TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractKristin is a HP/HT field developed on Haltenbanken offshore mid-Norway. The Kristin development consists of 4 templates with a total of 12 subsea wells. The inclination through the reservoir ranges from 28 to 85 degrees. The reservoir at approx. 4600mTVD (15092 ft) has an initial pore pressure corresponding to 1.96sg EMW (16,36 ppg) and a temperature of 172°C (342°F). With a water depth of approx. 360m (1181 ft), a MW of 2.05sg (17,11 ppg) is needed to be able to maintain a riser margin. Three different drilling fluid systems have been used in the reservoir section: 1) Cs/K-COOH clear brine system. 2) Invert emulsion HP/HT OBM. 3) Invert emulsion HP/HT OBM with ultra fine weight particles. Challenges such as ECD management, hole stability, formation damage, weight material sag and operating on subsea HP/HT wells during harsh winter conditions had to be addressed both in the planning and the operational phase. In this paper the background for selection of the drilling fluid is briefly described and especially the rationale behind using three different systems. The paper highlights operational experiences to illustrate how the drilling fluid systems influenced and coped with the challenges of drilling subsea, high angle HP/HT wells. The paper provides a discussion of the pros and cons of the different fluids systems. Finally the paper identifies some of the challenges that lie ahead as the production has started and the reservoir starts to deplete.

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.