Prediction of liquid surge waves at Ormen Lange

摘要

A Flow Assurance System (FAS) is installed at the Ormen Lange field in order to give information about the multiphase flow through the entire subsea production and pipeline system and onshore slug catchers to support the operation of the field. The FAS includes the following modules: 1. Virtual Flow Metering System (VFMS): Model calculated values of flow rates (gas, condensate and water) as backup for physical multiphase meters. 2. Pipeline Monitoring System (PMS): Model calculated values of pipeline flowing conditions and onshore receiving facilities. 3. Leakage and Blockage Detection System (LDS): Combining information from measurements and model generated values of pressures and flow rates with Statistical Process Control (SPC) methods. In 2011 the Ormen Lange FAS was upgraded with new PMS and LDS modules based on the new transient multiphase flow simulator FlowManager™ Dynamic, replacing the previous transient simulator. The new simulator has proven to give accurate predictions of pressure, temperature and flow rates of gas, condensate and water/MEG in the wells, templates, flowlines and slug catchers. In this paper, it is shown that the new simulator gives accurate model predictions, which is essential for the modules in the FAS. The flow assurance challenges of the Ormen Lange field are significant. The main challenge is liquid surges. The long transport (120 km) of unprocessed fluids in a hilly seabed terrain induces liquid surges in the pipelines due to liquid accumulation at low rates. In the worst case, the result can be flooding of slug catchers. In this paper it is shown that the upgraded PMS module is able to accurately predict the liquid surges in the pipelines, liquid surge arrival in the slug catcher and the liquid level in the slug catchers. Thus, the operators and flow assurance engineers have a tool to optimize the ramp-up speed to avoid flooding of the slug catchers. The PMS module gives a full overview of current operation conditions and predicted changes in the subsea system and slug catchers for the next few hours. All operations (e.g. shut-in, restart or ramp-up) can be simulated in advance. This ensures safe and optimized operation of the complex Ormen Lange production systems.