Subsurface Compressor System Improves Gas Production in Unconventional Reservoirs

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 201138, “Liquid Removal To Improve Gas Production and Recoverable Reserves in Unconventional Liquid-Rich Reservoirs by Subsurface Wet Gas Compression,” by Lukas Nader, SPE, David Biddick, SPE, and Herman Artinian, SPE, Upwing Energy, et al., prepared for the 2020 SPE Virtual Artificial Lift Conference and Exhibition—Americas, 10–12 November. The paper has not been peer reviewed. This paper describes an artificial lift technology, a subsurface compressor system (SCS), that simultaneously removes liquids, increases gas production, and improves recoverable reserves in gas wells. The subsurface compressor can reverse the vicious cycle of liquid loading, which decreases gas production from a gas well and leads to premature abandonment, by creating a virtuous cycle of increased gas and condensate production. The first field trial of the technology in an unconventional shale gas well supports the mechanism of subsurface gas compression and its benefit to unconventional gas production. The SCS This paper focuses on the latest deployed design. As with all SCS systems, this unit has three major components (Fig. 1). High-Speed Motor. The motor is a four-pole, high-speed, permanent-magnet (PM) synchronous topology. The motor maximum operating speed is 50,000 rev/min, with a 55,000-rev/min overspeed. Surface-mounted PMs are retained on the shaft surface. A sine filter is also used to minimize harmonic losses in the rotor, eliminating the need for active cooling flow in the rotor cavity. With the motor housing hermetically sealed from the environment and maintaining a low pressure within the housing, a minimum life of 20 years is expected from the electrical motor section. The motor rotor is levitated with passive magnetic bearings, requiring no lubrication or a pressurized air source, to support the high-speed rotating shafts. Magnetic Coupling. The magnetic coupling consists of three major components: the male and female ends of the magnetic coupling as well as the isolation can in between. The female end of the magnetic coupling is attached directly to the motor. The isolation can is used to seal the female magnetic coupling section hermetically within the body of the PM motor from the environment. Using a magnetic coupling to transmit torque through an isolation can is one of the key features of the protectorless, rotating, sealless motor system to ensure reliability of the motor. Hybrid Wet Gas Compressor. The compressor is a multistage hybrid axial flow wet compressor. The key advantage of this proprietary compressor design is its relatively straight flow path compared with those of centrifugal compressors. When the flow path is straight, with little change of direction, the heavier constituents, including liquids and solids, will follow the gas phase because there is little or no centrifugal force to separate the high-density phases from the low-density one. Also, erosion of the compressor parts is minimized by the straight flow pattern because of the lower probability of impingements of solid particles on the compressor internal surfaces compared with the torturous internal paths of centrifugal compressors. The remainder of the system, as well as the deployment, is very similar to an electrical submersible pump.