Study on transient flow behaviors in a three-stage helico-axial multiphase pump under slug flow condition from wellhead

Oilfield recovery often has extreme flow patterns of slug flow, and its gas volume fraction (GVF) still fluctuates strongly after being buffered by a homogenizer. After entering the multiphase pump, it causes transient fluctuations in pump performance, which challenges the stable operation of the multiphase pump. This paper simulates the flow field in a three-stage multiphase pump using the Euler-Euler two-fluid model and the shear stress transport k-omega (SST k - omega) turbulence model with the buffered slug flow as the boundary conditions. The results show that the differential pressure and torque of each impeller vary with the fluctuation of the inlet gas volume fraction (IGVF) and the maximum fluctuation rate reaches 36.48% and 32.97%, respectively; the maximum fluctuation rate of axial force and radial force is 1.02% and 51.18%, respectively, and the buffered slug flow has limited effect on the axial force. The main factor of pressure pulsation is the fluctuation of GVF flow and the interaction of static and dynamic. The main frequency in the impeller is the fluctuation frequency of the GVF or the diffuser blade frequency. The main frequency in the diffuser is the impeller blade frequency and its double frequency. The fluctuation frequency of the GVF is the secondary frequency, and the amplitude is relatively stable.