An Engine Driven, High Pressure Reciprocating Type Injection Gas Compressor Design
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A 10,000 psi high pressure natural gas injection compressor train was procured, manufactured, tested and installed in the Boquerón production facility in Eastern Venezuela. The injection machinery consisted of three (3) parallel slow speed reciprocating gas compressors each driven by a natural gas driven internal combustion engine through a speed reducing gearbox. The equipment had been purchased in an early phase of the project by the original oil company, so it could not be changed. Due to the critical timing of compression required to maintain reservoir pressure and incremental oil recovery, the equipment could not be changed without large financial consequences. After preliminary review of the purchased equipment, it was recognized early by the engineer, procure, and construct (EPC) design engineering team that the compressor type and selection including the design were not the preferred arrangement. However, due to schedule and contract constraints the selection and design could not be significantly changed. Although the compressor itself was considered properly selected there was considerable attention given to the drive train. This drive train consisted of the internal combustion engine, a gearbox, a steel torque shaft that connected the gearbox to the compressor and an intermediate bearing/bearing support. As the project progressed there were significant design improvements made to improve the safety, operation, and life of the compressor train. The initial design of the torque shaft indicated that it would fail every time the machinery experienced a shutdown. In order to overcome such a failure the drive train included a special coupling with shear bolts that would shear every time the compressor train had shut down, the function of which was to prevent the torque shaft from fatigue failure. Shearing bolts during every shutdown was not considered safe or acceptable operating practice. During the course of the project, there were significant improvements made, first to the torque shaft, and then to the coupling connecting the gearbox to the torque shaft, then to the coupling between the engine and high speed gear pinion. The torsional characteristics were improved significantly with the upgrades and design improvements. After installation, extensive field testing was conducted on each injection gas compressor to ascertain the torsional characteristics of the drive train, including stresses in critical components during the shutdown events. The data confirmed that the torque shaft was in fact designed for infinite life and would not fail from material fatigue as was feared initially. During the design phases engineering consultants were contracted to perform torsional studies to confirm the torsional critical speeds initially predicted by the compressor manufacturer. After installation the same consultant used strain gauges to measure the torsional shear stresses and the torsional critical speeds. There was an enormous amount of valuable engineering data generated during the design verification process and field testing. The authors feel that this information should be shared with others in the oil and gas industry when considering this type of machinery and machinery train for their high pressure injection gas compressor services or projects.
Ehlers, Gary A.; Haaland, Kurt (2010). An Engine Driven, High Pressure Reciprocating Type Injection Gas Compressor Design. Texas A&M University. Turbomachinery Laboratories. Available electronically from