Determining Atmospheric Pressure from UWI

In the previous blog post we went through a couple examples outlining the importance of having the correct atmospheric pressure entered into an Electronic Flow Meter’s configuration. So how do we go about determining the correct atmospheric pressure at a given location?

Some EFMs have built in capability to determine atmospheric pressure based on elevation. Assuming the technician on location had access to a GPS it would stand to reason they could determine their current elevation and rely on the flow computer to do the rest. This works well enough, but what if the technician doesn’t have access to a GPS, or what if the flow computer is incapable of calculating atmospheric pressure based off of elevation?
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Effects of Incorrect Atmospheric Pressure Correction

The AGA 3 and 8 Calculations reference atmospheric pressure. So does Directive 017 and API 21.1. But how exactly does it effect to gas measurement? If you refer back to your high school chemistry you will recall that base pressure is defined as 101.325 kPa. This is also the atmospheric pressure at sea level. When we refer to a volume of gas, it is always assumed to be at base conditions. (101.325 kPa and 15° C).  As you move above or below sea level atmospheric pressure decreases or increases accordingly. Because most pressure sensors are not installed at sea level, we need to correct accordingly to ensure that a given volume is gas is always that volume, regardless of what the atmospheric conditions are.

 So what effect does an incorrect atmospheric pressure correction have on gas volume? This post will outline two examples to illustrate the ramifications of an incorrect meter configuration. Read more