Abstract
For a design of deviated well trajectory, it is important to estimate torque and drag and to select the most appropriate well trajectory. Some equations of torque and drag have been proposed under an assumption that torque and drag forces are primarily caused by sliding friction. However, since they are formulated as an incremental equation using short element of the pipe, they have a little short versatility, i.e., necessity of computer usage. Under an assumption that azimuth angle and inclination angle do not change together over a bending section, the incremental equation can be transformed to differential equations. Based on conducted differential equations for three bending sections, theoretical formulas for inclination angle change section and approximate formula for azimuth angle change section are both derived as algebraic equation. These formulas can easily calculate torque and drag using only bending condition parameters. It is found that the proposed formulas can be used as a convenient estimating method, since the estimate for hookload including drag agrees well with one obtained by conventional iteration of the incremental equation.
