Negative Planning LL with DNO

Oselvar (A-3 HT2) – P&A

What happened:

Total planned well volume was 150 m3 (tubing 50 m3, annulus 100 m3). After pumping 81 m3 the rig header box H2S alarm tripped in the CCR (10 ppm warning value, 20 ppm trip value). Pumping was stopped and the well closed in.
A new plan and DOP was developed to resume reverse circulation through the Schlumberger bleed-off package. Before pumping all surface pits were pre-treated with H2S scavenger. The bleed-off package MEG injection pump was also used to inject scavenger into the returns. Returns were taken to the bleed-off package and SoilTech treatment tank with an H2S detector hanging from a rope. Flowrate was matched to the flowrate that SoilTech could manage – could not risk taking returns to the mud pits where an H2S alarm could trigger a rig ESD.

What was planned:

Reverse circulate the well to 1.35 SG brine using rig pumps and flushing reel taking returns through KWV to rig choke manifold. Plan was to divert returns to Schlumberger bleed-off package if hydrocarbons were detected.

What was learned:

H2S could be generated in an old well. Any alarm due to 20 ppm has the same consequence. Best to prepare to inject / treat circulating system with scavenger to minimise risk of an alarm.

What actions are required:

Plan on pretreating all pits prior to displacement with H2S scavenger.
Plan on treating returns at choke manifold with scavenger.
Investigate possibility of injecting scavenger at SSTT.
Plan on 24 hour cover for bleed-off package (2 per shift, 4 total) during reverse circulation.