Dynamic Simulation for Optimising Pigging Frequency for Dewaxing

Abstract

Abstract The presence of paraffin in crude oil often leads to wax deposition in pipelines when temperatures reach below Wax appearance temperatures. It is possible to simulate the wax build up using thermodynamic and kinetic/deposition models for estimating wax deposition with varied degree of accuracy. The most popular remediation technique for wax removal is direct mechanical cleaning using pigs as these are generally cheaper than chemical inhibitors. The pigging frequency is mostly determined using thumb rules and operating experience. Correct pigging frequency is essential to avoid significant wax build-up in pipeline that may lead to plugging or stuck pig. This becomes more acute in subsea lines where insufficient well head pressures driving the pig may not scrap out the wax plug ahead of pig. This can increase to downtime and can lead to expensive pipeline repair. In Mumbai offshore pigging is most common method of wax removal in well fluid lines. In this paper a simulation model using dynamic simulator for predicting daily wax build-up and pigging shall be discussed. The model is based on the actual pipeline condition, fluid parameters and pigging data. Extensive lab studies on actual comingled well fluid samples from platform have been carried out for capturing the Fluid & Wax properties. The model has been used to run what if scenarios by varying the pigging frequency for the pipelines. The impact of ambient temperature or increase in gas (lift gas) in well fluid on pigging has been studied. Sensitivity studies have been carried out for various parameters like wax plug friction, bypass opening, change in well fluid parameters, etc.