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Electric submersible screw pump (ESPCP) for use in Kulin horizontal wells
Electric submersible screw pumps (ESSPs) combine the features of a progressing cavity pump (PCP) and an electric submersible pump (ESP), forming an efficient downhole fluid lifting system ideal for horizontal wells. This rodless pump design eliminates friction losses between rods and tubing, making it highly suitable for challenging environments. The Kulin horizontal well project, initiated in early 2002 and completed by December 2003, included two wells: Kulin082 (KL082) and Kulin083 (KL083). After project completion, ESSPs were deployed for artificial lift. KL082 initially produced 708 barrels of liquid and 531 barrels of oil daily with a 25% water cut, while KL083 produced 518 barrels of liquid and 394 barrels of oil with a 24% water cut.
Given the unconsolidated sand in the adjacent Duri field, sand production significantly reduced the efficiency of rod pumps, and traditional screen pipes were ineffective in controlling sand in horizontal wells. Therefore, a sand-tolerant, rodless pumping system was chosen. Although screw pumps are typically not used in horizontal wells and ESPs struggle with sand, the ESSP proved to be the best option.
ESSPs installed in Kulin’s horizontal wells operated in 9 5/8-inch production intervals with well slopes below 2° per 100 feet. The stator rubber functioned within a temperature range of 135–150°F, which is below its maximum limit. Flow and pump efficiency were managed via ground-based variable speed drives (VSDs). These horizontal wells achieved output 2.5 to 3.5 times higher than vertical wells in the same area.
**1. Electric Submersible Screw Pump Design**
The ESSP uses an ESP as the downhole drive system. The rotor rotates inside the stator, creating a pumping action. The rotor is made of stainless steel with a chrome-plated surface for corrosion resistance. Manufacturers offer different stator rubber temperature ratings—up to 95°C (203°F), 105°C (221°F), 135°C (275°F), and 150°C (302°F)—based on bottom-hole conditions. Since the bottom-hole temperature was around 65.6°C, the 95°C-rated product was selected. Compatibility of the rubber with aromatic hydrocarbons in the fluid was also considered. Motor size depends on starting power, casing size, and bottom-hole temperature. A gear reducer adjusts speed and torque, while a seal prevents fluid from entering the motor and gear unit. A flexible shaft transfers rotation into the required torque for the screw pump.
**2. Electric Submersible Screw Pump Installation**
ESSPs are typically installed in straight sections with well slopes up to 15° per 100 feet. In KL082, the pump was installed at 1,440 ft depth with a true vertical depth of 1,267 ft and an inclination of 64°, with a slope of 1.6° per 100 ft. KL083 was installed at 1,014 ft depth, with a true vertical depth of 891 ft and an inclination of 58°, with a slope of 1.5° per 100 ft using 3 1/2-inch tubing. A 3 1/2-inch control and mixing valve were installed 90 ft above the pump, and a cable protector was added to prevent cable wear. Two ESSP motors operated at 2,333 rpm, with a gear ratio of 9:1, resulting in a pump speed of 259 rpm and a flow rate of 881 barrels per day.
**3. Field Application**
KL082’s ESSP operated for 800 days with an average pump efficiency of 66%, showing no signs of failure. Some initial issues were resolved through reverse washing via the motor. KL083’s ESSP ran for 450 days with an average efficiency of 56%, and no downtime occurred due to pump failures.
**4. Conclusion**
(1) ESSPs combine ESP and PCP technologies, offering several advantages for horizontal wells: high efficiency even with viscous, high-solid fluids; elimination of rod and tube friction; no packing box to prevent surface oil spills; high torque; and the ability to perform reverse washes.
(2) The average pump efficiency of Kulin’s ESSPs ranged from 56% to 66%, far exceeding the less than 30% efficiency of rod pumps in Duri’s horizontal wells.
(3) The long operational life of ESSPs is evident in KL082 and KL083. As of June 2004, KL082 had been stable for over 800 days, and KL083 had operated for more than 450 days.