Sustained casing pressure (SCP) in oil and gas wells can result in leakage to the seabed if not properly checked during the final phase of the well life cycle. The escape of well fluid to the seabed as a result of SCP can lead to significant environmental damage, if not properly managed by the operator.

A recently developed innovative technology can drastically reduce the cost of sustained casing pressure mitigation during well plug and abandonment (P&A). The non-removal of the inner casing string before potential SCP sections are milled translates into savings for the operator. This specialty tool is designed to go through riser restrictions and pass through restrictions in the production casing internal diameter to mill the sustained casing pressure section in the intermediate casing. The mitigation of SCP in a single annulus is a challenging operation. In some cases, SCP exists in multiple annuli and can be more challenging because the removal of steel from the well is an expensive operation. The high-expansion section mill has been deployed in combination with improved milling technology in offshore well abandonment and has lowered the cost of well P&A.

The catastrophic impact of losing well barrier elements as a result of sustained casing pressure migration must be prevented. The cost of achieving this in some cases can be more than the cost of constructing a new wellbore. Moving forward, the industry will benefit from this technology by having the ability to mill a casing string section within a section. This capability eliminates the existing practice of performing several cut-and-pull attempts and/or casing milling, followed by a section milling operation.

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