Offshore Norway Case History: First Successful Multilateral Well Installation From a Floating Rig
Authors: Freeman Austin , Gronas Tore , Berge Frode , Durst Doug , Luke Mike 
Published: October 2008

Abstract
This paper details the design, development, testing, and installation of the first successful multilateral well Installed from a floating rig offshore Norway. Well design constraints were evaluated with respect to their impact on a multilateral well. These constraints included rig heave affecting multilateral operations, horizontal junction placement, unconsolidated junction/reservoir rock, and requirements for a cemented junction. Potential problems were determined, and materials and processes were developed to provide resolutions for these problems. Testing was performed to verify that the solutions planned would be successful. New developments for the project included a rate-of-penetration controller tool and a new fluid-loss-control device. Other firsts included the use of a single hollow whipstock to mill the casing window as well as treatment of the junction area with a consolidating chemical to improve stability and reduce the tendency for sand production. Changes to the tools and procedures were identified for future well installations, and these will also be discussed. The multilateral well was constructed according to plan with no serious problems and is currently producing from both laterals. Production data will be presented.

Introduction
The Troll Olje Gas Province (previously Troll West Gas Province) is located approximately 100 km north west of Bergen, in the Norwegian Sector of the North Sea. The water depth is approximately 315 to 340m. Troll Olje is part of the Troll gas field, in which Norsk Hydro is responsible for development of two areas with thin oil rims- Troll Olje Oil Province (22 to 26m oil zone) and Troll Olje Gas Province (approximately 13m oil zone). The combined development is estimated to recover a total of 1.2 billion barrels of 011. See Fig. 1 for an area map and Table 1 for reservoir properties.. Prior to spud of the multilateral well described in this paper, a total of 17 wells had been drilled and completed on the Troll Olje Oil Province. In addition, another 5 wells had been drilled and completed on the Troll Olje Gas Province. Further development of the Troll Olje Gas Province will include another 50 to 60 subsea wells, of which 15 may be completed as multilateral wells. The vast majority of these wells will be tied into a second floating production platform, Troll C, which will be operational by September 1999. The multilateral well concept was introduced on the Troll Olje Gas Province primarily to increase the drainage area from each well. When producing from two separate laterals, there is a lower drawdown pressure throughout the horizontal section, hence, gas coning is less likely to occur, and higher production rates can be sustained for a longer period of time. In addition, there are substantial cost savings associated with the reduced well construction time per horizontal reservoir drainage section and the reduced number of completion strings, subsea wellheads, and pipelines required for the total field development.

Project Planning
The project was initiated with a meeting between Norsk Hydro and Halliburton to outline the requirements for the Troll multilateral well and determine the potential gaps between currently available technology and the project needs. This work was formalized, and a feasibility study was prepared to document the results.