Lessons Learned: Underground Flow Prolongs Well Control Event

Failure to recognize influx leads to large kick volume resulting in underground flow upon shut in.

The underground flow occurred during the drilling of the intermediate hole section—fluid transfers complicated influx detection resulting in kick not being recognized until it was pumped higher into the wellbore.  After it was recognized and secured, the crews didn’t recognize the wellbore broke down above the kicking zone, resulting in an underground blowout. Since the underground blowout was not recognized, traditional well control circulating methods were attempted, prolonging the well control event.  Once the underground flow was identified, the well was killed utilizing a sandwich kill method.

What happened to cause the well control event?
While drilling the intermediate section, encountered abnormally pressured formation and began being kicked. Due to drilling mud surface additions, influx was not recognized until gas units and flow-show rapidly increased. Well was shut-in using the annular preventer and well secured. Crew failed to recognize declining casing pressure (underground flow) and proceeded to attempt a well kill using drillers method with no success. Underground flow developed between a shallower loss zone, water zone and the gas zone encountered deeper. Well was ultimately killed via a sandwich kill.

What went wrong?

• Surface additions of drilling fluid made it very difficult to monitor for gains using PVT system.
  
• Gain/loss alarm was reset multiple times due to surface additions.
  
• 18′ drilling break went un-noticed by drill crew prior to gas reaching surface.
  
• Drill crew did not recognize indications of underground flow once well was secured and attempted to kill using a method which is not suited for underground flow.

Corrective actions and recommendations

• Fluid additions at surface must be monitored closely and hole volume makeup must be calculated to be able to utilize gain/loss as a kick indicator. Preference should be given to mixing fluid in offline tanks and transferring to active system for shorter period of time.

• Industry taught kick indicators went unrecognized. More thorough training and discussions on-site must take place to maintain awareness.

• Once well was secured, drill crew did not recognize casing pressure trends. Further interaction between drill crew and operations team is needed to develop a proper well kill plan.

Content source and credit: IOGP (International Association of Oil & Gas Producers), “IOGP WCI Lesson Sharing 25-7.”