A new orientation design model and numerical solution for coiled tubing drilling

• A new two arc orientation model was proposed for tool-deflection orientation.
• Solving the proposed model provides single true solution corresponding to field conditions.
• The new model enhances adherence to planned well trajectory for coiled tubing drilling.

Coiled tubing cannot be rotated in the wellbore from the surface, thus, an orienter is used to steer it in the proper direction. Due to the limits of rotation mode, bottom hole assembly (BHA) can only be rotated in increments in one direction at a fixed angle. As a result, the actual tool face angle is not equal to the design angle in most cases. The difference in the angle will affect the coincidence rate of the drilling trajectory, potentially causing orientation failure. The traditional method for adjusting the weight on the bit (WOB) is to eliminate the angle deviation. However, the change in the WOB is completely dependent on the expertise of the directional engineer and the formation parameters. This dependence limits the applicability of this adjustment method and increases the uncertainty and construction risks during the drilling process. To solve this problem, a new two-arc orientation design model is proposed that meets the orientation requirements and is easy to operate on site. Compared with the traditional experience-based method, this new method avoids uncertainty from human factors and can be programmed for automated drilling.