The hydraulic characteristics of an industrial jet pump were determined in single and two-phase flow, and a prototype was studied to determine geometric shapes well suited for two-phase flows. Jet pumps were then compared to other downhole pumps from the technical and economic standpoint.
Jet pumps are known in chemical engineering as being able to pump any sort of fluid. They are used for downhole pumping because of their simplicity, ruggedness, flexibility of use and ease of maintenance. Several thousand wells are equipped with jet pumps, mainly in the United States, but their implementation remains limited to cases of difficult production (deep well hot or corrosive crudes, production of sand or formation of deposits, etc.). It may seem surprising that their use is not spreading faster. Actually, there are two major related reasons for this:
Their energy efficiency is reputed to below. For petroleum jet pumps the typical efficiencies announced range from 26 to 33%.
Sizing methods are often considered as inaccurate, incomplete and somewhat mysterious. Models developed by experimenters in a restricted parametric range of geometric shapes, flow rates, pressures and fluid natures, cannot be generalized to all jet pumps and all operating conditions. Formulations may diverge, depending on the simplifying hypotheses retained, thus giving discordant results. Lastly, there is no tried-and-true design method in two-phase pumping conditions.
Therefore, for a long time, producers remained dependent on manufacturers for the sizing of their jet pumps and for defining suitable equipment for processing fluids on the surface for a given production time. in such a context, there is no assurance that such pumps have always been used under optimal conditions.
In-depth research on multiphase flows through flowlines and production tubings has been done in the last ten years by the IFP, Elf-Aquitaine and Total-CFP association. In addition, IFP is working on various two-phase pumping processes, particularly by jet pumps, for subsea production applications. The present project has the threefold goal of:
Optimizing geometric shapes of pumps to improve their energy efficiency by a series of test-bench experiments.
Developing a precision computer model capable of forecasting the operational characteristics of jet pumps having various shapes, for both single-phase and two-phase flow.
Determining their scope of use by developing technical and economic computing methods for the principal downhole pumping processes.
Jet pumps operate on the principle of the venturi tube. A high-pressure driving fluid is ejected at high speed through a nozzle, thus creating a depression enabling the fluid to be sucked up and entrained in a cylindric mixing tube (throat) where the velocities are homogenized. A conical diffuser then converts the kinetic energy of the mixture into pressure (Fig. 1).