A recent lesson shared by the Well Control Incident Subcommittee of the IOGP (WCI Lesson Sharing 21-6) underlined the risk of taking a meter reading at face value when in reality, data ‘validation’ technology embedded in software led to a dangerous false reading. The issue occurred during the drilling of a deepwater exploration well using managed pressure drilling (MPD). During drilling, a rapid increase in flow out was observed, in reality at a rate of 3,000 gallons per minute. Unfortunately, software controlling a Coriolis meter that should have shown the abrupt change included some rather arbitrary determination as to what constituted ‘good’ data. A ‘data validation’ step in the meter flow out considered values less than zero and over 3000 gpm to be ‘bad data’.
Consequently rig personnel believed that flow out and attributed the increasing surface back pressure to a plugged choke. The ‘zero’ flow out value meant that kick detection logic failed to spot the kick since the surge occurred between the 20 second trend detection interval. Fortunately, other indications of the kick led to the well being safely shut in. But, as the IOGP points out, ‘If just one or two actions had been different or perhaps, just slightly slower, the outcome may have been much more severe than just time spent recovering from an influx’.
The IOGP makes several recommendations resulting from this near
miss. These include ‘understanding the logic used in the MPD software
and ensuring that conventional flow detection is available for MPD
operations’. More generally, IOGP links this incident with other well
control events where ‘root causes were associated with lack of
understanding of the technology and associated procedures, leading
individuals to forget basic rules such as shutting-in a well at the
right moment in time.’ As a result, IOGP has brought collected its
analysis of such incidents and advice on a new publication, Managing the introduction of new technology in well operations. More too from the IOGP Safety Zone minisite.
Comment: Suggesting that those involved in well design or rig personnel be cognizant of the code used in the control system is a big ask! It would be better if IOGP communicated details of the meter software (manufacturer, version number) so that other operators could check to see if they are also at risk. We put this to IOGP which replied … ‘When gathering and reporting information on safety incidents, both actual and high potential, as part of IOGP’s safety data collection program, the Well Control Incident reporting program, or other, we do not specify the names of products or services, whether it’s software, a piece of equipment, or a service provider. This information may or may not have been specified in the original report. If it were, it would not be shared with the wider Membership’.
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