Lessons Learned: Influx, Drilling Cemented Shoe Track
Influx while drilling cemented shoe track.
An influx occurred while drilling out the liner shoe track. The influx was caused by the combination of a failure of the liner cement job to fully isolate a sand formation and a reduction in mud weight for the next hole section creating underbalance. It is likely that a high-density PAD (pump-and-dump) mud pill, spotted on bottom prior to running the liner, was not effectively displaced as part of the cement job and, as a consequence, led to channeling in the cement.
An influx while drilling a cemented shoe track would not normally be identified as a risk. On this occasion the crew was vigilant, the volume was small, and the influx was safely removed from the well.
What happened?
While drilling the shoe track inside a 9.7/8″ liner at 20363 ft MD (23 ft above guide shoe) after reducing the mud weight from 11.7 ppg to 11.1 ppg for the next hole section an increase in background gas to 2656 units was observed. A flow check on the trip tank observed a 1.5 barrel gain and the well was shut in. The well was killed using conventional techniques increasing the mud weight to 11.7 ppg. Investigation identified sand in the previous hole section was in pressure communication with the casing.
What went wrong?
The plan was to leave high density pad mud in the open hole rat hole below the liner shoe. Excess pad mud was left in the casing annulus and most likely created a channel on the low side of the wellbore and the sand did not have cement isolation.
Cement displacement modeling determined that the high-density pad mud would not be displaced from the low side creating the channel for pressure communication to the shoe.
Corrective actions and recommendations
Circulate out the excess high density pad mud with the drilling bottom hole assembly before pulling out of the hole to run casing.
Content source/credit: IOGP (International Oil & Gas Producers), Well Control Incident Lesson Sharing, 25-9, “Influx while drilling cemented shoe track.”
