Question about Wellhead Casing

[polo.gaputan]

Hi,

I have a question about measuring fugitive methane emissions from abandoned or "orphan" oil and gas wells.

ACR (American Carbon Registry) published a methodology encompassing measuring fugitive emissions by connecting to the wellhead casing. I was wondering if this would be representative of fugitive methane emissions (leaks due to improper plugging of the well). From my understanding, the wellhead casing is not directly connected to the production tubing and any gas from the casing is due to any leaks from the tubing and the casings.

Here is a link to the methodology: https://acrcarbon.org/methodology/plugging-orphaned-oil-and-gas-wells/

Thanks for the help in advance.

 

[1503-44]

The production tubing is usually removed before the well is plugged forever.
If the well casing is not properly plugged, the gas from the gas bearing strata makes it's way around the plug into the upper region of the casing. It is that gas in the casing that can leak to the atmosphere.

 

[polo.gaputan]

The production tubing is usually removed before the well is plugged forever.
If the well casing is not properly plugged, the gas from the gas bearing strata makes it's way around the plug into the upper region of the casing. It is that gas in the casing that can leak to the atmosphere.

This helps a lot, so that mean's if you are hooking up a flow meter to the tap of the casing, you are effectively overestimating the amount of gas that would leak since it's a direct connection to the gas in the casing, right vs. the gas slowly leaking over time from small openings?

 

[1503-44]

Yes. Flow through a valve would not represent gas leaking from the casing.

I am not familiar with casing leak monitoring devices, however from the emission monitoring methodology you referenced, I imagine more of a box or tent set up enclosing a known space around the well head in which they monitor the gas inside (in terms of ppm) that accumulates over time.
There should be no direct flow from the casing through a valve into that space, which would have no relation to a flow via any other route.