Qualification of a Subsea Pump for Dense Phase Fluid Applications in Brazilian Deep-Water Pre-Salt Fields

Le résumé fourni par la source

Abstract An extensive de-risking program was conducted to qualify the subsea dense gas pump project design. As part of this program, a subsea pump prototype, a back-to-back centrifugal pump, was designed, constructed, and evaluated using a dense CO2/N2 mixture, referred to as dense gas. This dense fluid has a gas-like viscosity, but a density closer to that of a liquid. The pump prototype was evaluated at varying suction pressures ranging from 150 to 200 bar, up to a maximum discharge pressure of 350 bar. The machine was operated at a maximum speed of 6,000 rpm, delivering a flow rate of up to 700 m3/h of gas mixture. The composition and pressure of the working fluid was selected to simulate Brazilian Pre-salt field conditions at the seabed. A vertical integrated pump-motor unit with environmentally friendly barrier fluid (BF) was configured using radial centrifugal impellers in a similar fashion as a multiphase subsea booster, to pump the homogeneous dense mixture. The main objectives of the test campaign were to validate the hydraulic performance prediction and assess the rotordynamic behavior of the pump when operated with a dense fluid. Additionally, a series of slug tests were performed to prove the robustness of the pump in case of the transient high-load scenarios. The pump passed all the required tests and demonstrated anticipated robustness, which is crucial for subsea operation. The measured hydraulic performance exceeded predictions at high-load, high-speed conditions, which may be partly attributed to the conservatism in the selection process. The successful combination of hydraulic performance, robust rotordynamic behavior, and an efficient control strategy provides strong evidence for the viability and effectiveness of the current subsea pump design for dense gas application.

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