This paper discusses the planning and preparation process for drilling and completing a 10km departure well at the Wytch Farm Oilfield in Southern England.
An 8km departure well was drilled at Wytch Farm during 1995. At the time, this was at the limit of drilling operations. Some fundamental changes involving new technology, operational practices and techniques have been necessary to enable this well to be drilled.
More specifically, the paper will describe the directional drilling techniques necessary to enable the reservoir interval to be accessed. Research and development work performed by the drilling team to identify mechanical limitations in drilling operations at this departure are also examined. This includes a comprehensive review of offset well data to determine friction factors for all operations and concomitant measures adopted to limit rotary torques and drags to workable levels. The other major focus of this paper is to appreciate the mechanism by which drilling muds are lost to the permeable reservoir and describe methodologies employed to overcome this problem.
The paper will also discuss recent experience with the application of partially floating casing, rotary steerable drilling systems and running and cementing long liners.
Completion and intervention challenges are also examined with an analysis of future requirements.
The development of the offshore extension of the BP operated Wytch Farm Oilfield, located on the South coast of Britain, utilising extended reach (ER) wells into the offshore part of the Sherwood sandstone reservoir has been extensively documented in a series of technical papers ,  and . (Figure 1). The current phase of the development is to tap into significant reserves located at reservoir departures in excess of 10km.
The section of the reservoir targeted by this Ultra-Reach well (Measured Depth : True Vertical Depth ratio >5), M-11, lies between 8km and 10km departure from the 'M Wellsite' where the Deutag T-47 rig is located. This site, specially constructed to access the offshore portion of the reservoir currently contains 10 extended reach wells and yields over half of the total 110,000 bopd production at Wytch Farm.
The challenge is to safely and efficiently drill and complete a 10km departure well into the target area to access oil in place of 24mm STB. A single horizontal well into this target is expected to recover some 25–35% of these reserves. Although this is likely to be the most expensive well drilled at Wytch Farm, the significant reserves that it will access are critical to the long term profitability of the field. The well design is the culmination of over a year's evaluation, design and planning, providing an excellent test of the industry's capabilities. Successful delivery of this well will have a significant impact on the industry to access reserves that a decade ago would have required major capital expenditure, in the shape of new facilities, to recover.