October 2017, Vol. 244, No. 10
TechNotes
Midstream Company Solves Flow Measurement Issues
When Mike Heckl was a director of operations for Crestwood Midstream, the company established itself in the West Virginia Appalachian Basin by purchasing an area of development from a major upstream firm with a large acreage in the Ohio and West Virginia Marcellus/Utica Shale fields. They had already installed about 45 miles of pipe at this location with several dozen well pads flowing natural gas. They were not a midstream company, so Crestwood purchased the right to transport the gas for that particular area.
Limited Measurement Available
The upstream company had built this pipeline knowing it would be sold to a midstream operator. It contained few extra features as the operator’s biggest concern was moving the gas to a compressor station where it could be processed, compressed, and moved down the line. The only flow measurement system available was at the well pad and at the inlet of the compressor stations.
So Heckl had a pipeline with no intermediate measurement and was unable to tell which direction the gas was flowing. And when water mixed with the gas, it caused a back pressure buildup. So he had to rely on those two measurements but was unable to verify that the system was in balance. As they were paid at the well pad, they had a plus/minus 1% that they could absorb. If it was outside of that balancing realm, they would have to absorb the additional cost.
Nor was that all. Heckl had a crew that pigged the pipeline to remove water.
If the gas was flowing in one direction and the crew wanted to pig in the opposite direction, they would be unable to. There was no telling which way the gas was flowing. So the crew would put a pig in the pig launcher and it wouldn’t leave.
New Metering Too Costly
There were two locations where Heckl knew that the pressure buildup was, but he couldn’t determine which direction the gas was flowing and where the water was building up. Wherever he had a riser or a valve setting, there was an opportunity to do a measurement. However, they couldn’t afford to shut down a pipeline, cut into it, blow it down, weld flanges on and install meters. What was needed was an external meter that would provide the accurate measurement necessary to determine flow direction and to identify water buildup.
An Ultrasonic Solution
Heckl contacted Rich Oberst, a sales engineer for M.S. Jacobs, a rep firm in West Virginia. After visiting the site Oberst recommended a tool that would not disrupt pipeline operation and provide 1-2% flow accuracy. The tool was an ultrasonic clamp-on meter from FLEXIM Americas. It is clamped on the exterior of the pipe, providing the required measurements, even bi-directional.
How Ultrasonic Flow Metering Works
“The technique most ultrasonic flow meters use is called ‘transit-time difference’. It exploits the fact that the transmission speed of an ultrasonic signal depends on the flow velocity of the carrier medium, like a swimmer swimming against the current,” said Izzy Rivera, gas product manager for FLEXIM Americas.
“The signal moves slower against the flow than with it. Transit-time inline meters have become the industry standard for custody transfer measurement. Clamp-on meters are becoming the secondary standard of measurement where 1% accuracy is acceptable,” he added.
Heckl said he preferred some portable over permanently installed meters because they would be constantly moved so they could take targeted flow measurements.
Water in the Mix
“I never used the ultrasonic meters to measure water on the actual pipeline itself, however it was possible to see there was water by using the meter’s signal diagnostics that indicate turbulence, signal strength, and signal variation. When the signal strength drops and signal variation increases, it’s an indicator of water content. We could also rotate the transducers to the top of the pipe to help gauge how much water we had.”
The project eventually utilized four ultrasonic meters. Two were kept stationary to function as crossroads for the gas. The others were moved around, using them as check meters, and meters for the compressor station. The meters helped Heckl’s team redesign and set up the inlet facilities to enable them to get all of the sand, water, and oil out of the natural gas. It also gave them needed check measurement.
Heckl took his experience with ultrasonics to an Appalachian Gas Measurement short course which was attended by his peers. He suggested they not just look solely at ultrasonic meters as a measurement source, but also as a functioning tool.
“My bottom line was that for a modest investment of about $25,000 I attained check measurement that helped me to balance my system and improve our profit margin by locating and correcting our losses. By having these ultrasonic portable meters provide check measurement, I found areas that were giving me problems so I could isolate sections, saving me a lot of work and time.
“The same meter goes on an 8-, 12-, 16-, and 20-inch pipeline. Even on short runs where I didn’t have the required upstream and downstream length of pipe, the meters were still giving me 2% accuracy,” Heckl said.
Jack Sine is a freelance writer specializing in HVAC, flow measurement, green buildings, and IAQ issues. He can be reached at jack.sine@verizon.net or at 845-831-6578.
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