INVESTIGATION OF WAX DEPOSITION DEVELOPMENT IN SARIR-TOBRUK PIPELINE

Abstract

Wax deposition in pipelines is one of the biggest flow assurance challenges in the oil industry. The 
need for understanding deposition becomes greater as hydrocarbons are being transported over increasingly 
greater distances. Transportation of waxy crude oil in a cold environment can result in wax depositions on the 
pipe wall. The problem of wax deposition seriously adversely affects the normal operation of a pipeline that 
might lead to a complete shutdown in some cases and imposes considerable loses in production. This study 
takes a look at the wax deposition phenomena which has been experienced recently in the onshore SarirTobruk pipeline. The pipeline carries an average of 200,000 barrel per day from Sarir Field to the Al-Hariga 
Port at Tobruk (514km). The study aims to understand the behavior and mechanism of wax deposition in the 
pipeline and how it is influenced by the operational parameters. Software HYSYS was used to examine the 
effects of inlet operation conditions including inlet crude oil temperature and flow rate and environmental 
conditions (ambient temperature) on wax deposition development in the pipeline. It also aims to investigate 
the energy requirement for heating the crude before it is pumped into the pipeline in both winter and summer 
seasons. Important results of wax deposition have been reported from the simulation. Increasing of inlet crude 
oil temperature and time duration cause increases of wax thickness layer. However, increases of ambient 
temperature causes decreasing of wax thickness layer. The temperature effect of both inlet crude oil and 
ambient indicates that wax deposition development is predominantly thermally driven. Also, investigation of 
energy requirement shows that 130ºF is suitable inlet operation temperature, especially in the winter season 
to avoid any jelly formation phenomena for the crude oil before reaching its destination at Al-Hariga Port. 
The effect of flow rate showed that increasing of flow rate causes an increase in the wax thickness layer. This 
result relates to the fact that models based on molecular diffusion do not account for the shear forces where 
the effects of shear removal start to act. It is recommended to conduct further studies incorporating other 
methods and compare with real operating data once the pipeline is taken for maintenance or renewing; wax 
thickness measurements become possible and the real wax profile can be obtained.