It’s great to see situations where an industry regulatory group updates standards to take advantage of new technologies. API has done this recently, and the result is better field custody transfer procedures for crude oil from lease tanks, with improved accuracy and worker safety.
With the growth of unconventional oil production, the number of smaller fields where crude oil needs to be picked up by truck has expanded, but for a long time API was still enforcing techniques and procedures from nearly 30 years ago. Fortunately, in 2016 the group updated its standard. How this affects producers is the topic of my article in the October issue of Oil & Gas Engineering, API 18.2 Recommendations Improve Level Instrumentation. Some producers are still coming to grips with how this has changed and how their practices can take advantage of the new possibilities.
Prior to 2016, the methods for measuring and evaluating oil during custody transfer from a wellhead site were described in API MPMS, Chapter 18.1: Measurement Procedures for Crude Oil Gathered from Lease Tanks by Truck. This standard was published in 1990 and became widely recognized as the accepted method for this type of custody transfer. API MPMS, Chapter 18.1 was updated over the years before being supplanted in 2016 by API MPMS, Chapter 18.2: Custody Transfer of Crude Oil from Lease Tanks Using Alternative Measurement Methods, which is now the recognized standard and offers significant advances over its predecessor.
The advancements are truly significant and the article goes into more detail. The largest advance relates to how the oil level is measured. The old look-in-the-hatch-with-flashlight-and-tape-measure technique can now be replaced with a far safer and more accurate approach.
The truck driver climbs to the top of the tank, opens a thief hatch and lowers a tape measure with a float to determine the oil level. This first measurement is called the opening gauge and establishes the baseline measurement. When the transfer is over, the driver takes a second level measurement (closing gauge) with the tape to calculate the volume transferred based on the tank’s dimensions.
You see the point. Accuracy depends entirely on the driver’s skill and fastidiousness, which means it can be off by a couple percent. It’s also quite dangerous because the driver doesn’t know what fumes may have accumulated in the tank. Opening the hatch could release a plume of H2S, and personnel have been killed in exactly those circumstances.
There is no specific number on how many drivers were greeted by an unwelcome blast of hydrocarbon fumes or toxic hydrogen sulfide expelled from the tank. The fortunate ones probably only suffered dizziness, fainting, headaches or nausea. Others weren’t so lucky. Between 2010 and 2014 the National Institute for Occupational Safety and Health identified nine fatalities of workers overcome during manual tank gauging and sampling operations. This heart-breaking fact was one of the key drivers in the development of API MPMS, Chapter 18.2.
Arguably the most practical tank level measuring technology for this application is guided-wave radar (GWR) and Emerson has a family of products. GWR has a higher degree of accuracy and is far more consistent than manual methods. It can also measure the amount of water that may have accumulated under the oil. Two leading product candidates are Emerson’s Rosemount 5300 Level Transmitter and Rosemount 3308 Wireless Level Transmitter.
Using a GWR level gauge along with temperature transmitters and other electronic instrumentation provides the ability to tie readings directly to a data-gathering platform, greatly reducing the potential for errors. Additionally, the use of GWR for level measurement, instead of float-based technologies, can improve measurement reliability and help to monitor separation.
You can find more information like this and meet with other people looking at the same kinds of situations in the Emerson Exchange365 community. It’s a place where you can communicate and exchange information with experts and peers in all sorts of industries around the world. Look for the Level Group and other specialty areas for suggestions and answers.
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