OPTIMIZATION AND APPLICATION OF RECIPROCATING DIRECT-DRIVE ELECTRIC SUBMERSIBLE PLUNGER PUMP LIFTING SYSTEM IN THE XINJIANG OILFIELD

Educational Research in Universal Sciences ISSN: 2181-3515 VOLUME 4 | SPECIAL ISSUE 13 | 2025 https://t.me/Erus_uz Multidisciplinary Scientific Journal October, 2025 13 DOI: https://10.5281/zenodo.17489024 OPTIMIZATION AND APPLICATION OF RECIPROCATING DIRECTDRIVE ELECTRIC SUBMERSIBLE PLUNGER PUMP LIFTING SYSTEM IN THE XINJIANG OILFIELD Mirzakhmedov Saydrasul Shermukhammad ugli specialist of the Namangan branch of the State Institution “Uzbekistan Scientific Testing and Quality Control Center” E-mail: [email protected] ABSTRACT This study focuses on the optimization and application of the reciprocating directdrive electric submersible plunger pump lifting system in the Xinjiang Oilfield. The structural features and operational performance of the system are analyzed to improve oil extraction efficiency while reducing energy consumption. Factors affecting the pump’s stability and performance are investigated, and optimization methods for the drive and control systems are proposed. The results show that the use of a direct-drive system significantly increases efficiency, reduces equipment wear, and lowers operating costs, making it a promising solution for modern oil production. KEYWORDS: reciprocating direct-drive electric submersible plunger pump, optimization, oil extraction efficiency, Xinjiang Oilfield, energy saving, control system, equipment reliability. INTRODUCTION With increasing demands on energy consumption, more low-permeability oil reservoirs are being exploited and developed in China. Usually, the drilled wells in such low-permeability oil reservoirs have a lower productivity, a deeper liquid level, and some even have some curved sections. These factors restrict the pump depth of a conventional sucker rod pumping system and result in a series of problems, such as an increasing pumping unit load, a deteriorating sucker rod stress condition, and increasing eccentric wear between the rod and tubing. To meet the production requirements of low-production, low-pressure reservoirs and deeper wells, many measures and new equipment are being developed and applied in oilfields. A Reciprocating Direct-Drive Electric Submersible Plunger Pump (RDD-ESPP) is a new linear fting system technology and is popularly used in Chinese oilfields because of its Educational Research in Universal Sciences ISSN: 2181-3515 VOLUME 4 | SPECIAL ISSUE 13 | 2025 https://t.me/Erus_uz Multidisciplinary Scientific Journal October, 2025 14 unique characteristics, such as eliminating eccentric wear between the rod and tubing and permitting more advanced automation, variable frequency adjustments, simpler surface facilities, lower maintenance costs, higher efficiencies and its suitability for use in low-production wells [1]. The RDD-ESPP is an innovative rodless pumping method. A linear motor deployed downhole drives the plunger pump up and down, which lifts the formation fluid to the surface. In this way, the intermediate mechanical transmission mechanisms, such as the surface pumping unit and sucker rod, are eliminated. Such a design contributes to improving the lifting efficiency and decreasing the pump energy consumption. In the Daqing oilfield, RDD-ESPPs have been used in 108 oil wells (including 54 vertical wells, 47 deviated wells and 7 horizontal wells). The average pump efficiency is 67.06%, and the average daily power consumption is 57.5 kWh. Compared with a conventional sucker rod pumping system operating at the same production rate, the electricity savings was 45.64% [2-5]. In the Changqing oilfield, a total of 27 oil wells in the low-permeability reservoirs of the Ansai and Longdong areas have adopted this new pumping method since its introduction in 2007. The average pump efficiency increased from 41% to 65%, and the energy savings rate was 22%. The maximum operating period was as much as 813 days [6-8]. In 2011, an RDD-ESPP was used in 5 deviated oil wells in the Zhengting oilfield. These wells have substantial eccentric wear between the rod and tubing, frequent workover and lower production rates when using sucker rod pumping systems. With this RDD-ESPP, the pump efficiency