Wax deposition simulation for North-Sea pipeline An integrated approach

摘要

The potential of wax deposition has been evaluated for a major sub sea pipeline system, that is used to evacuate gas/condensate produced from gas fields located in the Dutch sector of the North-Sea. An integrated approach has been used where pipeline flow simulations, thermodynamic Solid-Liquid-Vapour (SLV) cakubtions and wax deposition simulations have been combined. This approach allowed prediction of wax formation under different operating conditions. The study reported here used actual gas and condensate samples representative for the fluids being produced. Special attention has been given to the sample taking process. The study clearly identified those sections of the pipeline prone to wax deposition. We also found retrograde condensation in the trunk line to drastically diminish the potential of wax deposition. Retrograde condensation depends on gas composition, and the pipe line pressure and temperature conditions. Therefore, flow and thermodynamic modelling with a comprehensive set of PVT data has been used to predict condensate drop-out in the various pipeline sections. Conversely, adding "lean" gas to the system will increase wax deposition potential. The study concluded that under present producing conditions no significant wax deposition was to be expected. This was field validated by carrying out a scraper run in the wax prone section of the pipeline system. We acknowledge the contributions of: N.S. Seunsom, P.M. O'Neal, N.M. Utech and J.F. Nimmons at Shell Global Solutions and P.R.G. van der Thiel at Nederlanse Aardolie Maatschappij.