Rotary-steerable technology is progressing rapidly all over the world because of the improvements in hole cleaning and torque-and-drag. It works well especially in extended-reach drilling and holds great promise in directional work.

In rotary-steerable drilling operations, bit walk objectively exists along an actual drilled well trajectory. The drilling experience shows that it is an effective measure to control a well trajectory by use of the physical bit walk. The authors developed a method to plan various bit-walk paths with any combination of arc and straight sections in the vertical expansion plot.

The authors also presented a method to calculate a drilled well bore trajectory directly using the rates of inclination change and azimuth change for rotary-steerable drilling. Compared with the radius of curvature method and minimum curvature method, the most commonly used methods in the oil field, the improved method of survey calculation yields more accurate and stable results.

When a well trajectory deviates from the planned path, the driller must make a path correction and the correcting section has to employ a 3D trajectory to hit the predetermined target. Existing methods for planning 3D trajectories are available, but their objectives are only to hit the expected targets. In some cases, however, adjusting the trajectory to the preferred direction is more important than only reaching the target. For example, when drilling horizontal wells, engineers must focus on trajectory direction to land the build-up section successfully and continue drilling the horizontal lateral. The authors proposed a method to make a soft landing of well path, which yields a well trajectory that reaches the expected target from a specified path direction, with no need for trial- and-error procedures.

In a word, the methods in this paper represent significant improvements over the traditional well-path planning and survey calculation techniques, and were programmed into computer software. The results proved satisfactory for directional and horizontal wells in China.

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