The Neptunia Multiphase Pump: Test Results and Applications

Abstract

ABSTRACT A multiphase pump known as Neptunia has been developed and constructed by Cotap-Neptunia over the last three years. This article presents the main design features of the pump, its calculated performances and test loop measured performances, and the advantages of itsuse both for on-shore and for topside or subsea offshore applications. MULTIPHASE PUMPING Oil companies worldwide are more and more attracted to the use of multiphase pumps for boosting multiphase flow. Their main advantage is that the currently employed system of separating the liquid and gaseous phases, involving the use of bulky separators, fluid pumps, gas compressors and often two pipelines, one for the gas and one for the fluid, is no longer necessary. On shore, the separation installations can be replaced by multiphase pumps which make for a simpler, more compact and less costly system. For off-shore platforms, the use of multiphase pumping can prolong the production of depleting wells through decreasing pressure at the wellhead. These wells are often already exploited by the use of gas-lift. However, the long distances between the wells and the effluent processing installations induce high head losses on-line and limit the production flow rates. By using the multiphase pump, it is possible to increase the two-phase effluent flow rate by decreasing the wellhead pressure, thus optimizing efficiency by increasing its service life. Platforms often have enough space available to install these pumps; however, the problem is often that there is either no energy or insufficient energy available to drive them. The excess gas produced, which is often burned off, could be used to power gas turbines orgas diesel engines for this purpose. The production from North Sea Gulf of Mexico or Off-shore Brasil satellite wells can be made profitable by using a means of transportingmultiphase effluents from these wells to the existing processing platforms, Subsea multiphase pumps can be used to exploit reserves at great depths (from 1000 to 2000 m) and to transport the mixture from the well outlet over long distances (up to approximately 50 km), thereby avoiding the need to construct costly platforms. The use of subsea pumps requires the implementation of a highly reliable technology (2 years MTBF), which means h must be simple, sturdy and proven. Since its conception in 1991, the Neptunia multiphase pump has been designed to ally strength with a high degree of reliability. It is based on the route dynamic technology with an open axial hydraulic design allowing it to pump widely varying mixturesincluding solid particles without the risk of mechanical failures. Since this technology is highly sensitive to the mean density of the mixture, it is necessary to use variable-speed drive systems and to achieve the best possible homogeneity of the mixture at the pump inlet, factors which also contribute to the overall reliability of the system. THE NEPTUNIA PUMP The Neptunia multiphase pump (see figure 1) was developed by Cotap-Neptunia in 1991-1992 in the laboratories of Technicatome, a French company specializing in prime contractor ship of nuclear boilers for the French Navy fleet.