Terrain Induced Slugging

Santos Ltd Adelaide, South Australia

Industry contact:  Mr. Tung Nguyen  (tung.nguyen@santos.com)

Moderators:

Prof. Robert McKibbin  Massey University  NZ  (r.mckibbin@massey.ac.nz)

Multiphase pipelines frequently experiences liquid slugging caused by a number of mechanisms.  One of these is influenced by the topography of the pipeline which normally includes many uphill and downhill sections.

Typically, liquids enter a downhill section and accumulate at the bottom of the section until gas flow is blocked.  Line pressure will then rise until the liquid head is overcome and the liquid plug is blown into the following sections.  This effect cascades all the way to the pipeline outlet.  Typically, liquid outflow would rise and flow in a fairly well defined cyclic pattern, with peak flows up to ten times the calculated steady-state flow.

Terrain-induced slugging presents a challenge for pipeline design engineers.  The liquid slugs have to be dealt with to prevent upsets to processing facilities downstream of the pipeline outlet.

Some theoretical work had been done on this kind of slugging and the references are as follows.

1.      De Henau V & Raithby G D (1995), “A Transient Two-Fluid Model for The Simulation of Slug Flow in Pipelines – I. Theory”, International Journal of Multiphase Flow, Vol. 21, No 3, pp. 335-349.

2.      De Henau V & Raithby G D (1995), “A Transient Two-Fluid Model for The Simulation of Slug Flow in Pipelines – II. Validation”, International Journal of Multiphase Flow, Vol. 21, No 3, pp. 351-363.

3.      De Henau V & Raithby G D (1995), “A Study of Terrain-Induced Slugging in Two-Phase Flow Pipelines”, International Journal of Multiphase Flow, Vol. 21, No 3, pp. 365-379.

Commercial softwares have the capabilities of simulating terrain-induced slugging such as SimSci’s TACITE, Hyprotech’s ProFES but they are very expensive to acquire.

The aim of the study should be to come up with simple equations to estimate the peak liquid flow and the peak-to-peak flow period.