improves by 60.6%, the daily power consumption decreases by 39.9 kWh, and the pump maintenance period is prolonged to 46 days [9]. The Jinlin oilfield has also installed RDD-ESPPs in 11 oil wells by the end of 2014. Here, the average pump and average system efficiencies improved from 25.3% to 79.6% and 9.37% to 16.67%, respectively. The pump maintenance period was extended from 303 days to 503 days and the daily power consumption decreased from 112.7 kWh to 77.6 kWh [10]. The successful application of an RDD-ESPP results in energy savings, improved pump efficiency and significant decreases in the operating costs. However, the operating parameters (such as pump depth, pumping speed and power frequency) of RDD-ESPP lifting systems are mainly determined or adjusted according to the maximum linear motor thrust force and/or by monitoring the operating state in the field. At present, there is no systematic method to guide the design and evaluation of such a system. The primary focus of our study is to develop a theoretical method to determine the optimal working parameters for an RDD-ESPP lifting system and provide a decision process for field operations. Firstly, mathematical models for calculating the wellbore temperature distribution, lifting load, pump efficiency and system efficiency are Educational Research in Universal Sciences ISSN: 2181-3515 VOLUME 4 | SPECIAL ISSUE 13 | 2025 https://t.me/Erus_uz Multidisciplinary Scientific Journal October, 2025 15 developed based on the working principle of the RDD-ESPP and its rodless system configuration. Then, the effects of the pump depth, pump diameter and pumping speed on the lifting efficiency are studied. Finally, the working parameter for low-production and deep wells in the Xinjiang oilfield are optimized and applied. This study provides a theoretical method for selecting the optimal operating parameters for RDD-ESPP lifting systems and analyzes its working state. In this way, we avoid making design decisions by relying solely on field experience. METHODS Mathematical Model. When compared to conventional sucker rod pumping systems and electrical submersible pumping systems, there are some significant differences in the RDD-ESPP lifting system. Therefore, the mathematical models for the lifting design are also different. 1) Compared with conventional sucker rod pumping systems, the RDD-ESPP lifting system does not need a rod string to transfer power. Therefore, the lifting load model and pump efficiency model do not need to consider the effects of rod weight and its elastic stretching and shrinking. 2) Compared with conventional electrical submersible pumping systems, the temperature model only needs to consider the ther mal effects of the motor and cable. 3) The RDD-ESPP pumping system works using an intermittent power supply, meaning that the input power depends on the power supplied during the time required for the upstroke and downstroke. Mathematical Model for Wellbore Temperature. To acquire the temperature distribution in the wellbore, the following assumptions are made. 1) Radial heat losses between the wellbore and the formation are considered and axial heat losses along the wellbore are not included. 2) A steady-state heat transfer system is in existence in the downhole environment. 3) Heat capacity changes in the flowing fluid along the wellbore are very small and this value is taken as a constant. 4) The heat generated by the motor and cable are entirely contribute to heating the fluid. 5) The production rate is assumed to be constant. According to the configuration of the RDD-ESPP lifting system, the wellbore temperature distributions are divided into three parts, namely, from the bottomhole to the motor, the motor and pump body, and from the pump outlet to the wellhead [13, 14]. Bottomhole-to-Motor Section.Using the energy balance equation, the fluid temperature in the bottomhole-to-motor section can be calculated using Eqn. (1): (1) Educational Research in Universal Sciences ISSN: 2181-3515 VOLUME 4 | SPECIAL ISSUE 13 | 2025 https://t.me/Erus_uz Multidisciplinary Scientific Journal October, 2025 16 where, T(h) is the temperature at any location in the bottomhole-to-motor section, °C; t 0 is the surface temperature, °C; α