Accurate well-path planning is the prerequisite for operators to drill directional or horizontal wells successfully. During directional drilling operations, bit walk objectively exists along an actual drilled well trajectory. Drilling experience shows that it is an effective measure to control a well trajectory by taking the physical bit walk into account if the rate of bit walk can be accurately estimated. As the planned results of bit-walk path can evidently reduce the frequency of azimuth correction and drilling-string trips, and lessen the difficulty and workload of trajectory control, it will undoubtedly improve the rate of penetration and the quality of well trajectory, and cut down the cost of drilling.

The author has published some related methods to plan 3D bit-walk paths, in which the bit-walk rate must maintain constant over each well-path section (build-up, hold-up or drop-off). In some cases, the bit-walk rates are given on the basis of rock characteristics. In addition, it is also an effective measure to determine an appropriate wellhead location, if there is no limitation of surface condition, for the desired profile of a horizontal well. This paper makes further researches on the mathematical model of bit-walk path and gives more concise formulas, analyzes the compositive relation of inclination units and azimuth units, and yields a method to divide them into shorter intervals for calculation. The author discusses the characteristics of planning bit-walk paths and presents the constraint equations and solutions for directional wells. For the desired profile of a horizontal well, this paper also describes the idea and techniques to accurately determine the surface location and a key parameter of the profile, such as KOP, accounting for bit-walk effects. The model and methods provided employs exact mathematical solution and results, and the planned paths are smooth from the wellhead to the given target.

The methods proposed represent significant improvements over the traditional well-path planning techniques, and were programmed into computer software. Several examples are given, and the results proved satisfactory for various directional and horizontal wells.

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