Electric Submersible Screw Pump (ESSP) is a hybrid system that combines the features of a screw pump (PCP) and an electric submersible pump (ESP), making it highly suitable for horizontal well applications. As a rodless pumping system, it eliminates friction losses between tubing and rods, enhancing overall efficiency. The screw pump is particularly effective in handling sand-laden formations, which makes it ideal for environments like the Kulin horizontal well project. The Kulin project began in early 2002 and was completed by December 2003. The first horizontal well, Kulin082 (KL082), and the second, Kulin083 (KL083), were both equipped with ESSPs for artificial lift. KL082 initially produced 708 barrels of liquid per day, with 531 barrels of oil and a 25% water cut. KL083 had a daily production of 518 barrels of liquid, including 394 barrels of oil and a 24% water cut. Given the unconsolidated sand in the nearby Duri field, traditional rod pumps faced significant challenges due to sand production, which reduced their efficiency. In horizontal wells, it's also difficult to manage sand using conventional screen pipes. Therefore, the ESSP was chosen for its sand-tolerant design and rodless operation. Although screw pumps are not typically used in horizontal wells, and ESPs struggle with sand, the ESSP proved to be the best solution for this specific scenario. The ESSPs installed in the Kulin wells operated in 9 5/8-inch production intervals with straight sections having well slopes below 2° per 100 feet. The stator rubber in the screw pump was designed to function within a temperature range of 135–150°F, which was lower than the maximum allowable limit. The flow rate and pump efficiency were controlled using ground-based variable speed drives (VSDs). The output from these two horizontal wells was significantly higher—2.5 to 3.5 times greater than that of vertical wells in the same area. The ESSP system uses an electric submersible pump as the downhole drive mechanism. The rotor inside the stator rotates, creating a pumping action. The rotor is made of stainless steel with a chrome-plated surface to resist corrosion. Manufacturers offer different stator rubber options based on bottom-hole temperatures, with standard ratings up to 95°C (203°F), 105°C (221°F), 135°C (275°F), and 150°C (302°F). Given the bottom-hole temperature of approximately 65.6°C, the 95°C (203°F) rated product was selected. Additionally, compatibility of the rubber with aromatic hydrocarbons in the fluid was considered. The motor size was determined based on the power required for starting the pump, casing dimensions, and bottom-hole temperature. The gear reducer provides the necessary speed and torque for the screw pump, while the seal prevents fluids from entering the gear unit and motor. A flexible shaft transfers the rotation from the seal shaft to the screw pump, ensuring smooth operation. Installation of the ESSP in KL082 occurred at a depth of 1,440 feet, with a true vertical depth of 1,267 feet and an inclination of 64 degrees, resulting in a well slope of 1.6° per 100 feet. For KL083, the pump was installed at 1,014 feet deep, with a true vertical depth of 891 feet and an inclination of 58 degrees, giving a slope of 1.5° per 100 feet. A 3 1/2-inch tubing was used, along with a 3 1/2-inch control valve and a mixing valve placed 90 feet above the pump. A cable protector was also installed to prevent damage from cable friction. The ESSP motors operated at 2,333 rpm, with a gear reduction ratio of 9:1, resulting in a pump speed of 259 rpm and a flow rate of 881 barrels per day. In the field, the ESSP in KL082 operated for 800 days with an average pump efficiency of 66%, showing no signs of failure. Some initial issues, such as possible blockage at the inlet, were resolved through reverse rotation, and normal operations resumed. KL083’s ESSP ran for 450 days with an average efficiency of 56%, without any downtime due to pump failure. **Conclusions:** (1) ESSPs combine the advantages of ESPs and PCPs, making them ideal for horizontal wells. They offer high production efficiency, even for viscous fluids with high solids content; eliminate friction losses by being rodless; avoid surface oil spills with no packing box; provide high torque; and allow motor-driven backwashing. (2) The average pump efficiency of the ESSP in the Kulin wells ranged from 56% to 66%, far exceeding the less than 30% efficiency of rod pumps in similar Duri field horizontal wells. (3) The long operational life of the ESSP is evident in the performance of KL082 and KL083. By June 2004, KL082 had been operating continuously for over 800 days, while KL083 had been running for more than 450 days.

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