Deep Gas Leak in Annulus A

DAS provides novel key data for well integrity decision making and compliance

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Abnormal pressures in annuli A and C in a North Sea oil producer. 


  • Visually tracked deep gas leaking up the annulus A  and ruled out risky inter-annuli communication
  • Quantified gas rising speed and gas leak rate
  • Identified liquid-gas interface in annulus A
  • Established DFO as a valuable and better data source to support well integrity compliance


  • Establish the probable leak paths in annulus A and C
  • Rule out inter-annuli communication
  • Find the liquid level in annulus A
  • Validate a source of better well integrity data


The Z-System sensing rod was run into the well down to the depth of interest and remained parked there during the entire acquisition continuously sensing the entire wellbore length from the bottom of the rod to surface. Firstly both DTS and DAS shut-in baselines were recorded followed by a bleed-off and build-up sequence of annulus C then A. Then the well was produced and eventually shut-in again. Though the temperature profiles don’t show any leak signature, the DAS processed data show spectacular evidence that the leak in annulus A brings deep gas to surface but stays confined to annulus A. Other leak detection techniques are unable to provide visual and dynamic event tracking, missing out on key data to make compliance decisions.
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