is the geothermal gradient, °C/m; Hw is the reservoir depth, m; h is the depth at any location in the bottomhole-to-motor section, m; Kt is the heat transfer coefficient between the fluid and the formation in the bottomhole-tomotor section, W/(m2·°C); CH is the fluid heat capacity, J/(kg·°C); and G is the fluid mass flow rate, kg/s. Motor and Pump Body (Pump Outlet). The pump outlet temperature is a comprehensive result of motor heating, cable heat dissipation, and heat exchange between the fluid and the formation. It can be calculated using Eqn. (2): (2) Where Tp is the fluid temperature at the pump outlet depth, °C; T(HL) is the fluid temperature resulting from heat exchange between the fluid and the formation at the pump outlet depth and can be calculated by Eqn. (1), °C; HL is the pump outlet depth, m; Nm is the downhole linear motor input power, kW; ηm is the downhole linear motor efficiency, %; Ls is the length of the flat cable attached on the outside of the downhole linear motor, m; I is the working current of the downhole linear motor, A; and R is the resistance per unit length of the flat cable attached on the outside of the downhole linear motor, Ω/m. Pump Outlet-to-Wellhead Section. In this section, the heat transfer includes the heat exchanged between the fluid and the formation, and cable heat dissipation. Similarly, the wellbore temperature at any point can be calculated via the energy balance equation, as expressed in Eqn. (3) and Eqn. (4): (3) (4) where T(hD) is the temperature at any location in the pump outlet-to-wellhead section, °C; hD is the depth at any location in the pump outlet-to-wellhead section, m; KD is the heat transfer coefficient between the fluid and the formation in the pump outlet-towellhead section, W/(m2·°C); and g is gravitational acceleration, which is defined as 9.81 m/s2. RESULTS Sensitivity Analysis and Case Study. From the developed mathematical models, we see that the pump efficiency is mainly affected by the pump depth and produced gas-to-oil ratio, whereas the system efficiency is mainly affected by the time that power Educational Research in Universal Sciences ISSN: 2181-3515 VOLUME 4 | SPECIAL ISSUE 13 | 2025 https://t.me/Erus_uz Multidisciplinary Scientific Journal October, 2025 17 supply is active and the effective lifting head. In the RDD-ESPP lifting system, the working frequency of the downhole linear motor determines the maximum thrust force provided by the motor and the power supply time in the upstroke. The power supply time in the downstroke is usually taken as a constant. However, the working frequency of the downhole linear motor is determined by the maximum lifting load that acts on itself during the upstroke. Thus, the system efficiency is ultimately determined by the pump depth. The pump depth and the produced gas-to-oil ratio determine the fluid properties and pressure difference across the plunger pump. The effects of the pump depth, produced gas-to-oil ratio, pump diameter and pumping speed on the production rate, pump and system efficiencies are analyzed. The parameters used in the analysis are listed in Table 2. Table 2 Model parameters. Parameter Value Reservoir pressure/MPa 35.32 Reservoir depth/m 3617 Reservoir temperature/oC 88.41 Tubing inner diameter/mm 76 Tubing outer diameter /mm 88.9 Casing inner diameter /mm 121.36 Casing outer diameter /mm 139.70 Downhole linear motor WFQYDB 114-1140-(30~50) Water cut/dimensionless 0.148 Oil specific density/ dimensionless 0.839 Water specific density/dimensionless 1.015 Gas specific density/dimensionless 0.65 Bubble pressure/MPa 5.81 Productivity Index/t/d.MPa 1.86 Wellhead tubing pressure/MPa 0.1 Wellhead casing pressure/MPa 0.1 Educational Research in Universal Sciences ISSN: 2181-3515 VOLUME 4 | SPECIAL ISSUE 13 | 2025 https://t.me/Erus_uz Multidisciplinary Scientific Journal October, 2025 18 Figs. (5-7) show the effects of the pump depth and produced gas-to-oil ratio on the production rate, pump efficiency and system efficiency for a stroke of 1.23 m, a speed of 8 rpm and a pump diameter of 32 mm. For higher produced gas-to-oil ratios, the production rate, pump efficiency and system efficiency exhibit an increasingdecreasing change as the pump depth increases. However, for