More than 80% crude oils produced in China has a high content of wax. Pipeline transportation for such high waxy Chinese crude has a serious safety risk due to its characteristics of high gel point (up to 30 degree) and high viscosity below the wax appearance temperature. In the case of pipeline shutdown the crude cools down. After a certain amount of time, depending on the crude oil properties, the crude oil temperature plot file, the hydraulic data as well as the pipeline construction and environmental related data, the required pressure to restart the pipeline might exceed the maximum allowable operation pressure (MAOP) which makes the restart of operation become very difficult or even impossible.
To mitigate the safety risk in case of the pipeline shutdown or to avoid congeal accident, determining the safe time after which the pipeline is still able to restart is necessary. However, the complexity of the presented problem lies in the uncertainty of the operation parameters and the environmental related data, such as the uncertainly of the flow rate and natural temperature.
A method is developed to predict the safe time based on the uncertainty of parameters. In the method, the field data is firstly collected, then processed and analyzed to obtain the static rules of these data. By doing so, the complexity of uncertainty is successfully handled. The method is then applied to two pipelines, the results show that the safety of the pipeline is ensured and the energy consumption is also significantly reduced.
