MPD Software Input Results in WCI

IOGP Well Control Incident Lesson Sharing #23-7

During Managed Pressure Drilling (MPD) a software input resulted in the reduction of Surface Back Pressure (SBP) and consequently a kick. As no flow from the well was observed, a pump efficiency discrepancy was assumed and drilling proceeded. Although there are many causes for a loss of SBP that could contribute to a WCI, please consider what human factors contributed to this incident in your review.

The IOGP 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.

During 8 1/2" drilling phase, after measuring the SCR (slow circulation rate) pressure and while measuring the kill and choke line friction loss, because of a communication failure between the MPD team, the MPD operator did not change the previous pump selection on MPD Software (maintaining the selection of the SCR operation). This caused an influx of 10 bbl. The virtual trip tank showed consistent gain, but the operator and the supervisor assumed it was a divergence between the real pump efficiency and the MPD software input pump efficiency. No gain was observed on the active tank. Drilling began, and the kick was pumped partially above the BOP, without notice. Afterwards, the MPD supervisor discovered the wrong pump selection. The well was shut on the BOP, hydrocarbons below it were bullheaded, and above it was circulated through the MPD manifold, and then through the mud gas separator, with 520 UGT (Total Gas Unit) gas pick, without abnormalities.

What Went Wrong?:

1. Inadequate pump selection on MPD software and inadequate understanding of the consequences of this wrong selection by the MPD operator.
2. Absence of a SCR/kill and choke friction loss procedure related to pump selection on MPD software.
3. Virtual trip tank gain assumed only to be related to mud pump efficiency divergence, without confirming surface back pressure values (which were below limit to impose underbalance).
4. Lack of MPD professionals to attend operations, forcing on-shore coordinator to embark and work as MPD supervisor and coordinator (simultaneously).
5. Poor training on MPD basics, since the operator didn’t understand the consequences of wrong MPD pump selection.

Corrective Actions and Recommendations:

1. Investigation showed that there were 4 different methods for pump selection for kill and choke friction loss operation: one of them would cause a kick (and was the selection that caused the kick of this incident), and 2 others would not cause a kick but would demand a virtual trip tank gain alarm to be banalized. Just 1 of the 4 methods was considered safe by the investigation team.
2. Propose and implement primary kick indicators concerning virtual trip tank gain: it is anti-economic to close the well after every virtual trip tank gain, but there are some situations when it is very likely to have an influx on the well (gain on virtual trip tank associated with very low values of SBP, for instance);
3. It is possible to see a difference between real pump efficiency and MPD software inputted pump efficiency in some situations, despite calibration of pump efficiency on fingerprint. This occurs on low pressure/low flow rate conditions (exactly the situation of the SCR/kill and choke friction loss operation) and can generate a gain on the virtual trip tank that is not caused by a kick. This event was known by the MPD team and contributed to normalizing the observed gain. Adjustments on MPD software pump efficiency have to be done on such occasions.
4. Lack of more SBP specific indicators/limits on MPD control panel showing when the well could be underbalanced, considering extreme cases when there is no flow on drillstring and when there is maximum flow on drillstring. This perception relies solely on the MPD team experience and sensibility towards this important parameter.

safety alert number: 355
IOGP Well Control Incident Lesson Sharing http://safetyzone.iogp.org/

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