Development of the Subsurface Process and Reinjection Compressor

This paper discusses component developments, validation testing, and yard testing of the subsurface process and reinjection compressor (SPARC) prototype tool approaching downhole flowing conditions (≈1200 psig and > 225°F). This is the first time a compressor and turbo expander have been built small enough to be run through tubing and operated autonomously from the surface. A brief review of the overall system design and critical component design and testing are followed by a detailed review of the surface testing of the entire prototype machine at simulated downhole conditions. The SPARC concept uses the excess production pressure (energy) that is usually wasted across a choke or elsewhere in the production system to generate power through a downhole turbo-expander that runs a downhole gas compressor to reinject a portion of the gas stream. The system consists of a downhole separator, compressor, turbo-expander and other standard downhole equipment for the necessary plumbing. The successful test results of the bearing and thrust disk component testing at up to 1,000 psig and > 450°F are provided, followed by the successful yard test results of the entire SPARC prototype machine at downhole flowing conditions, including all the rotating equipment (turbo expander, compressor, and shaft), in situ process-lubrication system, and autonomous controls. This equipment will allow for the reduction of costly surface facilities to process, compress, and reinject produced gas into North Slope fields and some oil and condensate fields elsewhere globally, which are limited in liquid hydrocarbon production because of surface gas processing facility limitations. Another potential use of the SPARC technology is as an artificial lift mechanism for gas reservoirs. Using the SPARC as a gas well artificial lift system would require a redesign of the SPARC with an electric motor as its power source in place of the turbo-expander. However, no new technology breakthroughs are necessary because the technology has already been developed with the SPARC design. To date, there have been no small gas compressors, turbo expanders, and other necessary equipment built and tested that can be run through 4 1/2-in. tubing/casing and operate autonomously at downhole conditions. This technology opens up the possibilities of additional relatively inexpensive gas recycling on the North Slope and other condensate fields worldwide.