A Flow Assurance System (FAS) is installed on Ormen Lange 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:
Virtual Flow Metering System (VFMS):
Model calculated values of flow rates as backup to physical multiphase meters.
Pipeline Monitoring System (PMS):
Model calculated values of pipeline flowing conditions and onshore receiving facilities.
Leakage and Blockage Detection (LDS):
Combining information from measurements and model calculated values of pressures and flow rates along with statistical process control methods.
In 2011 the FAS was upgraded with the transient multiphase flow simulator FlowManager™ Dynamic, replacing the previous simulator. In this paper, it is shown that the new simulator gives accurate model predictions, which is essential for all the modules in the FAS.
The flow assurance challenges of the Ormen Lange field are significant. Due to sub-zero temperatures at the sea bed, there is a risk of hydrate and ice formation. However, the FAS reduces the risk of hydrate and ice formation. The transient simulator calculates pressure, temperature, water content and MEG concentration through the entire subsea system, giving the margin to the hydrate formation curve for actual operation conditions.
Another flow assurance 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 this paper it is shown that the new transient simulator is able to accurately predict the liquid surges including arrival time and liquid level in the slug catchers. Thus, the operators and flow assurance engineers have a tool to optimize the ramp-up speed avoiding flooding of the slug catchers.
The FAS gives full overview of current operation conditions and predicted changes in the subsea system and slug catchers the next 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.