Well flow testing using Expro PassiveSonar

This is a story from the October issue of the Industrial Automation INSIDER, that would not fit onto the small format mobile friendly version of the newsletter, so it is shown here for readers to be able to access it from their mobile devices. Obviously no-one whose company has not paid their subscription to the INSIDER newsletter should read the following text!

Expro specialize in well flow management services and products. A subsidiary, Expro Meters, based in Wallingford, Connecticut, supply clamp-on ultrasonic flow m e a s u r e m e n t techniques that parallel the technology used in the phased passive sonar arrays used by submarines: these are called, simply, PassiveSonar. These meters were first introduced in 2003, following an exclusive deal with the developers of the technology – CiDRA, also of Wallingford (a Teknoinvest of Norway company) – and they are used to enable oil and gas producers to realize increased value from their wells and fields through improved production monitoring, for optimization of well performance, increased efficiency and reduced metering costs.

At Offshore Europe last month, in collaboration with Marathon Oil in the UK, staff from Expro presented a paper describing the use of PassiveSonar on the East Brae platform, where there are currently 12 producing gas wells. Varying water-gas ratios and low gas rates result in liquid loading being a major flow assurance issue. Well testing is carried out every two months using the Expro clamp-on flow meters – because they are clamp-on units there is no interruption to the production flows while the meter is installed. Different methods have been adopted to optimize production and combat liquid loading: wireless wellhead temperature sensors recently installed have been correlated with sonar measured gas rates, providing a real time trend of liquid loading.

How do they measure?

PassiveSonar is well suited for high liquid loading multiphase flows typical of black oil wells and low pressure gas wells. The flow measurement principle relies on the natural turbulence and noise of the flow producing a pattern that is detectable by the passive sensors, which is time shifted as it travels down the pipe. So I would describe it as a cross-correlation technique.

The same units are quoted to measure the entrained gas percentage, or gas void fraction, 0 to 20%, determined by a measurement of the sound speed through the process medium. In the East Brae example the flow is mainly water, with some gas entrainment, so the principle would be valid, but how the speed of sound can be measured passively does not seem immediately obvious!

There are 1500 Expro PassiveSonar meters quoted as installed world-wide.

Another style of clamp-on flowmeter is the ActiveSonar meter, launched in 2009, which is best suited for gas and gas condensate wells flowing in heavy schedule pipes. It uses a clamp-on array of ultrasonic transmitters opposite the receiver array.

Krohne Australia leverage

In Australia, Krohne have been applying the CiDRA Sonar technology to difficult applications outside the oil and gas sector – primarily in the minerals and mining industry – for several years: earlier this year they signed an agreement with CiDRA to sell these products across the whole of Asia and Australasia.

Following this, Krohne have now signed an agreement with Expro, who have the exclusive rights to oil and gas applications, to resell the Expro versions of these systems for upstream and midstream oil and gas applications throughout Asia and Australia, alongside the standard Krohne portfolio of flow metering systems – which includes conventional ultrasonic meters for both gas and liquids, including LNG and oil.

Patrick Matthews, md of Krohne Australia, said: “The sales agreement with Expro is a strategic partnership of high importance for Krohne in Asia and the Pacific. We also believe this relationship will enhance our position to establish a centre of excellence for reservoir management and wet gas metering in Asia”. Craig Watterson, global sales manager at Expro Meters, commented “The Krohne Asia organization has technical knowledge of and years of experience with PassiveSonar metering technology. This combination makes them a uniquely qualified strategic reseller for us in Asia”.