Measuring Gas and Liquid Phases in Oil & Gas Production

I’ll freely admit my bias toward fascination with the offshore oil & gas industry where my career began back in the mid 1980s. The technology has advanced quite a long way from those days. One area in particular is in measurement. It’s challenging to measure the oil & gas content from producing wells when the composition of oil, gas, water, and particulates coming up from the reservoir constantly changes.

Emerson’s Lars Anders Ruden, a member of the Roxar team, wrote an article, Do multiphase meters meet today’s offshore challenges?, for Offshore magazine. He described the advancement of these multiphase meters to measure liquid flow rates, gas flow rates, and the water liquid ratio (WLR). These meters must be able to withstand hydrogen sulfide from sour wells and be able to measure high-viscosity, heavy oils found in many offshore production fields.

These multiphase meters, initially based on microwave technology, came onto the scene in the early 1990s. Lars Anders noted that they:

…operated on a single velocity basis. This assumed homogenous flow and that liquid and gas were travelling at the same speed – clearly an assumption that operators cannot make today.

The next generation of meters could measure both liquid and gas velocity:

…the Roxar meter incorporated a Dual Velocity method with calculated phase fractions based on capacitance and conductivity measurements in combination with a single energy gamma densitometer, cross-correlation, and venturi section.

Lars Anders explained how this improvement helped with the velocity differences in the gas and liquid phases but required a fairly homogeneous flow pattern. Production wells can have complex, asymmetrical flow patterns with imperfect mixtures.

The latest generation of multiphase meters can address these complex flow patterns coming up from the reservoir. Lars Anders described how this technology:

…is based on an electrode geometry sensor which allows for measurements in separate sectors, as well as the full cross-section. This gives more combinations and more accurate fraction measurements and velocities for each segment.

A clearer picture emerges of the composition of the production stream and a more:

…accurate understanding of flow regimes, mixing effects and velocity profiles, and is able to detect rapid changes.

Multiple oil and gas flow velocities can be measured – velocities that will also vary over time, due to composition, turbulence, and viscosity.

The technology has advanced from microwave to electrical impedance tomography (EIT)–the technology used in medical imaging. That’s quite a versatile technology–from brain scans to multiphase hydrocarbon flow!

If you’re in an engineer in the oil & gas industry with responsibilities in production optimization, flow assurance, and well testing, I hope you’ll find the article to be worth your time to read.

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