Pushing the Limits for Extended Reach Drilling: New World Record From Platform Statfjord C, Well C2

Abstract

Summary Well 33/9-C2 with its horizontal reach of 7290 m is a new world record in Extended Reach Drilling. The well was drilled from the Statfjord C platform in the North Sea, Norwegian sector, and has a total length of 8761 mMD. This paper will describe the planning techniques used, with focus on coping with limitations in equipment and formation. It will also present a case history of the drilling operations including operational experience gained and comparisons between simulated drilling parameters and field data. Introduction The Statfjord field was discovered in 1973. Based on the knowledge and experience at that time, it was expected that it would be possible to drill wells with a sail angle of up to 60 degrees in this area. This resulted in the establishment of three platforms with approximately 5000 m separation. These 60 degree boundaries around each platform resulted in a horizontal reach of approximately 3000 meters at reservoir depth. The northern part of the Statfjord-field, known as North Statfjord, is separated from the main field by a large fault (fig.1). The horizontal distance from the Statfjord C platform to North Statfjord is approximately 5000 meters. Accordingly it was planned to develop this part of the field utilising sub-sea technology. Such a development would cost about three times as much as an Extended Reach solution. More than 100 wells have been drilled from the three Statfjord platforms. The platforms are producing from two reservoirs; the Brent Group and Statfjord Formation of Jurassic age. The first extended reach well with a horizontal reach of more than 5000 meters was drilled from Statfjord C in 1989, well C10[1]. The first well to exceed 6000 m was completed in 1991, well C3[2]. Since drilling began in November 1978 techniques have been developed to push the limit beyond maximum 60 degree inclined wells (fig. 2). The evolutionary process has been based upon a combination of engineering research, application of new technology and field experience. FORMATION RELATED DRILLING PROBLEMS. Because of the many wells drilled in the Statfjord field the possible problem areas are known and attention can be focused on how to overcome these problems, and on which alternative operations can be used to avoid them. Highly Reactive Clays and Shales. Statfjord field stratigraphy shows a high shale and clay content with large proportions of Montmorillonite and Illite which have a large surface area. These characteristics indicate a high potential for the shale to hydrate and swell.

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