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.

Tools and Techniques for Plug and Abandonment

“…In a sand cutting technique, a high volume of particles are pumped at low pressure; however in abrasive water jet cutting, a low volume of solid particles are pumped at high pressure [22].…”

Vehicle routing with endogenous learning: Application to offshore plug and abandonment campaign planning

“…Among other functions, the rig provides capacity to handle fluids returns as well as heavy lifting and cutting operations. However, more recently, lighter vessels are being used to perform simple P&A operations (Saasen et al, 2013;Sørheim et al, 2011;Valdal, 2013). This includes Riserless Light Well Intervention (RLWI) Vessels and Light Construction Vessels (LCVs).…”

Essential Aspects in Probabilistic Cost and Duration Forecasting for Subsea Multi-well Abandonment: Simplicity, Industrial Applicability and Accuracy

“…More recently, abrasive water jet technology has been used. This system can be deployed from a vessel and complete this stage of P&A (Sørheim et al 2011;Saasen et al 2013). This stage aims to remove all obstructions related to oil and gas activities from the seabed such that no obstacles are left on the seabed causing problems for other marine activities like e.g.…”