Detlef Ragnitz

Advanced Tools for Advanced Wells: Rotary Closed Loop Drilling System - Results of Prototype Field Testing

A new tool (or better a new tool system) is showing up to face the advanced wells challenge in the next years. Having spent the first part of an extensive period of field testing, the system called Rotary Closed-Loop System (RCLS) looks much closer to being run in any extended reach, deep horizontal or complex multilateral well, also in an HP-HT environment. The RCLS was designed to automatically control the well geometry during directional drilling, even while rotating the drill string. The well path is adjusted by hydraulically powered expandable ribs which generate a radial steering contact force to the borehole wall. The amount and direction of the steering force is controlled by the integral downhole electronics, which are capable of steering the well to the desired direction. All parts of the system except a short steering sleeve work continuously in rotation. The RCLS may be operated with or without a downhole motor. Several sub-systems of RCLS have been field tested during 1994 and 1995, e.g., the hydraulic components, most electronic modules, and the bottom-to-surface communication. The first field trial of the complete unit was conducted in late 1995 in a special test well at Montrose, Scotland. Here, for the first time, the full scale of RCLS features was verified, such as the automated steering into any direction as required, the two-way communication link, and the programming of the downhole tool from the surface while drilling. On the basis of findings from this early field application, some technical changes were then made. The field test program was further continued in early 1996 to check RCLS drilling and directional performance with further broadened operating parameters. During the time at Montrose a total of 3,500 ft (1,067 m) have been drilled. The inclination was built from 5° to 71°, and the total drilling time has been 354 hrs. All major functions of the system have been fully verified. One major application of the Rotary Closed Loop System will be to steer wells in extended horizontal sections when steerable motors are difficult to operate. Additionally, because of the elimination of sliding operation together with the precise course correction capability, conventional directional wells will also highly benefit in many cases.