Operational Problems with 8,000-psig Injection Compressors
Authors: Cornell G.L. 
Published: December 2007

High-speed compressors can be used successfully in high-pressure gas injection service. To achieve satisfactory results, however, closer than usual attention must be given to the gas properties at the high pressures and to the over-all design of the unit. pressures and to the over-all design of the unit. The Field Situation
The Cheniere Cadeville Unit is located in Ouachita Parish, La., about 15 miles west of Monroe. The Parish, La., about 15 miles west of Monroe. The field was unitized in 1966 for the purpose of conducting cycling operations, with Pan American Petroleum Corp. (now Amoco Production Co.) as the Petroleum Corp. (now Amoco Production Co.) as the operator. Because of the configuration of the field14 miles long by about a mile wideit was necessary to install a rather unusual gas gathering and injection system. A long header was installed through the center of the field with each of the producing wells tied into the header by means of laterals. The injection compressors were located at the injection well sites, two on the east end of the field and three on the west. Gas is supplied to the compressors through the production header.

High-Speed Machinery
During the studies of the cycling project, it became apparent that the injection pressure would be extremely high, approaching 8,000 psig; consequently, bids for the compressor were solicited using this as a design discharge pressure. The design suction pressure was 1,500 psig, and the required injection volume was about 4,200 Mcf/D/well. An analysis of the quotations received showed that the cost of five highspeed (1,000 rpm), direct-connected, skid-mounted compressors was considerably less than comparable low-speed (300 to 400 rpm) integral machinery. Although there were no machines of this type running in such high-pressure service, the difference in cost made it attractive to use the high-speed machinery. The compressors selected were equipped with 4 two-stage "tandem" cylinders each. In this arrangement, the compressor piston rod and the pistons are constructed in one piece. The first stage pistons are constructed in one piece. The first stage of compression is performed on the crank end of the cylinder. A "dead space" between the two pistons is subjected to firststage suction pressure (Fig. 1). The first compressor was ready for start-up Feb. 9, 1967. Almost immediately upon loading, a problem developed with one of the compressor crossheads. problem developed with one of the compressor crossheads. Upon disassembly, it was determined that the crosshead pin bearing had failed. A second machine was ready to pin bearing had failed. A second machine was ready to start up and operations were shifted to that unit while repairs to Number One was undertaken. However, upon start-up of the second machine, the same problem appeared on a crosshead on this machine. Operations were suspended until rod loads could be recalculated, compressor loading procedures reviewed, and a revised design for the procedures reviewed, and a revised design for the crosshead pin bearing developed.

Rod Loads
Upon further consultation with the manufacturer, it was determined that the calculated rod loads of about 12,000 lb in compression and 3,000 lb in tension did not take into account the inertial effect of the weight of the connecting rod, crosshead, piston, and rod. As a consequence, thens was actually a nonreversing rod load; that is, the rod was always in compression.
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