IOGP Well Control Incident Lesson Sharing
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Several Well Control Incidents whilst drilling a sensitive section on MPD mode

IOGP Well Control Incident Lesson Sharing #24-5

This alert gathers several influxes experienced during a sensitive section drilled on Managed Pressure Drilling (MPD) mode. This illustrates how challenging it can be to maintain a surface back pressure and therefore the primary barrier system when you drill through a losses zone a typical loss & gain experience. It also shares how a simple error - a typo from the operator entering a wrong reference pressure in the MPD system can lead to a significant kick, emphasizing the importance of MPD operating system protections.

The Wells Expert Committee/Well Control Incident Subcommittee believes that this incident description contains sufficient lessons to be shared with the industry. We further encourage the recipients of this mail to share it further within their organization.

What happened?:

Drilling 8 1/2 phase in MPD mode, at 6959 m, observed a significant drilling break flow checked well, stable. Resumed drilling to 6962 m and observed losses. While trying to adjust the surface back pressure to control losses, trend suddenly changed to gain therefore increased surface back pressure to control flow out.

At the same time, experienced issues on mud pump suction, affecting SPP and the MPD mode.

Decision was taken to shut the well in on UAP.

Losses cumulative 66bbls Gain cumulative 72bbls. Attempted to initiate circulation, no return - influx was managed by bullheading same back to formation. No issue, well monitored stable.

Drilling was resumed but shortly some new instabilities of the well were again detected well was shut in on 2 other occasions, and subsequent influxes were resolved by another bullheading operation.

Note - Human error: 3rd influx was found to be caused by operator entering a wrong pressure value to maintain in the system (1250psi was entered instead of 12500psi) leading to a sudden opening of the choke and a loss of MPD Surface Back Pressure --> 6 bbls of gain entered the well.

Drilling of the section will be continued on a PMCD mode.

What Went Wrong?:

Faults crossed in the open hole jeopardized the mud weight window and the stability of the well.

Human error: 3rd influx was found to be caused by operator typing a wrong setting into the system leading to a sudden loss of MPD Surface Back Pressure and causing the full opening of the MPD choke.

Corrective Actions and Recommendations:

Raise level of vigilance when entering new setting into MPD system.

Modification of MPD system: it doesn't allow to enter a value below hydrostatic press + friction press (in case of human error).

safety alert number: 367
IOGP Well Control Incident Lesson Sharing


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