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20/12/2007 Drilling efficiency on the Norwegian continental shelf has fallen sharply in recent years. The industry has failed to take adequate account of greater well complexity and risk, claims Morten Mauritzen at ExxonMobil.
Text: Ina Gundersen
“We’re spending more time on drilling than planned,” admits Mr Mauritzen, who is responsible for partner-operated fields on the NCS at the US oil giant.
He points to an overhead showing the trend for drilling efficiency on fields where ExxonMobil has interests, and expresses concern over developments in 2007.
The gap between actual and planned time to drill wells on the NCS in which the company is a licensee has increased sharply. The 17 wells in which it participated during the first six months took more than 50 per cent longer than expected, for instance.
This means that 6.8 rig-years were used instead of the intended 4.4 – an overrun of 2.4. That corresponds to the “loss” of eight to 10 wells or a production shortfall of close to 100 000 barrels of oil equivalent per day.
“We must recognise that drilling and completion have become more complicated than before,” Mr Mauritzen concedes. “That means we have to get better at identifying risk, planning on that basis and executing a programme which takes it into account.”
Wells are more difficult than they were a few years ago – longer, deeper and often drilled under high pressure and temperature. And more drilling is being pursued in mature fields.
“Drilling through depressurised zones in mature fields represents a challenge because reservoir conditions are less stable,” explains Mr Mauritzen.
“Where multibranch wells are concerned, I’d question whether we’re good enough at balancing their complexity against expected supplementary resources.
“Perhaps we should sometimes drill shorter and simpler wells so that we could free up rig time to focus on new drilling targets.”
He believes that understanding of technical risk has deteriorated, at the same time as the technology is being pushed to its absolute limits.
“Expertise has become a constraint on both contractor and operator. Overall experience available on a rig is often lower than before for each well drilled – more crew are both younger and less trained.
“With hindsight, we’ve seen too many examples where inadequate understanding of technical risk causes major but avoidable operational problems. In the worst case, we’ve had to plug the well and drill a sidetrack.”
Mr Mauritzen notes that the industry in Norway must compete globally for capital, rigs and equipment. Rig capacity is almost fully utilised, equipment gets worked harder and longer, and lengthy delivery times apply for spares.
“The sum of these changes and results show that we haven’t assessed the total complexity and risk in an efficient manner,” he says.
ExxonMobil participates annually in more than 1 000 wells on a global basis, and is operator for over 80 per cent of these. Mr Mauritzen says that its Norwegian arm can draw on this experience to improve results.
“We carefully categorise the risk of each well to be drilled in order to improve our understanding of its complexity.
“Our requirements for reviewing equipment and drilling procedures are particularly stringent for complex wells, and this work is cross-disciplinary.
“That means our drilling and sub-surface teams must cooperate closely to achieve a shared understanding of the risk before a decision is taken.
“Detailed involvement by senior management in the various disciplines is essential. And we can point to good results from this approach.
“We’ve drilled on Ringhorne in the North Sea since 2002, with no deviation overall between the actual and estimated time used.”
A detailed review and cost/benefit analysis is also crucial before adopting new technology, or at each stage when existing technology is being stretched.
Establishing priorities for every drilling opportunity is important in ensuring that rigs and resources are utilised in the best possible way, Mr Mauritzen says.
“Efficient processes at the companies for rapidly identifying and adopting best practice across organisational and national boundaries are highly significant.
“In addition, we must ensure an exchange of experience between organisations and specialist teams. Our central drilling group in Houston plays a key role in facilitating that. This means it’s a short way from Malaysia to Norway, for instance.”
Read more about some of these challenges and how they could be overcome: