The Vestprosess pipeline carries NGL from Kollsnes by Sture to Mongstad, all located on the west coast of Norway. The boundary conditions of a pipeline are important for optimization and future operation of the pipeline. History has shown NGL pump capacity challenges in the Vestprosess system. For this reason technical and commercial aspects that could influence the boundary conditions were studied by different projects. The scope of work in the current study was to perform detailed thermo-hydraulic simulations of the pipeline, capacity evaluations, and quality check input to and results from ongoing studies by the owners. The overall purpose of the study was to combine all results and understandings from previous and current studies in order to increase operational robustness of the Vestprosess pipeline.
The study of pipeline capacity and optimization of a pipeline network require detailed thermo-hydraulic simulations. Two key elements for a hydraulic pipeline simulation are quality checked input data and the possibility to match the model to real measurements. In addition to the pipeline itself it is important to understand the boundary conditions and the processing facilities connected to the pipeline. Changes in the operating conditions of a pipeline may affect and influence the operation of the processing facilities. In 2009 the Vestprosess pipeline was undergoing several separate studies initiated by the owners. The purpose of the studies was to optimize the pipeline based on their understanding of the existing boundaries. During this work one of the options was to invest millions of USD in two new condensate pumps to meet future transportation estimates. This would have been a significant investment, and the owners were therefore interested in further analysis of the Vestprosess system. The current study was therefore initiated to ensure that all aspects were covered in terms of capacity optimizations. The different options for upgrading the capacity in Vestprosess were:
Kollsens: Potensial upgrade of the condensate pumps and use of drag reducer
Mongstad: Solution to improve flexibility at high rate scenario at Mongstad
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Indirect feed to cavern (evaluation of pressure loss from cavern to process)
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Change of diameter (8" to 12") for the pipeline going from cavern to process
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General: Variation in rate scenario in Vestprosess from Sture and Kollsnes
The capacity study was carried out using different simulation tools. The main simulation tools were the OLGA Transient Multiphase Flow Simulator (v.5.3.2), GAP multiphase oil and gas optimiser tool and basic flow equations for pressure drop. PVT-sim (v.18) was used for fluid characterization of the OLGA PVT input file. The simulation tools were matched against pipeline measurements to ensure that the models were satisfactory.
The Vestprosess pipeline connects the following three processing facilities: Kollsnes processing plant treats gas from the Troll, Kvitebjørn and Visund fields in the North Sea. NGL (63° API) is separated from the rich gas, and the remaining dry gas is pressurised before being transported to customers in Europe. NGL from Kollsnes may be stabilized or partly stabilized, depending on the process conditions at Kollsnes.
