Transient gas-liquid flow phenomena in M-shaped jumper of subsea gas production systems during start-up operation

Abstract

Removal of the accumulated liquid from jumpers of subsea gas production systems is essential to avoid possible hydrate creation and further damage to the pipeline. However, the displacement of high amounts of accumulated liquid during the production start-up leads to a gas pressure rise. Liquid plugs formed during the liquid displacement impact the structure's elbows. This, in addition to cyclic pressure/forces fluctuations, may lead to harmful flow-induced vibrations (FIV). These flow phenomena that may endanger the jumper structure were explored in air-water experiments performed in a lab-scale jumper. The critical (minimal) gas velocity needed to purge the accumulated liquid was determined and the pressure and force variations during the liquid removal were measured. In addition, the effects of the gas velocity, initial liquid amount, and gas flow ramp-up on the air-water flow phenomena were documented. Results of 3D and 2D numerical simulations (using OpenFOAM) were verified against the experimental data. The effects of employing different RANS turbulence models on the predictions were tested and demonstrated. A simple mechanistic model was established to predict the pressure and force variation during liquid displacement. The model enables inspecting the variation with the operational conditions of each pressure component (i.e., hydrostatic, friction, and acceleration) and examining their significance and contribution to the pressure rise.