Just a FYI; Generally chromatographs on rigs (Mudlogging Units) measure hydrocarbons, not CO2. That's a CO2 detector, If the unit had one. Pre MWD/LWD (c. early 1980's)all gas was measured by chromatographs at surface by mudloggers and lagged back to depth. In addition, background, trip,cxn gas etc was taken our of the total gas to get 'drilled TG'. The chromatograph broke down the TG into C1 C2 C3 etc. Gas ratios (Howarth etal)were used to check the 'signature' of the gas from each zone. And if the well is drilled on or over balance (Mud weight =/+ than formation pressure) then gasses should not mingle in the wellbore. All this is basic wellsite practice - mudlogging and wellsite geology. And then to the Ops Geo in town to QC this stuff. It can be done and should be done. It costs nothing and doesn't fail often. It used to be done. Poor operations from the Geological POV.
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