Shell's mobile gas measurement system for small fields

Shell’s mobile measurement station, known as KISS, makes it possible to approach wells and set up equipment for them flexibly, in line with the application requirements, using a portable metering skid. The station’s successor — KISS next — has now arrived, bringing improvements and new features.

The gas is pumped up from 5000 m 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.

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 -20 and +115°C — temperature drifts must therefore be compensated for.

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,” explained Ying Tang, metering engineer at Shell.

KISS is a compact and mobile gas system for small gas fields, approximately 12 m long, 2 m wide and 2 m high. In launching KISS in 2004, the goal was 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 a 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.

Optimising the gas flow measurement was crucial as the gas flow meter is one of the main components. The differential pressure measurement used previously with Venturi technology 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. For KISS next it was necessary to find a feasible solution to fit for purpose, which turned out to be the FLOWSIC600 from SICK.

“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,” said Ying Tang. “We spoke to a few manufacturers so that we could gauge the application requirements for the meter performance.

“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.

“It turned out that the ultrasonic technology from SICK demonstrated clear advantages over the previous Venturi flow measurement principle.”

The direct path layout of the FLOWSIC600 is 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% (LVF <1%) for wet gas measurement and also has a longer service life.

“The technology that we use needs to be reliable,” said Ying Tang. “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,” he continued. “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.”

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%. Class 2 is also for sales and taxation, but between facilities and entities with less than 2%. Class 3 is typically used for the gas production area close to the well with a maximum measurement uncertainty of 10%.

The FLOWSIC600 enabled Shell to achieve Class 2, despite the liquid content in the gas. As a result, the company 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.

“KISS has been designed with a service life of 25 years,” said Ying Tang. “All skids are ready for delivery on demand from the warehouse — KISS, KISS next or Shell’s chemical injection skids.

“With KISS next, the system design is even slimmer and more cost-efficient, and mobility has become even more convenient. The standardised high-level preproduction 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.”