A semi-submersible drilling rig chosen to perform the subsea well abandonment. The campaign consisted of abandoning four development wells which were completed with Horizontal Xmas Tree and having sustained casing pressure. In this paper, the methodology for performing the plug and abandonment of each well was divided into four main phases.
Cut and retrieve Tubing
Remediation of sustained casing pressure
The cleanliness of the Chirstmas Tree VX sealing profile is crucial before the deployment of the subsea Blowout Preventer (BOP). A modified wellhead cleaner was created for the efficient cleaning of the VX profile. Caprock restoration was implemented for the effective isolation of the zones with flow potential. Conventional section milling to remediate the sustained casing pressure was eliminated by using Perforate Wash and Cement (PWC). This technology has been widely used by Shell North Sea, where the best practices have been incorporated in the operation.
This paper discusses the "first in the world" application of Dual Casing Cup Type PWC to cement across two annuli. The utilisation of the Tubing Hanger Emergency Retrieval Tool (THERT) to retrieve the Internal Tree Cap (ITC) was deemed more cost-effective as compared to the use of Subsea Test Tree (SSTT).
The design of the Lower Crown Plug (LCP) that was installed in the tubing hanger incorporates an erosion plate known as flow target that was screwed onto the plug by four threads. The flow target from the first well was dislodged and is tightly wedged above the TR-SCSSSV and milling may be required to gain access below the TR-SCSSSV.