A Comprehensive Study of a Novel Submersible Pump

Abstract

Abstract Electric submersible pumps (ESPs) are over a century-old technology. As reservoirs mature, water cut increases, motor electric load increases which in turn, increases the required equipment size, mainly the pump and motor lengths. In addition, in alternative ESP deployment methods, length of the ESP is a critical factor during installation and retrieval due to crane limitations especially for offshore. To mitigate the downhole assembly length, a novel motor and pump system is designed. The primary advantage of this design is manifested by the elimination of the protector section that represents a problematic component in a typical electric submersible pump (ESP). This study focuses on the feasibility assessment of the concept at given conditions, where the motor and the pump are integrated concentrically in one unit inside a cylindrical housing in an arrangement suitable for downhole. A comprehensive system design involving electrical, mechanical and hydraulic analysis was carried out to develop a Permanent Magnet Pump (PMP) with performance characteristics matching a typical conventional ESP. A number of factors affecting the new ESP system were considered. They include maximum radial dimension constraint, high flow rate and total dynamic head requirements, motor cooling, the need to maintain reasonably high efficiency over a wide range of flow rates, sand and gas handling, and finally the ease of manufacturing and system assembly. An architecture based on a labyrinth screw pump was found to be the most appropriate one for use in the 562 series motorized pump design. Detailed calculations on pump and motor were conducted to determine the system dimensions and performances. For typical field applications with rates ranging from 4000 to 5000 BPD and total dynamic heads ranging from 3000 to 4000 ft, a system made of forty-five stages with an approximate length of 45 ft was found to be sufficient. The PMP overall efficiency ranged from 52% to 58% while the operating speed ranged from 3700 to 4500 RPM. Motor cooling was achieved by circulating part of the pumped fluid back to the pump suction side through the air gap. The fluid temperature increase ranged from 20°F to 30°F, when brine is the pumped fluid. This comprehensive work assessed the feasibility of developing a novel, motorized pump for downhole artificial lift applications. It is clearly shown that this new ESP architecture is feasible and practical. With this new design, a next generation of ESPs can be built without the conventional motor seal/protector sections, eliminating one of frequent failure components. In addition, the ESP overall length can be shortened, paving the way to develop a more compact, rigless ESP deployment and retrieval technology for further reduction in operational cost and production deferral.