lower produced gas-tooil ratios, these parameters all decrease as the pump depth increases. As the pump depth increases, the gas effect decreases and the pump efficiency increases. However, the pressure difference between the pump inlet and pump outlet increases, which accelerates the pump leakage and leads to a lower pump efficiency. For lower produced gas-to-oil ratios, the pump efficiency is mainly affected by pump leakage. For a constant pump depth, larger produced gas-to-oil ratios produce larger gas effects and, subsequently, lower pump efficiencies. Therefore, the pump efficiency is a comprehensive result of gas and leakage. For a certain produced gas-to-oil ratio, there exists a reasonable range for the pump depth. DISCUSSIONS The pump efficiency and system efficiency can be improved largely by adopting this new RDD-ESPP lifting system and changing the pump depth. For the same stroke, speed and pump diameter, we observed that a large increase in the pump depth could not significantly improve the lifting efficiency. Considering that increasing the pump depth will increase the tubing and cable cost, a pump depth of 1950 m, a pump diameter of 38 mm, a stroke of 1.23 m and a speed of 2 rpm were adopted. The currents and frequencies for the upstroke and downstroke were 25 A and 12 A, and 8 Hz and 20 Hz, respectively. Using these optimized working parameters, a daily production rate of 2.8 t/d, a power consumption of 86.39 kWh per ton of liquid and a system efficiency of 4.97% were achieved in the X-I well after the RDD-ESPP lifting system was installed. The lower system efficiency is due to the installation of an unsuitable motor due to limitations of the supply of motors in the field. The daily power consumption decreased from 363.8 kWh to 241.9 kWh after optimization and a power savings rate of 33.5% was realized. The pump efficiency increased from 38.9% for the sucker rod pumping system to 80.5% for the RDD-ESPP lifting system. Compared with other field applications by changing the sucker rod pumping system to an RDD-ESPP lifting system, average pump efficiency improvements such as 44.3% in the Jinlin oilfield (Zhang, 2015) and 60.6% in Zhengting oilfield (Wang, 2012), 22% in the Changqing oilfield (Zheng et al., 2013) and 45.64% in the Daqing oilfield (Wang et al., 2007) were achieved. The application of the RDD-ESPP lifting system in the X-I well is demonstrated to have a remarkable energy-savings effect. Additionally, errors between the calculated results and the actual measurements of the production rate, pump Educational Research in Universal Sciences ISSN: 2181-3515 VOLUME 4 | SPECIAL ISSUE 13 | 2025 https://t.me/Erus_uz Multidisciplinary Scientific Journal October, 2025 19 efficiency, system efficiency and power consumption are 7.14%, 7.55%, 9.46% and - 5.98%, respectively. These results show that the proposed method can be used to select optimal operating parameters for a RDD-ESPP lifting system and analyze its working state. CONCLUSION A reciprocating direct-drive electric submersible plunger pump lifting system is a new rodless artificial lifting system with a higher pump efficiency and a lower power consumption. Based on the working principle of this system, mathematical models for the wellbore temperature distribution, lifting load, pump efficiency, system efficiency and tubing strength validation are developed. Field applications were implemented based on the proposed method and the following conclusions can be drawn: (1) The RDD-ESPP lifting system completely eliminates the problem of eccentric wear between the tubing and the sucker rod that occurred in conventional sucker rod pumping systems. This technology can be used in vertical, deviated and horizontal wells. Moreover, it has a lower power consumption and a higher system efficiency than a conventional sucker rod pumping system due to the use of an intermittent power supply. (2) The pump efficiency of the RDD-ESPP lifting system is mainly affected by the gas and leakage. As the pump submergence depth decreases, the gas effect in the pump and the pressure difference across pump increase, which causes the pump leakage to increase and the pump efficiency to decrease. 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