The Weekly Reflektion Week 20 / 2020

In the previous weeks’ Reflektions we have discussed the importance of ‘resilience’ and an organisation’s ability to adapt to be able to manage a hazardous situation that was not anticipated. We have also suggested some techniques to develop resilience in your organisation. This week we will look at the resilience of the offshore team on the Snorre A platform when a blowout occurred in 2004.

During work on well P-31A on Snorre A on 28 November 2004, a gas blowout occurred, with breakout on the seabed resulting in gas on and around the platform. The Snorre A platform is a tension leg platform in the Norwegian sector of the North Sea. The incident occurred during a well workover when a length of casing was being pulled out of the well. The suction caused by pulling the casing (swabbing) drew gas from the reservoir into the well bore and the gas found its way through a leak in the casing to the formation outside the well. The gas leak could have resulted in an explosion. The gas also eroded the seabed around the suction anchors that the platform tension cables were tethered to. The erosion could have compromised the suction anchor integrity and resulted in stability problems with the platform. The Petroleum Safety Authority (PSA) described the incident as one of the most serious on the Norwegian Continental Shelf.

Investigations into the Snorre A blowout in 2004 were carried out by Statoil (now Equinor), the operator, and by PSA. The PSA report is available on the PSA website and the causes of the incident are described in this report. The incident resulted in a situation that the offshore personnel had never faced before. The incident could have led to an explosion and fire or to a stability failure and potential loss of the platform. The offshore team assessed the situation and the risks to themselves and the platform and decided to take remedial actions to kill the well and stop the gas leak. Their actions were ultimately successful.

The first step was recognition and interpretations of many signals to understand the hazards. Gas was detected at several locations on the platform, around the platform and in the cooling water system (due to gas drawn into the seawater lift pumps). The potential effect of the gas on the suction anchors and the possibility for a stability failure was also recognised as a threat. Non-essential personnel were evacuated from the platform as a result of the hazards.

The second step was understanding the potential limitations in the systems and equipment. The BOP shear rams and pipe rams were unavailable since the casing (scab liner) across the BOP at the time was not shearable. The main power was shut down due to the gas around the platform, and the lack of power limited the drilling system functions available, and therefore the options for killing the well. There was also potential for gas ingress to the air intakes on the diesel-driven cement pumps that may be required in the remedial actions. The potential ingress of gas to the platform ventilation system was also a threat.

The third step was the assessment of the remedial measures to kill the well and the material and resources required. The offshore team had three options, kill the well with drilling mud, attempt to plug the well with cement, or bullhead the well with seawater at a high rate to stop the gas leak.

The fourth step was the assessment of the risks and how the risks may change as the incident progressed. This process was particularly important since the individuals involved were directly exposed and their ‘buy in’ to the risk exposure was essential for them to be able to carry out their tasks. Two key factors in the management of the risk was the assessment of the control that the offshore personnel had and their consideration of their escape and evacuation possibilities if they lost this control.

The knowledge of the Snorre systems and how they could be modified and adapted to be used safely in this hazardous situation and the ability to work together in difficult circumstances were critical to success.

Careful monitoring of the gas concentrations around the platform gave the team confidence in what equipment could be used without fear of ignition. The start-up of the power generation was needed to be able to operate the equipment to pump drilling mud to kill the well. 
Dismantling of equipment on the top drive was required to allow access to a manual valve, pick up a kill stand, and strip  the pipe (scab liner) into the well, to be able to use the BOP pipe rams, and, if necessary, the shear rams  to secure the well. Modifications to the air intakes on the cement pumps were required to prevent gas ingress to the diesel engines.  Modifications to the ventilation intakes were made to allow cooling of critical systems. The quantity and characteristics of kill mud that could be mixed was limited by what was available on the platform since additional materials could not be provided from supply boats due to the gas around the platform.

The offshore team managed to kill the well with only a few barrels of mud left. They still had the options of pumping sea water and bullheading cement into the well. Some people may consider that the offshore team got lucky. As Gary Player the South African golfer was once reported to have said. ‘The harder I practice, the luckier I get’.

The offshore team’s success in killing the P-31A well on Snorre A is a worthwhile case study in resilience and could easily be adapted to a ‘what if’ scenario that could be used by your organisation. 

Reflekt AS