Multiphase flowmeasurements

In multiphase flow measurements, the challenge is to measure a mixture of gases and liquids. This is the case with the exploration of oil wells. Besides oil, also gas and water come to the surface. A multiphase flow meter (MPFM) is used to measure the flow rate of this oil-gas-water mixture.

Why is flow measured directly on an oil well?

When oil wells are explored, gas and water almost always come to the surface as well. This has to do with the strata in which the oil is found. If the well is drilled too deep, water will come up and if the well is drilled too high, gas will be pumped up. The proportion of water and gas gives oil companies information with which they can manage the exploitation of the well. On a drilling platform, the water and gas are separated from the oil by so-called seperators. But directly at the well, one wants to measure the water-oil-gas ratio. This is called multhiphase wellhead flow measurement.

Different types of multiphase flowmeters

In the past decades, several designs of multiphase flowmeters have been developed. Sometimes such a flow meter resembles a separator in which the various phases are first separated, then measured individually, and then reassembled. Other instruments use different techniques, including density measurements using nuclear radiation, although these are used less and less. Which version is most suitable usually depends on the application. Multiphase flowmeters are becoming increasingly compact and there are also versions suitable for subsea installation.

Venturi differential pressure flowmeters for wellheads

Separating the phases before measuring them separately has a number of disadvantages, including the complexity of this type of flowmeter. This is why there are nowadays also wellhead flowmeters in models that are based on a vertically installed venturi differential pressure flowmeter. Double sensors are installed in the venturi to measure the conductivity and capacity of the medium. The oil-gas-water mixture first passes the lower ring of sensors and then the upper ring. The two measurement signals, which contain variations, are compared by means of autocorrelation techniques, after which the speed of the mixture is determined.

Surprisingly, the venturi is not intended for the flow measurement, but to calculate the density of the mixture. In some cases, this avoids the need to use radioactive sources.