More than Just PTA… Checking differentials provides added value. Note this case where an unusual reversal was exhibited by the tubing/casing differential after flowing the well. This suggested there may have been an air column trapped in the annulus. Subsequent review of completion reports revealed that the well had, indeed, been blown dry with air before installing coiled tubing! An air/methane mixture is volatile and could have proven catastrophic during tie-in or start-up operations. The author knows of one compressor being blown up due to a similar situation!