Enhanced Multiphase Flow Predictions in Twin-screw Pumps

In oil field applications it is often required to pump oil, gas, and water as mixtures rather than separating the fluid. Although the performance prediction of twin-screw pumps on liquids is well established, the prediction of performance of these pumps on multiphase mixtures presents a challenge. Test data of twin-screw rotary pumps are compared with predictions of performance over ranges of fluid viscosity and intake gas void fraction (GVF) from zero to 100 percent. The prediction method includes the effects of internal clearances, which can vary spatially, pressure distribution, laminar and turbulent internal leakage or “slip” flow, and viscous heating of the slip flow. The method predicts the experimentally observed variation of pump intake volume flow rate as pump pressure rise increases, namely: • The traditional straight-line decrease for highly viscous, laminar, pure-liquid flow; • The initially rapid decrease for low-viscosity, turbulent, pureliquid flow; and • The negligible decrease at high GVF and pressure ratio for all viscosities. This ability to more accurately predict pump performance for the many combinations of operating conditions has enabled pump manufacturers to more accurately design the multiphase pump required for the intended duty.