Most operators don’t like playing Santa Claus with their gas production (ie “giving away” gas to your purchaser…)
The Savvy Operator realizes that almost anything that happens to the meter run equipment will result in gas going unmeasured. That’s why GreaseBook has compiled a short two-part series on gas production.
Most gas sales contracts stipulate that no adjustments to the gas measurement device are required as long as the device maintains an accuracy of 2%. Heck, even if a problem is identified, most contracts state that the purchaser will only go back half-way to last time the measurement was known to be correct.
Unfortunately, the cards are stacked against the producer in the game of gas sales.The purchaser of the gas almost never loses, that’s why it’s so important to treat your gas measurement equipment with the care it deserves.
Although orifice metering equipment claims an accuracy level somewhere in the neighborhood of ¼% to ½%, take note that this level of accuracy is only achievable when equipment is in “like new” condition and is installed and compliant according to ANSI/API 2530 standards (ie the American National Standards Institute).
The orifice plate is a producer’s friend. The orifice plate helps us to form the vena contrata, which enables us to accurately measure the differential pressure across the plate. When we experience a decrease in differential pressure, the vena contrata gets wider which means less gas flow. When there’s an increase in differential pressure, the opposite happens and our vena contrata gets smaller signifying more gas flow.
All technical jargon aside, the orifice plate does a remarkable job when properly cared for. However, any variations, nicks, corrosion, warping, or scratches on the orifice plate will result in skewed measurements. In fact, any variation of the orifice will cause an enlarged vena contrata which means less measured gas production!
Tip 1: When not using your orifice plates, a small amount of grease should be applied on both sides and the plates should be stored flat. Never hang your orifice plates on a wire or hook.
Tip 2: Orifice plates should only be purchased from manufacturers that can meet the required specs. What are those specs you may ask? The orifice’s plate must be correct within 5/10,000ths per inch of diameter, and the surface of the plate should not exceed 50 micro inches. But, consumer beware! There are few machine shops that can accomplish this kind of precision.
Check out some of the statistics of mishandled orifice plates presented during one of the Oklahoma Marginal Well Commission pumper workshops:
- A plate bent toward the gas flow ⅛ inch will result in a loss of 2.8% of gas to the seller.
- A coating of grease 1/16 inches thick on both sides of the plate results in the seller losing more than 15% of the gas
- If the upstream edge of the orifice plate is beveled just 0.01 inches, 2% is “given away”
What does the Savvy Operator do? He knows that the best insurance is to have a expert present when a sales meter is installed and calibrated at one of his leases. This professional should be equipped with an extremely accurate set of mircometers, and be familiar with ANSI/API 2530.
To further minimize total gas “given away”, be sure your sales meter is checked and calibrated monthly, and that it’s opened up for internal inspection once a year.
Stay tuned for Part 2!