WOOD Group Kenny’s virtual metering systems (VMS) came to the fore roughly 20 years ago as the company moved to find new ways of monitoring subsea flow rates, but today the technology has new challenges to face and new fields to discover.
WGK’s regional manager for Australia James Holbeach told Oil & Gas Australia the systems are today deployed on about 1,000 wells for about 10 different operators across the world, in some cases complementing existing physical meters and in others replacing them entirely.
“Probably most of our installations over the last few years have been in response to some high failure rates of the physical meters – and this is an insurance policy, so if the physical meter fails, you have a back-up,” Dr Holbeach said.
“Every single well will already have instrumentation on it … so that will be things like downhole pressure, top hole pressure on both sides of the production choke, temperature instruments etc.
“All our system does is take those data points and uses a set of methods and algorithms to determine what the likely flow rate is based on those measurements,” he said.
Dr Holbeach told Oil & Gas Australia that VMS technology had had its origins in the North Sea, as WGK needed to find a new way of metering flow and predicting flow in a closed loop production system.
“We had to develop a method by which we could calculate what the flow rate was just based on the pressures and the temperature data that we had available,” he said.
Five years later, the company was asked to develop a standalone metering service.
“The operator in that case needed to know the well flow rates for hydrate and corrosion inhibition calculations,” he said.
“Traditional subsea metering for them was a bit cost prohibitive, and there was some concern that they wouldn’t last long enough, so the operator decided to install some redundant well instrumentation instead and install a virtual metering solution for that project.”
The WGK VMS system uses seven different methods to determine flow rates – each using a different set of data points. This allows for double checking and, in some cases, removal of the uncertainty surrounding some methods.
“Our systems use not just the hydraulic pressure drop, but we also use the temperature drop in the system, and that can often be a very good indicator of what the likely water flow rate is from the well,” Dr Holbeach said.
“We can add in other sensor data, for example if you have any other sensor data that measures the flow or the properties of the fluid or potentially the composition etc., that kind of information can be fed in and can increase the accuracy into the future.”
This large number of sources can also see a VMS used as a method of well surveillance – with the variations in data enabling experts to pinpoint an area where either corrosion, a potential fouling or wax deposition may have occurred.
“If you don’t have that constant, real time well surveillance through that virtual medium you might not know that,” Dr Holbeach said.
“You wouldn’t if the flow rates are varying quite a lot, which tends to happen, and that is one thing that a virtual meter will give you that a physical meter can’t, because it is just measuring one location whereas virtual meters measure across the entire system, or at least to the choke.”
While VMS technology had originally been designed for conventional targets at subsea and offshore facilities, Dr Holbeach said the company had also applied it to onshore conventional wells.
WGK had also developed a VMS system suitable for unconventional projects, he said, adding that there were new challenges to face in this sector.
Existing subsea VMSs needed to deal with much higher flowrates and throughput than would be present on a coal seam gas well, which typically produced much less gas than conventional wells.
“A single (coal seam gas) well may produce one hundredth of what an offshore conventional well may produce, so therefore a light version of the VMS for coal (seam gas) is required to make the price right for the marketplace,” Dr Holbeach said.
The company has since developed such a solution, with Dr Holbeach saying WGK was looking seriously at developing solutions to suit potential future clients. The group had recently set up offices in Brisbane.
Dr Holbeach is set to discuss the various uses of VMS technologies and the various forms they can take at the Australasian Oil & Gas Exhibition & Conference.
Speaking at the Subsea Controls, Sensors & Monitoring session, he will look at how issues such as sensor loss, poor fluid specification and rapidly changing environments have been dealt with in practice.
The event will be held in Perth from 11 to 13 March, 2015.