An experimental study on air-water surge waves is conducted in the multiphase flow laboratory at NTNU. A special configuration of a 57 meter long test pipeline of 60 mm I.D. was prepared with 3 pipes and two bends. The waves were generated in a dip in the pipe close to the inlet after a variation of the gas flowrate. The wave propagation behavior along the pipeline was recorded with conductance ring proves. The wave characteristics were compared with OLGA simulations with good results.
Surge waves are mainly a transient phenomenon that is initiated by a change from one steady state to another. In gas-condensate pipelines the surge waves can be initiated by a change in the production rate. The oscillations in the liquid flow are caused by liquid mass waves propagating down the pipeline with a velocity close to the liquid transport velocity [1]. Surge waves normally occur during production at low flow rates, typically during production ramp up [2] and sometimes also during ramp down [3]. When the production rate is increased the pipeline will move from a state with a large liquid content to a state with less liquid content. When this excess liquid is expelled out of the pipeline, it is seen as a long surge wave at the outlet [2]. The liquid content (condensed fluids and inhibitors) in the pipelines is normally very low. A surge wave is a modest surface elevation with a very long wavelength, and the waves can potentially flood the receiving facilities. Validation of dynamic flow simulators for the prediction of surge waves occurrence and behaviour is then of high importance.
It has been a challenge for commercial transient multiphase flow simulators to predict surge waves in gas-condensate systems satisfactorily [1]. With special tuning of their models, FlowManager could give excellent prediction of surge waves observed in the Ormen Lange field [4]. There are still uncertainties for other fields or systems, in particular regarding three phase flows. The main reasons are weak understandings of the basic fluid mechanics in the initiation of surge waves, and the dynamics of the wave propagation.
In the current work, an experimental study is conducted to investigate the possibility of reproducing surge waves in a small scale laboratory with air and water at atmospheric pressure. The experimental data can then be used for comparisons with dynamic flow simulators.
