Wet Gas Measurement. Oil & Gas Measurement Podcast. Episode 33. Eric Harman. 2024.
Guest
Eric Harman. Principal Engineer at Wet Gas Test Facility for the Colorado Engineering Experiment Station, Inc. (CEESI).and an expert in flow measurement, with over 40 years of experience specializing in gas, liquid, and multiphase measurement, particularly wet gas complexities.
Accuracy
People falsely assume that in the wet gas world, you can be within a percent or two. Typically, even the best wet gas meter, they’re lucky to be in the five to ten percent range. That is the world we live in and that’s what gas is all about.
Custody transfer measurement
Also called fiscal metering, defines the exact point where ownership or legal responsibility of natural gas changes hands between two independent parties, such as a producer and an operator, or a seller and a buyer. Drives direct financial invoices, taxation, and regulatory compliance. Requires extreme accuracy and low uncertainty, like ultrasonic or Coriolis flow meters paired with gas chromatographs for energy content.
Allocation measurement
Mathematical and metering process used to split or distribute a total, commingled volume of gas measured at a downstream main facility back to individual contributing sources, such as specific wells, platforms, or production fields. Used when gas from multiple owners or leases is mixed together into a shared pipeline before being sold. Assigns shares of total production, royalties, taxes, and transport costs back to each stakeholder. Tolerates a higher degree of individual measurement uncertainty because errors tend to net out across the total shared stream.
Multiphase flow
Simultaneous movement of two or more thermodynamic phases or components (such as gas, liquid, and solid) in a channel or pipe.
Orifice plate metersGas and liquid flowing down the pipe. The liquid tends to flow like a river along the bottom of the pipe. Imagine trying to measure fast moving gas coming down the pipe at the exact same time as that river that’s moving significantly slower with a greatly larger density, that can be as much as a factor of 800. That liquid will get picked up by the gas. It will start creating waves. It will start to become stratified. It will crawl up along the walls. There will be droplets and mists of liquid in the gas flow. It is just a jumbled mess.
With two differential pressures, responding to the liquid loading differently, you can actually improve your uncertainty by as much as two thirds. Let’s say you’re off by 30 percent, if you wet gas correct it, you can get within 10 percent, which is pretty good. Orifice plates are certainly a very viable option for wet gas measurement.
The new technology: Multipath ultrasonic meters
The lower path of an ultrasonic meter will be experiencing more liquid because the liquid likes to hang out on the bottom of the pipe. There’ll be less liquid on the upper paths. By measuring the velocity ratios, they’re really separate meters. For the first time we can see inside the pipe, at different elevations. It’s like a telescope, looking into a pipe.
Resistance to change.
“I just wanted to tell you about my technology.” said the salesman, “I’ll give you two minutes.” replied the vicepresident. He gave a spiel, and the executive said, “You know what? We use a different vendor, and we’re sticking with that vendor. Be on your way.” He turned around and started to walk off. The sales guy goes, “Well, you know what? It takes courage to change. Do you have courage?” He was walking away, and stopped dead in his tracks. He turned around and said, “I have courage. I’ll cut you an order. I’ll give you a shot.”
We don’t like to change. We keep doing things as we’ve always done. It seems like it takes decades for us to change. There’s a lot of technologies out there and we are very dogmatic. If we want to grow as an industry, we need to have courage to try new things, and in the long run, measurement will be better.
