Emerson Process Management
The Multiphase Meter Market Today
There is no doubt that the market for multiphase meters within the oil and gas industry is continuing to grow.
Douglas Westwood, for example, predicts that there will be one thousand additional subsea multiphase meters deployed by 2015 and many operators are continuing the rapid deployment of such meters – both subsea and topside. Examples include Petrobras, who have indicated that they would like to see a multiphase meter on each of their subsea wells and trees; and Statoil, one of the first users of the technology, which today has more than 150 multiphase and wet gas meters in operation.
Multiphase meters are today a vital component of operators’ development and field production plans.
They can be used for production monitoring, individual well testing, production allocation and reservoir monitoring and they provide the operator with critical information on a well’s capabilities – information such as water saturation and break through, gas coning, permeability and flow characteristics.
Yet, there is plenty more room for growth. According to Rystad Energy Global, just 12% of global oil & gas production is currently facilitated by multiphase meters.
From 1st to 3rd Generation
In order to understand the current adoption of multiphase meters and their future potential, it is necessary to examine how they have developed. Multiphase meters have undergone a significant evolution since they first came on the market in the early 1990’s. The first commercial Roxar topside multiphase meter, for example, (launched in 1992) was based on microwave technology, operated on a single velocity basis, and assumed that homogenous flow and liquid and gas were travelling at the same speed.
In the early 2000’s, the second generation multiphase meters came to market (figure 1 shows a subsea version of the Roxar second generation meter). The meter allowed, for the first time, measurement of both liquid and gas velocities. The meter incorporated a Dual Velocity™ method with calculated phase fractions based on capacitance and conductivity measurements. The meter also came in combination with a single energy gamma densitometer and venturi section.
Other highlights of the second generation meter included parts designed to withstand more than 30 years of operating in harsh environments, power consumption at less than four times that of the first generation meter, and for subsea meters, a retrievable canister.
By this stage, the benefits to the operator were also clear. This included no separation requirements; no need for costly test separators; the instantaneous and continuous measurement of three phase rates – not just at a discrete point in time and not just for one well; and limited maintenance requirements. The result was substantial CAPEX/OPEX savings, increased well control, and enhanced production from the fields.
Changing Operator Needs
However, as multiphase meters continue to increase their market penetration, so do the challenges increase. Many oil & gas fields, for example, are more geologically complex, remote and heterogeneous than ever before. There is an even greater need for multiphase meters to generate accurate and reliable, real-time data from the wells to help diagnose and optimize the well’s performance and fend off flow assurance threats.
Such a need can’t necessarily be met by the second generation multiphase meter’s measurement principle which provides a simplification of complex flow patterns and is dependent on the reservoir being relatively homogeneous.
Secondly, the last few years have seen a growth in smaller fields (on average 200 to 300 million bbl) as well as brownfields. Only recently, Statoil announced that it is to focus further on brownfields to sustain production on the Norwegian Continental Shelf (NCS) at current levels.
Multiphase meters have an important role to play in brownfield developments in improving well testing in environments characterized by often complex interdependencies between aging and new technologies. There is also a subsequent need for an even simpler and compact meter design, which helps widen the operating envelope, increase flexibility, and lower the cost per meter.
Finally, there is the need to meet environmental and HSE requirements, particularly where the use of nucleonic sources is unacceptable, due to legislation or company policy. The ability for operators to forgo the nucleonic source within multiphase meters without forgoing accuracy remains a continuing challenge.
In summary, while second generation meters continue to be successful and effective, there is an increased onus on multiphase meters for even greater accuracy and a measurement principle that enables the operator to better handle complex, flow regimes and achieve maximum production rates.
There is also a need for multiphase meters to take on board environmental implications, widen the operating envelope, and operate at lower costs and in previously inaccessible locations.
The Third Generation Multiphase Meter
So how can the third generation multiphase meter (see figure 2) address these challenges?
The development of a new electrode geometry sensor for the meter, for example, can allow for measurements in separate sectors in addition to the full cross sectional area. This results in more combinations and more accurate fraction measurements and velocities for each segment.
Rather than being able to perform cross sectional measurements, the new measurement principle will allow the meter to perform both rotational near wall measurements and cross-volume measurements, thereby providing a comprehensive mapping of the flow regimes. Asymmetrical flow and less-than-perfect mixtures of the gas and dispersed phase can also be handled in a manner that was impossible with previous meters. The measurement principle is shown below in figures 3a and 3b (red indicates high sensitivity, blue indicates low sensitivity).
In this way, the operator can benefit from an accurate understanding of flow regimes, mixing effects and velocity profiles, and can detect rapid changes in compositon, thereby making the measurements more accurate and consistent than with other available technology.
There is also the potential for widening the operating envelope with the next generation of multiphase meters. This can be achieved through reduced height and weight, opening up substantial potential cost savings in terms of installation, maintenance and deck space.
Field Replaceable Insert Venturis also allow for extended service life and operating range, and can remove uncertainties in sizing meters based on uncertain production forecasts.
A meter with several Field Replaceable Insert Venturi sizes, for example, means that the optimal size can be selected for early life and replaced later with a different size in late production life. In this way, optimal performance from the venturi can be achieved.
Finally, there is the challenge of alleviating environmental concerns. To counteract concerns over nucleonic sources, non-radioactive meters can today cover the full operating range 0 -100% watercut and 0 – 95% GVF (gas volume fraction).
However, for those operators who are concerned with the limitations over the maximum GVF range or the slightly higher uncertainty than the gamma version, developments are underway in Emerson’s case to develop a densitometer based on X-rays as an alternative to the nucleonic gauge.
The X-ray based densitometer, known as FluorX and developed in conjunction with PANalytica, utilizes attenuation measurements of the same photon energies as a low energy gamma-ray source, and provides the same measurement accuracy. Adding a FluorX system to the non-gamma meter version means that the meter can be used in the full 0-100% GVF range and also ensures improved accuracy, as our tests have shown.
Much More to Come!
With the market for multiphase meters continuing to grow and the need for accurate flow measurement and a wider operating envelope as important as ever, it is imperative that today’s multiphase meters are able to meet operator challenges.
A new measurement principle, new electrode geometry and near wall measurements are ensuring that multiphase meters continue to evolve to meet such demands.
Such technical developments, as well as meeting environmental concerns through developments, such as the x-ray based densitometer, will ensure that multiphase metering becomes ever more prevalent – not just in well testing but in reservoir monitoring, flow assurance calculations, and production optimization.
Vincent Vieugue is Vice President of Sales & Marketing at Roxar Flow Measurement, part of Emerson Process Management.