Abandonment of Offshore Exploration Wells using a Vessel Deployed System for Cutting and Retrieval of Wellheads

Abstract Plug and Abandonment (P&A) can contribute with 25% of the total drilling costs of exploration wells offshore Norway. Cost efficient P&A technology is therefore necessary. In this paper, qualified technology for cutting and retrieval of wellheads using a separate vessel is described in detail. It is shown how to use this technology to significantly reduce the costs of exploration drilling. The technology has now been used on several abandonment operations on the Norwegian continental shelf. During the P&A phase of the North Sea offshore exploration well, Trolla, the rig was unable to pull the 9-5/8" production casing and was therefore unable to secure and abandon the well according to plan. This incident prevented the wellhead from being retrieved in accordance with Norwegian legislation. The required barriers were reestablished by squeezing cement through cuts in the production casing. Then the well was permanently plugged; leaving the wellhead temporarily abandoned by installing a trawl protection. This is used while waiting for a vessel to arrive for completing the operation. A high pressure abrasive water jet cutter was run from this vessel. The abandonment operation with this vessel, the world's deepest multistring conductor cut using such a system, was successful. It is shown how the casing was cut, and how the complete wellhead including the guide base was retrieved with the vessel active heave compensated crane. On a different Norwegian Sea well, a spud foundation "can" was used at a water depth of 274 m MSL to preinstall a wellhead foundation on the seabed. The paper show how the surface casing was cut approximately 12.5m below the top of the wellhead by using water jet cutting technology and how the wellhead together with the can was retrieved in the P&A operation.