Until recently multiphase flow meters have been at an Infant stage of development Only a handful of meters have been field tested, and then only in a limited amount of onshore / offshore locations and applications However, papers on the Subject of subsea multiphase metering has previously been presented at various venues, this has been described elsewhere, Ref 121, but no subsea multiphase flow meter has yet been field tested
However, the successful application of the KOS Multiphase Flow meter (MCF) in onshore installations have led to an increased interest in applying these meters also for subsea developments The potential for cost reductions resulting from reduced capital expenditure as well as reduced operational cost are substantial The added complexity resulting from marinization of a technology which has yet to be fully field proven and accepted, poses great challenges Challenges such as, space limitations, installation method (permanent or insert), location (flow prediction), reliability and availability, power and signal transfer, maintenance, intervention, and last but not least - operational requirements and expectations
This is illustrated with relevant examples of design solutions for the MCF, which is now being prepared for subsea applications
Kongsberg Offshore a s (KOS) in cooperation with Shell Research and A/S Norske Shell, has completed the first two stages of development for a surface multiphase flowmeter, named the Multi Component Flowmeter (MCF) A number of these meters have been tested m the laboratory, as well as m onshore field installations, with very good results The test results has been described elsewhere, Ref /4/ Some of these meters are now permanently installed in the field, where they are being used for continuous well monitoring and surveillance, as well as for reservoir management
During multiphase flow the distribution of liquids and gas across and along the pipe are not homogeneous, but vanes with time even when the flowrates for liquid and gas are fixed The variation in distribution increase considerably with changing flowrates, and various distinct flow regimes occurs Flow regimes are also dependant on the piping installation i e vertical or horizontal, flowrates, obstructions etc
Multiphase pipe flow is thus classified m different flow regimes, as described in the "Mandane Flow Map" for multiphase flow in horizontal pipes, Refer Figure 1. The type of flow regime occurring in a pipe is also dependent on operating conditions, fluid properties, pipe inclination and upstream/downstream conditions
Flow conditions at the various locations can be dramatically different Some wells are "clean" oil producers with little water, sand, wax etc Others are more complex with surging gas production and / or surging watercuts Others again have high sand production, and some have problems with waxy crude
In addition the flow patterns in the multiphase flow lines can vary One minute being a well mixed fluid, the next a slugging flow Some wells being natural producers, others being dependant on gas lift or engineered pressure maintenance (gas / water injection) for flowing
