The use of sphering for liquid management is widely employed on gas condensate export pipelines. Field data for routine ‘undersized’ sphering operations of a 20" gas condensate pipeline was analysed, and OLGA (v2015.1.1 & v2017.1.0) simulations set up to try and match the displaced surge volumes. The results show that OLGA is unable to accurately predict both the total liquid and aqueous phase volumes when the actual sphere diameter is used, but this is improved when the sphere is modelled as larger than reality. Adjusting the leakage factor ‘through’ the sphere does not affect the predicted surge volumes.
The Breagh platform in the Southern North Sea has been exporting gas condensate to the Teeside Gas Processing Plant (TGPP) for the last 5 years via an approximately 110 km, 20" wet gas pipeline. The pipeline is currently operating below its minimum sweep velocity, at flowrates of approximately 100 MMscfd, resulting in liquid accumulation in the pipeline greater than the onshore separator capacity. Because of this lower flowrate, the pipeline is routinely sphered for liquid management to ensure the pipeline liquid inventory remains below the onshore slug catcher capacity of 4000 bbls of liquid.