Abstract
Slimhole drilling has long been regarded as means to reduce drilling costs and environmental effects through economies of scale and reduction of produced drill cuttings. However, its potential benefits have often been lost because of poor drilling performance and lack of well-placement capability in smaller holes. This is particularly true of brownfield environments, such as the North Sea, where tortuous multiple-target well paths require accurate and predictable directional capability in often-depleted reservoir sections. The development and effective deployment of a slim-hole rotary steerable system, (RSS), has changed this dramatically. Since initial field-testing in mid-2002, more than 30,000 ft of 6-in. hole has been drilled in the UK Continental Shelf alone. Performance has been exceptional, with average timesavings of over 60% compared with conventional drilling systems. Typical of this are wells on Shell U.K. Exploration and Production, (Shell Expros'), Brent and Cormorant Alpha fields, where up to 4850 ft has been drilled with near perfect well placement in a single run. Continued reduction of mature asset well costs through successful applications like these makes slimhole mature asset drilling economic and has the potential to extend drilling activity, field life and hence increase the ultimate recovery of the field.
