Multiphase Meters and Their Application in Wet Gas Fields, Offshore Brazil
Authors: Tol Martijn Pieter , Brandt Morten , Kristensen Geir 
Published: October 2011

With the increase in offshore, deepwater wet gas fields - defined as gas condensate reservoirs with around 90%-100% gas void fraction [GVF] - the accurate measurement of small amounts of water is critical for detecting water breakthrough and for flow assurance. This is particular the case, offshore Brasil.

Against this context, this paper will look at the development of a third generation multiphase meter (based on field impedance electronics, a 2–6 dual plane electrode geometry, and a field replaceable insert venturi) and how it has been further developed and tested to perform with a high degree of accuracy in wet gas fields with a GVF of up to 100%.

The paper will look at the wet gas flow tests for the wet gas version of the meter which took place at the Colorado Experiment Engineering Station Inc. (CEESI) and will demonstrate how the impedance sensor geometry and electronics generate accurate and stable permittivity measurements in wet gas flow for water volume fraction, as well as gas condensate measurements.

The paper will also explain how these results were used to develop a more accurate wet gas model which allowed for dynamic water measurements that is not dependant on Water Cut (WC) input. It will also look at how the mechanical design of the meter allows the changing out of the venturi, so that the venturi beta ratio can be adapted to the actual mass flow rate, without replacing the complete meter. The result is significant savings for the operator and the continuation of highly accurate dP measurements.

The paper will conclude by demonstrating that electrical impedance measurements, in combination with venturi-based flow measurements and high energy gamma density measurements, cover the complete range between 0–100% GVF. It will also highlight the flexibility of the meter and how a compact and simply designed multiphase/wet gas flow meter can be designed without the moving of intrusive parts and with a very low danger of leak paths, with significant applications for wet gas fields, offshore Brasil.

Introduction - The Multiphase and Wet Gas Meter Market Today and their Applications in Wet Gas Fields

The Multiphase- and Wet Gas Meter Market

The last few years have seen considerable growth in multiphase and wet gas meters across the world and particularly in offshore Brasil. Such meters have important applications in well testing, reservoir monitoring, production monitoring, production allocation and flow assurance.

Douglas Westwood, in its 2006 Subsea Processing Gamechanger Report, estimates that expenditure on subsea processing systems is expected to climb to US$3.4 billion over the 2006-2015 period, with one thousand additional subsea multiphase meters likely to be deployed. A recent article in Oil & Gas Journal by Gioia Falcone of Texas A&M University and Bob Harrison from Soluzioni Idrocarburi Srl found the authors estimating that, as of 2010, there were 3,314 multiphase meters and wet gas meters installed worldwide, with this number potentially doubling over the next 10 years.