Torque Reduction Techniques in ERD Wells

Abstract

Abstract World class ERD wells are being used in the Russian Far East to develop an offshore reservoir from an onshore location. These wells have reaches of 9-11 km. While drilling the initial wells into the reservoir, high torque was experienced even while using a nonaqueous drilling fluid (NAF). The torque was sufficiently high that concerns arose about the feasibility of being able to drill longer wells later in the development. Consequently, finding techniques to reduce drilling torque became a major focus for the drilling phase of the project. A systematic R&D process was initiated to look for solutions to the torque problem. The scope of the investigations included consideration of different drilling fluid base oils, solid/liquid lubricants, and mechanical means to reduce torque. Small-scale screening lubricity testing was performed in a controlled laboratory environment to identify potential lubricant candidates. Full-size laboratory testing was then performed on the leading products. Various mechanical means to reduce torque were also evaluated. Finally, field trials were performed using solid and liquid lubricants and different types of mechanical torque-reduction tools. Solid lubricants caused plugging problems with BHA components and their use was discontinued. Liquid lubricants achieved torque reductions of 5-15%, which was sufficient to drill the longest throw wells. The mechanical tools when added to the drill string showed the greatest reductions in torque, but were very expensive. Since the liquid lubricants represented a significant addition to the cost of the wells, other means of reducing torque were investigated. Eventually, it was discovered that the use of 4,500 m of range II drill pipe instead of range III caused a reduction in the torque. This is believed to be related to the larger tube body-casing contact area of the range III pipe joints compared to the range II pipe joints. Further evidence that the large contact area between the casing and the range III drill pipe was causing both excessive wear and torque was provided when drill pipe inspections revealed an alarming increase in rejections due to excessive tube wear near the middle of many joints. Ongoing investigations are attempting to find mechanical solutions to the drill pipe-casing contact problem. New orders of drill pipe could be range II pipe, but the existing large inventory of range III drill pipe needs to be protected from excessive wear, while at the same time reducing the drilling torque. Several types of drill pipe stand-off bands are under investigation and may represent a viable solution to both problems.