Application of Stirling-Cycle Generators in Production Operations

Abstract

Summary Clean, inexpensive, and reliable on-site electric power generation for remote wellsites is an emerging need. There is a growing demand for electric power sources in the range of ½ to 1.5 kW to run pumping units and pumps on liquid loaded gas wells. To understand one possible option, a pilot project consisting of three 0.8-kW Stirling cycle electric generators was conducted in Wyoming. One generator was installed driving a conventional beam pump at the US Department of Energy's (DOE) Rocky Mountain Oilfield Testing Center (RMOTC). Two generators were installed for telemetry power service on well pads in the Wamsutter gas field. In addition to these two applications, small gas-fired generators could provide power for cathodic protection, chemical dosing systems, and other low-rate pumping requirements. The pilot demonstrated that a Stirling cycle generator can pump a small well and provide supervisory control and data acquisition (SCADA) power even in cold weather conditions. A simple fuel-control and conditioning system provided reliable operation when properly installed. Operations and maintenance observations from the 1-year pilot are presented. Stirling cycle engines are external combustion engines which offer some advantages over traditional internal combustion engines: lower maintenance cost, low NOx emissions, and the recovery of heat for process uses. In fact, the current commercial equipment is best thought of as a ¾-kW cogeneration unit. Introduction The combination of higher oil and gas prices over the past decade coupled with increasing concern over greenhouse gas emissions has increased the incentive for well operators to use electric-driven production equipment located at the wellsite. In many cases, wells are located far from the traditional electric utility and a remote power source is required. At this time, there are few options to provide the electric power in the ½- to 1.5-kW range at remote wellsites. Services that can be improved using electric power at wellsites include beam pumping, chemical injection, cathodic protection, and SCADA. In addition, there are potential future services such as gas well deliquification (Dotson et al. 2006) or tank vapor recovery which could be enabled by electric power. To investigate the potential of a small, low maintenance gas-fired electric generator, three Stirling cycle electric generators were installed in Wyoming. This paper will outline the alternatives available for low power generation at wellsites. This paper will also show how a gas-fired generator fits into the mix, and why a Stirling cycle generator was selected for testing. The Stirling cycle will be briefly described, followed by the design for power storage and fuel gas supply for the Wyoming installations. The results from both SCADA and well-pumping applications will be provided, along with the overall conclusions from the test.