DAVID W SPITZER'S E-ZINE (February 2026)

The process control objective is to maintain the desired mass concentration of each injection chemical at each strategic location in the well. Proprietary information can be used to determine the concentration for each chemical and location, from which individual chemical injection flow rates can be calculated and maintained during operation, subject to operator adjustment. The unmeasured production flow can vary significantly during operation. The control strategy of maintaining fixed chemical injection flow rates in conjunction with significant uncertainty surrounding the actual production mass flow rate can result in overfeeding or underfeeding chemicals, both having potentially significant effects on well operation.

For example, if the actual production mass flow is 10 percent higher than its assumed flow, the injection chemical concentrations at strategic locations will be approximately 10 percent lower than their desired amounts, adversely affecting the productivity of the well by a potentially large amount, while not adequately protecting the well and its equipment.

Excerpted from Measuring Difficult Flow Streams and More Accurate Flow Control Can Improve Oil and Gas Well Profitability in Processing magazine.

Investigation revealed that the actual line size was 16 inches. This change alone would increase the flow measurement by approximately (16/14) squared or 30 percent. A more rigorous calculation could be performed using the actual internal diameters of the pipes. However, this cursory result shows that only part of the incorrect measurement could be attributed to configuration of the incorrect pipe size.

This particular vortex shedding flowmeter has software that filters the signal that so as to process signals that are within a frequency band and amplitude band where the measurement would be expected to be located --- whereby other “signals” at other frequencies and/or amplitudes would be considered to be noise. In other words, the flowmeter attempts to lock onto the legitimate flow signal to achieve accurate measurement and reduce the effects of noise.

After some investigation, the vortex shedding flowmeter was found to be configured using the properties of water. Therefore, due to the large difference between the properties of water as compared to the actual liquid, the vortex shedding flowmeter was likely filtering in such a manner as to track a part of the signal that did not correspond to the actual flow measurement --- thereby causing flow measurement errors.

The configuration was changed to reflect the actual process liquid and the proper line size after which the vortex shedder measurement approximately agreed with the expected flow measurement.

Problem solved? Check in next month.

This article originally appeared in Flow Control magazine.

Differential pressure flowmeters such as averaging Pitot tubes can be used to measure stack flow and are often used for official stack testing. Thermal flowmeters and ultrasonic flowmeters have also been developed for stack flow measurements. Magnetic flowmeters are for liquids only and cannot be used in this application. Therefore, Answer B is the correct answer.

Additional Complicating Factors

Selecting the best stack gas flowmeter is dependent upon a number of factors to include the gas temperature, ambient temperature, flowmeter location, available straight run, amount of particulates in the gas, moisture content, and the chemical composition of the gas.

For example, high levels of particulate in the gas can cause the ports in a differential pressure flowmeter to plug, coat thermal sensors, and obstruct the beam in an ultrasonic flowmeter. High moisture content in conjunction with some particulates can similarly coat sensors and plug ports. Locating an averaging Pitot tube flow transmitter outdoors with exposure to sun, rain and snow can cause it to be difficult to calibrate and subject to drift as ambient conditions change from day-to-night and summer-to-winter. Single point stack flowmeters can be affected by poor velocity profile when sufficient straight run is not available.

In the end, flowmeter selection for this application is not as straightforward as it may appear.

This article originally appeared in Flow Control magazine.