically adjust the centrifuge processing capacity and centrifuge load, and achieve the design performance of constant slag discharge. The temperature rise of the main bearing is normal, only about 28 ℃, and the overall noise of the machine is 85dB, indicating normal operation. On January 9, 2005, the well was successfully completed with a depth of 2941m. As of August 2005, the centrifuge has been used in industrial applications in six wells, including Pure 68-Xiang5, 3-9-206, 2-3-Xiang221, and 1-2-423, in the 32559 drilling team. Each well has been in use since the second drilling operation, and both weighted and non weighted drilling fluids have been effective, achieving very good results.

5 Conclusion

The LW400 × 1200 high-speed centrifuge has the characteristics of compact structure, long service life, and reliable performance. It can remove harmful solid particles above 3 μ m, recover liquid phase, and effectively control drilling fluid performance, improve drilling speed. It is an ideal drilling fluid purification equipment for special process wells such as deep and horizontal wells. In weighted water-based drilling fluids, medium and high-speed centrifuges can be used in combination with double-layer high-frequency linear vibrating screens to maintain drilling fluid density, control solid phase and drilling fluid viscosity, thereby solving the problem of using centrifuges in weighted mud sections.

The LW400 × 1200 fully variable frequency automatic control high-speed centrifuge has been successfully developed, forming a drilling fluid high-speed centrifuge load real-time monitoring and fully variable frequency automatic closed-loop control technology with independent intellectual property rights in China. It has obtained two patent authorizations, with patent numbers 200520081438.3 and 200520081441.5, respectively. This greatly improves the performance of the high-speed centrifuge and can be applied to solid phase control in the entire drilling process. It is easy to operate, easy to use and maintain, reduces labor intensity of workers, and will not cause blockage or running of drilling fluid due to high solid content and density of drilling fluid.

Due to its high rotational speed, it can remove fine solid particles in the drilling fluid that cannot be removed by other solid control equipment, significantly reducing the content of harmful solid particles in the drilling fluid. There are significant economic and social benefits in improving drilling speed, reducing drilling costs, improving the rheological properties of drilling fluids, prolonging the service life of subsequent equipment, reducing drilling tool wear, using advanced downhole instruments (such as MWD), protecting oil and gas reservoirs, and maintaining wellbore stability.