Eliminating Sustained Casing Pressure in Well Abandonment

Abstract

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. Objective/ScopePressure generated within an annulus by thermal expansion of wellbore fluid during production is called annular pressure buildup (APB). APB can be bled off in platform and land wells, and it does not rebuild afterwards.The objective of this paper however is to address the challenges of sustained casing pressure (SCP) in well abandonment occurring from the rebuilding of casing annulus pressure after bleedoff. Sustained casing pressure is not caused solely by temperature fluctuations or pressure introduced in the well by the operator. Subsea wells have no penetration through the high-pressure wellhead housing for annuli B, C, D and other annuli that may exist in the well. The casing shoes are left open and can serve as a pathway for SCP in the casing annuli. The open casing shoe mitigates the annular pressure buildup due to

Design and field-scale demonstration of the buoyant-kill process for restoring integrity of wells with sustained casing pressure

“…One of these techniques, drilling through inner casing for squeeze cementing has proved to be highly unreliable even after many trials (Bourgoyne et al, 2000). Another technique of milling a section of the inner casing for placing cement plug to intercept gas flow has also been more effective (Obodozie et al, 2016) but still unreliable in wells with eccentric inner casing due the unknown size of the milling tool (Milanovic and Smith, 2005). An ultimate (and very costly) technique involves cutting off and removing the upper section of the inner casing to replace the leaking cement.…”