Many oil and gas operators around the world are faced with drilling operational risks when entering the matured field phase. Narrow drilling margins, hole collapse and lost circulation are among the challenges that must be dealt with safely and economically.This paper describes a successful approach to overcoming these challenges developed through close cooperation between the operator and the oilfield services company. By providing an overview of the concept, technology and operating principles of the 9 ⅝ in and 7 in advanced steerable drilling liner system, the paper highlights the development and the testing process leading to the successful execution of the world's first steerable drilling liner application in the Norwegian sector of the North Sea.The paper also discuss description of the testing and qualification of the two liner drilling sizes (9 ⅝ in and 7 in) at the service company's experimental test rig.

Drilling in the Statfjord Field has become increasingly challenging as remaining oil pockets require designer wells, horizontal wells, or Extended Reach Drilling (ERD) wells with great demand for reservoir navigation in three dimensions. Until recently this has been performed with steerable motor assemblies, with frequent steering difficulties in the reservoir sands. Low rate of penetration (ROP) while sliding has given an overall low drilling efficiency, and in some cases inadequate steering ability has resulted in a less than optimum wellbore placement. Long sliding intervals have also resulted in poor hole cleaning, which has contributed to stuck drill string and lost circulation problems. This paper presents the introduction of a rotary steerable system in the multilateral horizontal well C-23 in the Statfjord Field, and how this improved drilling performance over comparable wells in the reservoir. The following topics are discussed in the paper:–Field description and brief overview of directional drilling challenges in the Statfjord Field.–Statoil's active role in the development of rotary steerable systems.–Functional description of the rotary steerable system, highlighting the technology's benefits compared to traditional directional drilling methods.–Why well C-23 was chosen as a suitable candidate for therotary steerable system, becoming the first successful utilization of this promising technology in the Norwegian Sector.–Case history, emphasizing directional control, drilling efficiency improvement, and other valuable experiences from utilizing the rotary steerable system. P. 313

The well 34/8-A-6 AHT2 was drilled from the Visund Field Floating Production and Drilling Unit (FPDU) in the North Sea, and set on production in October 2005. The well was drilled to 9082 m/29796 ft measured depth and has an Along Hole Depth (AHD) reach of 7593 m/24911 ft, which is a world record for Extended Reach Drilling (ERD) from a floating installation. The 34/8-A-6 AHT2 is also the longest Down hole Instrumentation and Control System (DIACS) installation worldwide, with the lower isolation packer set at 8560 m / 28084 ft measured depth. The well includes three hydraulically operated flow valves, which are used as down hole chokes to optimize the production from the separate zones in the reservoir. Subsea developments in combination with ERD wells can increase oil production and lower total development cost. The drilling progress was 108 m/day from seabed to total depth, according to the Rushmore drilling performance definition, and the payback time for this well was less than two months. Experiences gained on this well indicate that even longer wells can be drilled from subsea locations in the near future. Introduction The Visund field is located in block 34/8 in the North Sea 150 km west of Norway (Figure 1, 2, 3). The field was discovered in 1986 and production started in 1999. The Visund field is an oil & gas field, with a water depth of 335 m (1100 ft). The depth of the main reservoir is between 2900–3000 mTVD, with a maximum pore pressure of 434 bar. The field is 24 Km long and 4 Km wide. With this shape of the field, ERD wells drilled both to the North and to the South will increase drainage area and thereby the total recovery from the field. The Visund Floating Production and Drilling Unit (FPDU) is located centrally on the field. The Visund North satellites consist of two wells tied back to the FPDU with a 9 km long subsea pipeline. The well in this case history is a world record ERD well drilled from a floating installation. In the early pre-planning phase, the well was planned as a separate costly subsea development, drilled by a separate semi-submersible rig. A new technical and economical study showed that this well could be drilled more economically from the existing Visund FPDU, using existing subsea systems. The total depth of the well 34/8-A-6 AHT2 is 9082 m. The horizontal reach (slot to TD) is 7484 m and the along hole depth (AHD) reach is 7593 m, - a world record reach from a floating installation. (Figure 4, 5, 6) Low friction factors in relation to torque were experienced by the use of an optimum well profile. Good hole cleaning was obtained with the use of 180 RPM on the drillstring together with maximum allowable flow rate. The ERD well has a Down hole Instrumentation and Control System (DIACS) completion with tree separate zones, operated by three hydraulically controlled flow valves. This is the longest DIACS completion in the world, with the lower isolation packer set at 8560 m. The well is produced at a rate of 2500 Sm3/day (15700 bbl/day) with production from all zones. Production from the upper zone A would not have been possible without a controlled production from the other zones, hence adding value to the DIACS completion design Experiences from this well show that even longer wells can be drilled from subsea locations in the near future. Optimal pre-planning with use of all service companies involved in detail planning and risk identification workshops are a critical factors for success. In the operational phase the work in the subsurface team was optimised through using 3D visualisation tools. These 3D tools facilitated in getting a common understanding in the whole team, which was used to optimize the reservoir pay zone drilling of the well. Subsea developments in combination with ERD wells can increase oil production and lower total development cost, in comparison to costly additional subsea systems that need to be installed prior to drilling a new well.

TX 75083-3836, U.S.A., fax 1.972.952.9435. AbstractThe well 34/8-A-6 AHT2 was drilled from the Visund Field Floating Production and Drilling Unit (FPDU) in the North Sea, and set on production in October 2005. The well was drilled to 9082 m/29796 ft measured depth and has an Along Hole Depth (AHD) reach of 7593 m/24911 ft, which is a world record for Extended Reach Drilling (ERD) from a floating installation.The 34/8-A-6 AHT2 is also the longest Down hole Instrumentation and Control System (DIACS) installation worldwide, with the lower isolation packer set at 8560 m / 28084 ft measured depth. The well includes three hydraulically operated flow valves, which are used as down hole chokes to optimize the production from the separate zones in the reservoir.Subsea developments in combination with ERD wells can increase oil production and lower total development cost. The drilling progress was 108 m/day from seabed to total depth, according to the Rushmore drilling performance definition, and the payback time for this well was less than two months. Experiences gained on this well indicate that even longer wells can be drilled from subsea locations in the near future.

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