Wrong practices for influx detection while manipulating fluids at the surface

While drilling the 8 ½" section, an 8m³ drilling fluid transfer to the active pit was carried out from the reserve pit which was not equipped with sensors. At this point, a sudden increase of SPP and mud flow-out percentage were detected, and bubbling was observed from the rig floor. The well was shut in, showing the following data: SICP stabilized at 2700 psi, SIDPP at 75 psi (float valve present in the BHA) and an approximated gain of 15 m³.

The well was controlled implementing the driller's method with a final MW of 2.24 (after four cycles of mud increments).

What Went Wrong?:

• The pit volume was masked by the ongoing drilling fluid transferring operation at the surface. The total gas influx was estimated between 10-20 m³
• The pore pressure estimated for well design (1.78 sg) was significantly lower than the pore pressure encountered (estimated at 2.18 sg)
• People's awareness of the associated risks proved to be low; gas had been circulated while drilling, but it was not associated with the fluids' transfer risk
• Detection systems did not work as intended: The theoretical threshold for detection was 5 bbls, but the system allowed an influx >10m³

Corrective Actions and Recommendations:

• Implement a program to increase awareness of well integrity operations and associated risks
• Review and enhance influx detection system
• Define clear instructions for fluid transferring at the surface to avoid losing control of the active system
• Implement detection drills for well influx to reduce closing time. Reinforce procedural adherence both for the supervisory staff and the crew

safety alert number: 322
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