Commingled multiphase flows – the metering challenge
Gary Miller - TUV NEL
Metering and allocation of the oil and gas industry is more complicated than ever. Production flows are no longer straightforward. Instead, various streams made up of differing mixes of oil, water, and gas from different fields belonging to different operators and sometimes even under different tax regimes, are being commingled as an increasing number of marginal fields enter production.
A new approach to metering is required and “per-well” multiphase meters appear to be the best way. But, is the technology ready? Meter manufacturers believe so, but TUV NEL, which has performed independent testing of multiphase meters over the past 20 years, believes more testing and verification is required to give field operators the confidence and experience to meet their commitment to partners and regulatory bodies.
Most offshore fields developed 20 or 30 years ago were designed to cope with flow from a single field. While it always has been important to monitor individual well production, it generally has not been essential to know which well every single barrel of oil came from when it all belonged to one operator. However, when you add the complexities of multiple flows belonging to different operators, each with varying oil/water/gas mixes, things become much more complex.
The traditional approach to offshore multiphase flow metering has been to use a test separator and separate oil and gas flowmeters, with periodic testing of flows from each well. This is adequate to provide regular information about what each well is producing in terms of oil, water, and gas, but in terms of allocation, when every drop of oil counts, its suitability and applicability is questioned.
On a typical platform with 10 - 20 producing wells feeding into a single production separator, changes to a specific well’s production could remain unnoticed for weeks, even months, until the well flow takes its turn in the test separator. As more established offshore assets become production hubs for multiple fields, any undetected changes to flow rates, water, and gas content can have cost implications. For example, a sudden water breakthrough in a well which previously produced several thousand barrels per day could reduce revenues for all of the stakeholders and fiscal bodies, as well as financially affecting the operator of the facility.
What is really required is continuous, individual “per well” flow metering. Separation systems are costly, large, and heavy. It is not practical in terms of deck space or cost to have individual separation for each well, so multiphase metering has to be the way forward. However, uncertainty remains about the application, suitability, and performance of multiphase meters.
Multiphase metering – is it ready?
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Volume 68 Issue 9
September 2008
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