Use of gas-turbine engines in oil field pumping units

Abstract

Modern oil field pumping units for hydraulic fracturing of formations, in particular deep-penetration fracturing, typically have high power outputs. The unit, which is mounted on a truck chassis, consists of an engine, transmission, primary actuating mechanism (high-pressure pump), manifold, and other equipment. Diesels with power of 700-1500 kW are used as the drive engine for these units; the operating indexes of diesels vary sharply with load, dropping off when the load is increased only slightly. Pumping units do not operate under steady conditions. The injection pressure for pumping units will depend on the formation pressure, the physical properties of the formation, the well depth, the diameter of the well string through which the fracturing fluid and the sand mix are pumped, the fluid delivery rate, and so on. At the start of the operation, as the fracturing fluid and the sand mix are pumped, the fluid delivery rate, and so on. At the start of the operation, as the fracturing fluid is injected, the pressure on the pumping unit increases. Then, at the moment of fracturing the formation, the pressure drops off sharply and will vary, depending on the hydraulic resistances to movement of the sand mix and injection fluidmore » in the pipe and in the bottom-hole zone of the formation. Gas-turbine engines with a free turbine are more effective as the drive for pumping units. The first attempt to use a gas-turbine engine was made in the mid-1960s. At that time, however, the work was limited to the development of a rough design, in view of the great length of the AI-23 engine and, most important, its cost. In recent years, free-turbine gas engines have been designed and manufactured commercially as the drive for transport vehicles. The characteristics of these engines match the requirements for use in pumping units. Gas-turbine engines have the advantages over diesels. These advantages are discussed.« less