Experience With Drilling C-26A, A World Record Extended Reach Horizontal Well in the Oseberg Field, North Sea.

Abstract

SPE members Abstract Well 30/6-C-26A was drilled to 9327 m measured depth in January 1995 from the Oseberg C platform in the North Sea. The well has a horizontal reach of 7853 m which is a new world record in Extended Reach Drilling. The last 2100 m were drilled horizontally in the reservoir 6 – 8 m vertically above the oil water contact. This paper will describe the planning phase as well as operational challenges experienced during drilling of this well. Introduction The Oseberg Field was discovered in 1979. To develop this 27 × 5 km giant field, two platforms were located 15 km apart. To drain the oil between the platforms two subsea wells were drilled and completed (Figure 1). For the last three years Norsk Hydro together with the partners in the Oseberg Field have put up an overall goal to increase the recoverable reserves by 50 million SM3 (316 million barrels). This corresponds to a final recovery factor of 64 %. Horizontal drilling is one of the most important factors to achieve this goal. The horizontal drilling programme on the Oseberg Field is one of the most comprehensive to take place in the North Sea. The first horizontal well in the Oseberg Field was drilled in 1992. Since then a total of 17 horizontal wells have been successfully drilled and completed. The general trend during this period is that both the length of the horizontal reservoir section as well as the total depth for the wells have increased (Figure 2.). New equipment and technology as well as general field experience played an important role when deciding to go ahead with C-26A. The Oseberg Field Reservoir The reservoir units on the Oseberg Field consist of several sand units within the Middle Jurassic Brent Group (Figure 3). The main reservoir unit is the Oseberg Formation which consists of medium to coarse grained fan-delta sandstones of excellent reservoir quality. The vertical thickness is about 20–60 m and the reservoir qualities are excellent. The Etive Formation overlies the Oseberg Formation. The upper unit in the Brent Group is the Tarbert Formation which is of fair to poor quality and thickness in the south, but is a significant unit in the northern part of the field where the vertical thickness can exceed 40 m. The Ness Formation separates the Tarbert and the Oseberg formations. The Ness Formation consists of delta plain channel sandstones interbedded with overbank fine-grained sediments and coal beds. The channel sandstones are difficult to map from seismic and well data due to their size and scattered occurrence. P. 131