Measuring onshore gas with SICK’s FLOWSIC600 ultrasonic gas flow meter

Gas well
applications need tough equipment

On the
coast of Holland, gas reservoirs are pumped out down to the last cubic centimetre. Shell commissioned the construction
of a mobile measurement station, KISS, designed especially to measure this
remaining amount. The station makes it possible to approach wells and set up
equipment for them flexibly, in line with
application requirements, using a portable metering skid. The station’s
successor – KISS next – has now arrived, bringing improvements and new features,
enabled by the use of the FLOWSIC600 ultrasonic gas flow meter from SICK for
stable gas volume measurement.

The gas
is pumped up from 5,000 metres below the surface at the onshore deposits
and then either used internally by Shell or sold to customers directly from the
well. As a result, it is crucial that the gas flow is measured extremely
accurately, even in the event of widely fluctuating pressures. No one wants to
pay too much – and these are no small sums. A lot is demanded from quantity measurement at the well due to the
variable properties of the gas.

The
quality of the untreated gas varies in its composition depending on deposits –
for one thing, it is wet because it contains water and condensate. Sand and dirt
are also transported to the surface, contaminating the gas. The temperatures
fluctuate between ‚Äí20 and +115 ¡C; temperature drifts must, therefore, be
ruled out during measurement. When it comes to measuring gas, the bar has been set high, which creates challenges and
imposes conditions – on the measuring device, on the technology, and on
installation and maintenance. The project is not just attractive for Shell, one
of the largest oil and natural gas companies in the world; it is also important
to meet the Dutch government’s energy
policy as well as gas producers worldwide.

Dutch natural gas

In the Netherlands,
natural gas is a key source of energy and accounts for nearly half of the total
energy mix. As we enter a new era regarding
energy, an intelligent approach to gas production is crucial. Even small gas
fields can support the Dutch government’s energy policy.

“Economical production is a fundamental
requirement for this. This includes lowering costs, using new technologies, and
taking advantage of infrastructure,” explains Ying Tang, Metering Engineer at
Shell in conversation with Jšrg Wenzel, Head of
Product Marketing Services at SICK.

Keep it simple and
smart – is that what KISS from Shell refers to?

Exactly, that’s KISS
– a compact and mobile gas system, approximately 12m long, 2m wide, and 2m
high, for small gas fields. SICK launched KISS in 2004. In doing so, the goal
was achieved: to design an innovative type of technology for extracting natural
gas in small fields – in a simple, standardised,
and automated manner, with reduced production, commissioning and project costs.
If a well dries up, KISS is loaded onto the truck and transported to another
well. The practical construction and installation also simplify the entire
process, from planning right through to delivery. Positioned on the well, KISS has plug-and-play functionality,
meaning it can be connected to control centres
quickly and directly. The gas flow is controlled,
and the pressure and temperature are monitored from there.

The gas quantity
must be recorded in a reliable and accurate manner, which means that the right
technology plays a key role. When did Shell decide to use ultrasonic gas flow
meters from SICK?

At the point when
KISS next came about. When you’ve
launched something new on the market, you want to keep perfecting it. Optimising the gas flow measurement was crucial as the gas flow meter is one of the
main components in KISS next. The differential pressure measurement used
previously with Venturi was too restrictive when it came to the flow range. As
a result, different designs were required,
and this often resulted in conversion
work – while also having to cope with fluctuating flows. In the end, the
installation conditions meant that the overall design of Venturi was too large
and costly. We had to find a feasible solution to fit for purpose. That is now
the FLOWSIC600.

Does the
FLOWSIC600 fulfil the legal requirements
for measuring devices and measuring conditions?

