Several cases have recently been seen where challenges are posed by the design of individual wells and the opportunities to kill them with a relief well. To get room for all the downhole equipment desired and to ensure maximum output, such wells are planned with a wide diameter on entering the reservoir and with the final casing string set much higher up.
Simulations of pressure and flow rates, to document that a possible blowout could be halted, frequently show that two relief wells would be needed for success.
In the event of an uncontrolled blowout, a relief well must represent a genuine last resort and no uncertainty may exist about its ability to quench the flow. Globally, only one instance is known of a kill operation being conducted with the aid of two relief wells – and that occurred on land.
Given the challenges of drilling two such wells offshore on the NCS, the PSA has questioned whether such an approach would be acceptable. It invited representatives to a two-day working meeting in August to gather information on and knowledge about industry practice in this area. Participants in this session included specialists on well design, cementing and killing from oil companies, contractors and consultancies.
The meeting revealed that a number of conditions need to be clarified with regard to well design and relief drilling. This issue will continue to be pursued by the PSA, which will assess whether changes are required to the Norwegian regulations and relevant industry standards. Drilling a relief well could be the last chance to halt a blowout, so plans for such an operation must be reliable.