An Innovative Solution for Any Wet Gas and Multiphase Flowmeters with in situ Flow Validation
Authors: Pinguet Bruno 
Published: September 2022

Accurately measuring oil, water, and gas flow rates is a significant difficulty for the oil and gas sector. Multiphase flow meters or wet gas flow meters (i.e. MPFM) have opened the door to the development of marginal assets and promote more efficient production of a large field with continuous monitoring. However, this MPFM must be calibrated, and a correct uncertainty assessment is necessary, particularly for the allocation method. The new paradigm is to calibrate them in the field, as well as to achieve in situ validation, to significantly cut OPEX. Indeed, MPFM's manufacturers frequently charge a monthly fee to ensure the technology's performance over time without being able to independently assert the MPFM's performance, leaving the end-user to conduct their tests to determine the MPFM's true field performance.

How do we address the in situ of MFPM performance?

There are two methods. The first is to take the manufacturer's statement, literature, and the laboratory's knowledge to establish the performance at line conditions, to ensure that the estimations are accurate. Monte Carlo simulation analysis is a way to do it. It is possible to define the key parameters to monitor to determine whether the MPFM is still in a healthy condition and within the sweet range. But in this extremely conventional and conservative business, this strategy is sometimes viewed as too much data computational driven and not as strong as the second method which is to do an MPFM performance review at the well site, either by a remote witnessing or a physical third party service.

This process is typically done if there are any uncertainties about the MPFM's performance but requires supplementary equipment to verify it. Third-party experts are frequently consulted at an early stage to advise on what might be required as the best metering solution to define and use as a reference, bearing in mind that space, timing, and measurement principles must be simple to comprehend to establish or confirm the performance of the so-called reference flowmeter.

Our research has established that reported MPFM performance is, on average, too optimistic, based on the manufacturer's claims only. It was demonstrated that manufacturers rarely disclose the predicted output specification (i.e. uncertainty) of oil, water, and gas flow rates to the end-user. Rather than that, they provide a mixture of various output parameters at line conditions. And to the lack of competencies in fluid behavior (i.e. PVT) necessary to convert flow rate to standard conditions, there is no way to establish a correct performance statement for the end-user.

This leaves the end-user to translate/calculate/convert any stated numbers to the expected parameters and associated values by themselves. Sometimes, the manufacturers have provided them with enough relevant data or information to achieve this. Finally, there are no standard requirements that can be applied directly because of the complexity and multiphase metering expertise is required to achieve such a statement.

In summary, to describe precisely the uncertainty and define the calibration frequency, and hence the performance of MPFMs, expertise and precise calculations are required. A thorough mapping of MPFM performance to its in situ application should be established by end-users or with the support of third-party multiphase flowmeter experts – and validated at a calibration facility when possible. Using a third party for a statement avoids buyer-seller conflict over who is right or wrong. For example, when you fill up your car's tank, you do not contest the reading from the pump because an NMI organization (i.e. NIST, NEL…) has stated and verified the true performance of the flowmeter (single phase in this case) used on your behalf, fostering a healthy business.