Modeling of horizontal drilling

While majority of today’s oil wells employ directional drilling technology (deviated, extended reach and horizontal wells), a thorough understanding of the drill string dynamics is necessary to increase the drilling efficiency. Wellbore in such wells spans long horizontal distances through the shale to extract oil and natural gas effectively. Very long slender drill pipes transmit the required torque and cutting force through miles of distance from the earth’s surface to the drill bit. Drill string is subjected to different loads and torques which can cause coupled random excitations and failure of its components (drill pipes, bit, sensor tools and wellbore) eventually. If left unnoticed, these vibrations can cause stuck pipe and reduced rate of penetration, both of which are heavily cost dependent. Identifying the conditions causing harmful vibrations hence would significantly reduce cost and time. Controlling the drill string and bottom hole assembly is one way of mitigating the dynamic instability, which is currently done by means of controlling the rotational speed, torque applied and axial force applied to the drill string. This article presents modeling of horizontal drilling and the comparison of horizontal and vertical drill string dynamics. Drill string components are discretized into lumped elements based on their curvature. A vertical wellbore structure with same drill string components is considered for comparison. The computations are performed in MATLAB. Results and discussions are presented in the later part of the report.