The spiral steel pipe is drilled in rotation and begins to enter the soft formation. Under the action of the tritone, the drill bit first produces elastic shear deformation of the formation and then is removed under the pressure of the tritone. In the simulated environment, the soft soil is homogeneous clay, and the formation and cracks in the soil are not considered. Horizontal directional drilling is performed in abrupt formations where the formation is in random dynamic contact with the roller cone bit. Friction occurs when the cone comes into contact with the formation. The impact force makes the spiral steel pipe vibrates. When the three-cone bit moves from soft formation to hard formation, it will inevitably produce large lateral vibrations and up and down the vibration.
When the drilling speed is 0.008m/s and the bit speed is 2 radians/s, the pseudo-strain energy curve during the propulsion process of the roller cone bit mainly includes viscosity and elasticity. However, since the viscous term usually dominates, the conversion of most of the energy into pseudo-strain energy is irreversible. The deformation energy of the spiral steel pipe is the main energy consumed to control the hourglass deformation. If the pseudo strain energy is too high, it means that the strain energy controlling the deformation of the hourglass is too large, and the mesh should be refined or modified. To reduce excessive pseudo-strain energy. The pseudo-strain energy mutation in this model mainly occurs when the drill bit enters the soft soil layer and the roller cone bit passes through the abrupt formation interface. The harder the formation, the greater the pseudo-strain energy of the drill bit entering the formation. Simulate the drilling process of the spiral welded pipe in the abrupt formation, and predict the change of the drilling trajectory of the drill bit.
(1) The sudden change of pseudo-strain energy mainly occurs when the drill bit enters the soft soil layer and the roller cone bit passes through the abrupt formation interface. The higher the forming hardness, the greater the pseudo-strain energy when the spiral steel pipe enters the forming process.
(2) When drilling into the formation suddenly, the spiral steel pipe moves longitudinally, and the drill bit vibrates. The harder the formation, the greater the bit vibration.
(3) Under the condition of a certain formation dip angle, the greater the drilling speed of the drill bit, the greater the longitudinal deviation of the drilling trajectory, and the greater the drilling speed, the smaller the longitudinal deviation of the drilling trajectory. When the bit rotational speed is lower than 2.2rad/s, the influence of the rotational speed on the longitudinal deviation of the drilling trajectory decreases.
(4) At a certain bit speed, when the local formation dip angle is 0° and 90°, it does not affect the drilling trajectory; when the local dip angle gradually increases, the longitudinal deviation of the drilling trajectory increases; when the local dip angle exceeds 45°, the impact on the longitudinal deviation of the drilling track is reduced. The research results in this chapter are of great significance for improving the prediction accuracy of the tritone bit's drilling trajectory in steep formations and lay a theoretical foundation for correcting the drilling trajectory of the spiral steel pipe through the horizontal pilot hole.
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