Problems had arisen with the same producer in December 2009 and March 2010 before the most serious incident occurred in the afternoon of 19 May 2010.
Control of pressure in the C-6A well was suddenly lost, the mud column vanished, and the alarm was sounded.
“This event was very serious,” emphasises PSA supervision coordinator Hanne Etterlid.
“Under only slightly diff erent circumstances, it could have turned into a major accident.” Work on restoring control over C-6A and re-establishing its downhole barriers lasted for more than two months.
The PSA’s investigation of the incident identified serious defi ciencies in Statoil’s planning of the drilling and completion operation in this well. Management checks that activities were being conducted satisfactorily were also inadequate.
These shortcomings related to key conditions such as risk management and change control, as well as experience transfer and the application of expertise.
Familiarity and compliance with the operator’s own governing documents as well as documentation of decisions taken were also found to fall short.
These serious fi ndings resulted in a far-reaching order to Statoil, including a requirement to review and assess processes related to well work on Gullfaks.
The company was also required to establish why measures initiated after the serious gas leak on Snorre A in 2004 failed to have the desired eff ect on Gullfaks.
“We take the view that the C incident could probably have been avoided if Statoil had learnt from earlier mistakes and drawn on available expertise in-house,” comments Ms Etterlid.
“A key job for the company is accordingly to find out why it has failed to apply the lessons provided by earlier incidents.”
The PSA has questioned whether Statoil is making suffi cient eff ort to seek out and evaluate the underlying causes of the errors made.
“It’s important for us that all aspects of the order are assessed and dealt with, so that specifi c improvements result,” emphasises Ms Etterlid.
“That includes Statoil achieving genuine learning and experience transfer, both on Gullfaks C and on other installations where necessary.”
The Gullfaks C incident has also helped to illustrate the challenges posed in complying with the regulatory requirement on drilling programmes for relief wells.
According to the regulations, such plans are required for every well drilled on the NCS. The operator must keep them updated in line with reservoir changes and new technology or methods.
The PSA intends to monitor the industry’s work both on relief wells and on overall strategies for emergency response to downhole problems.
This article was published in the publication "Safety - status and signals 2010-2011".