A new three phase flowmeter

A fascinating technology development now released by Krohne is a new approach to oil, gas and water multi-phase flow measurement. Actually launched last November, maybe because everyone said “What?” the Krohne Academy guys have now come up with an on-line e-learning course – to introduce their M-Phase 5000 Nuclear Magnetic Resonance flowmeter. The name refers to the technology, not to anything remotely nasty like nuclear sources, X-rays or radioactive isotopes – there is nothing like that. In fact there is nothing untoward in the flow tube at all, it is a straight tube with an unobstructed bore, available in sizes from 4 inches down to 2 inches, with an operating turndown of 60:1.

Krohne M5000 2

I first met Nuclear Magnetic Resonance (NMR) when fresh out of University, but had not heard of it even then: it was used to make a Magnetometer, to measure the Earth’s magnetic field. Basically you wrap a coil round a bottle of water, to create a strong magnetic field, which lines up all the spins of the hydrogen atoms (the protons). The coil current is then interrupted, and as the protons try to realign themselves with the Earth’s ambient magnetic field, they precess round the direction of this field at a frequency determined by the strength of the field. The weak rotating AC magnetic field from this precession can be measured by a detector coil.

How it works

The NMR principle was discovered in the early 1900s, and as the Krohne introduction says, two Nobel prizes were awarded for research into the topic in 2003, in relation to the soft tissue medical imaging techniques used in MRI (Magnetic Resonance Imaging) scanners. Krohne have worked on developing the technique for three phase flow measurement for 10 years, in co-operation with Shell Research and NAM of Rotterdam, a joint Shell/Exxon company. For the last four years this has involved field trials of the first versions, both in labs and in test installations.



The final flowmeter can be seen on tinyurl.com/Ptalk-NMR, a 90 second video from Krohne. Horizontally mounted, the meter is about 12 feet long, and contains a glass-reinforced epoxy flow tube within a stainless housing. The first section has three separate magnetising zones, which can be driven separately, and this has the only moving part of the whole meter, a motor to arrange the different modes (this is outside the flow tube). Then the next section is the area where RF pulses are applied to the 3-phase fluid, which can be across the whole pipe or can interrogate horizontal layers across the pipe. This section also has the detectors, which measure the magnetic field transmitted by the protons at the ‘Larmor’ precession frequency, and the amplitude and decay of these signals following various different imposed magnetic field patterns. These different measurements (frequency, amplitude and decay rate) enable the computation of the flow of each of the three phases. Any sand or gravel flow is recorded as gas. At the exit of the flowmeter a separate tapping allows pressure and temperature to be monitored, which is the further data normally required in well test and production allocation applications.

The technique has been previously described in detail at the North Sea Flow Measurement Workshops, for example in 2013.

Operating parameters

The meter uses around 180 Watts of power, but is approved for installation in Zone 1 areas, with all the electronics and power/data connections in flameproof boxes. The fluid temperature can be up to 93°C, and the pressure should be 8 bar minimum for gas measurement duty, 224 bar max. There are no special installation pipe bend restrictions. The flow range is typically 2.5 to 150 m³/hr, and measurement accuracy 3-5% of measured value, after the meter has been set up on site to establish the characteristics of the oil being monitored, using a full pipe static test. The at-line conditions data output can be fed to a flow computer to give totalisation of all three phases, and PVT conversion to refer volumes back to standard conditions.

The Krohne M-Phase 5000 is launched and available for production well metering now, and the Krohne Academy training course is even giving out certificates to confirm you understand the meter operation, once you have done the e-learning training course! Find it on www.academy-online.krohne.com – I passed the test, and have a certificate!

© Nick Denbow, Processingtalk.info



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