Novel Mechanical Tool for Running, Locking, and Retrieval of Subsea Tree to Wellhead

Abstract Hydraulic tree connectors can be vulnerable to hydraulic failures. This paper describes a newly developed tree connector mechanical running tool (TCMRT) that is designed to mechanically perform locking and/or unlocking of a hydraulic tree connector to the wellhead to significantly reduce nonproductive time in the event of hydraulic failure. Two cylinders are associated with the TCMRT, which can apply a locking force of 2.4 million lbf in the downward direction, enabling the tree connector to be mechanically locked onto the wellhead. They are also capable of providing an equal load in the upward direction, which helps to mechanically retrieve the tree from the wellhead without using the hydraulic system. The development of the mechanical locking method expedites tree installation in the event of hydraulic failure. Ultimately, the tool prevents the entire system having to be returned onshore for rework in the event the tree connector's hydraulic system fails. The design was validated using theoretical calculations and finite element analysis. It was tested successfully in a laboratory environment, where offshore load cases were simulated. The TCMRT can be operated on both wire and drillpipe, enabling trees to be installed using both rigs and light vessels. No matter where the hydraulic issues might have occurred, there are no limitations on using the tool to continue operations. In June 2024, the tool was first transported offshore along with the tree system. During the design and execution phases of the project, many operators actively participated in the development and first successful testing of the tool. The mechanical locking system provides a novel method of locking a hydraulic tree connector onto the wellhead by supplying an extremely high mechanical load, enabling tree installation to continue even when hydraulic failure occurs. The tool can also provide operators with an option to control the locking load by using the tool along with the hydraulic method, which helps reduce the load passing through the hydraulic system based on an operator's preload requirement.