In
addition to the main characteristics it offers, the measuring device needs to
cover a wide range of applications and reduce the skid size significantly. We
spoke to a few manufacturers so that we could gage the application requirements
for the meter performance in good time. We discussed minimum inlet zones, the measuring
properties of the untreated and wet gas,
changing conditions in the process, noises in lines, and – most importantly – the very high level of
measurement accuracy. That’s something we have to be able to depend on. We were impressed with the ultrasonic gas flow meter from SICK. The ultrasonic
technology from SICK demonstrated clear advantages over the previous Venturi
flow measurement principle.

Can you
give examples of some of the advantages?

The direct path
layout of the FLOWSIC600 is much more rugged in wet and dirty gas mixtures.
Reflection paths, for example, quickly fail because
dirt influences the reflection. What’s more, the FLOWSIC600 has a much wider
measuring range of 1:120, complies with the volume fraction of more than 1
percent (LVF < 1%) for wet gas measurement, and also has a longer service
life. Just what we need – and we can ensure fault-free operation.

What does ensuring
fault-free operation mean to Shell?

The technology that we use needs to be
reliable. We expect gas flow meters to measure very accurately for the long
term. Even the noise from the pressure regulator, which is installed directly
opposite the gas flow meter and makes a lot of noise, does not affect the FLOWSIC600. However, if the
measurement is affected, we need to know the cause as soon as possible. Only
then can we respond quickly and initiate countermeasures. With the MEPAFLOW CBM software solution from SICK, we
get user-friendly data access to the FLOWSIC600 with lots of diagnostic
options, such as the ability to check the signal-to-noise ratio or gain
parameters. If these change, this could indicate contamination or an increase
in CO2. Any impairments, which arise are displayed before they have an impact on the measurement. This is ideal for us – when
it comes down to it, we want to ensure high extraction volumes without faults
and delays so that we can affirm Shell’s excellent reputation as a reliable
supplier.

So everything is
flowing smoothly – even when it comes to the legal requirements?

Of course. The
FLOWSIC600 has all the relevant certificates for explosion protection. On top
of this, it has to fulfil the
requirements of ISO 17089 for ultrasonic flow measurement. In the standards and
at Shell, measuring tasks with different accuracy requirements are categorised in
different classes. At Shell, there are three classes: Class 1 is provided for custody transfer gas
measurement involving large quantities of gas, and
the uncertainty must be less than 1 percent. Class 2 is also for sales and
taxation, but between facilities and entities with less than 2 percent
uncertainty. Class 3 is typically used
for the gas production area close to the well with a maximum measurement
uncertainty of 10 percent.

With the FLOWSIC600,
we achieve class 2, despite the liquid content in the gas. As a result, we can use the skids in an even more versatile manner. Local
authorities can also remove one path (path 4) to achieve Class 2 requirement, as
the FLOWSIC600 is certified with its four
MID measuring paths.

How long has a
mobile measurement station of this kind been in operation? And do you also sell
KISS to other oil companies?

KISS has been designed with a service life of 25 years.
All skids are ready for delivery on demand from the warehouse – KISS, KISS
next, or Chemical Injection skids. We have currently built 5 of the 12 planned
KISS next units. With KISS next, the system design is
even slimmer and more cost-efficient, and mobility has become even more
convenient. The standardised
high-level pre-production means that it can be constructed on site within one to two weeks. At the moment, we
are only aware of a few relocations of complete skids. However, this will soon
change when companies start processing their fields one after the other. With
the FLOWSIC600 gas flow meters, it is even possible to serve a group of wells
with the same skid.

Shell
and SICK have set precedents – can we expect success from them
?

The
mobile gas system is already one of the most remarkable system developments.
Without this innovative development, a lot of natural gas would probably remain unused underground. The KISS skid is
small but refined – it regulates the gas flow in small natural gas fields, and controls and
monitors the flow, pressure, and temperature. The outstanding system technology goes hand in
hand with low investment and operating costs – that’s remarkable in itself.
With the rugged and compact FLOWSIC600 ultrasonic gas flow meter, we can cover
an enormous flow range reliably, the system monitors itself constantly and
provides intelligent device diagnostics, and we get a measurement with
long-term stability.

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