In the drilling process of a horizontal well, the large drilling friction between the drill string and the wellbore wall can cause the phenomenon of backing pressure and reduce drilling efficiency. To reduce the drilling friction, a new anti-friction tool is proposed and then dynamics and anti-friction characteristics of the horizontal drill string are studied. According to the actual working conditions, the force analysis of the drill-string system is conducted. The dynamics model of the drill string is established and the vibration anti-friction characteristics of the drill string are studied. The numerical solution method is used to solve the dynamics model and the experimental test is conducted to verify the structural design of the new anti-friction tool. According to the theoretical calculation results, the variation law of the average friction, the vibration characteristics, and the bit rotation velocity response under different initial conditions are obtained, and the experimental test result shows that a new anti-friction tool can generate axial vibration. Through the theoretical and experimental study, the design and development of new downhole anti-friction tools can be improved, which is beneficial to solve the problem of large drilling friction in horizontal wells and can provide technical support for high-efficiency oil and gas well drilling.

Aiming at the problems of large torque fluctuation of drill bit and low weight-on-bit(WOB) transmission efficiency during the drilling process, a novel drilling tool generating constant torque and reducing stick-slip is proposed. For investigating the further dynamics behavior of drill string system, the mathematic models are established based on the new tool output characteristics. Also, compared with field test and application, the drilling tool effects on increasing ROP (rate of penetration) and reducing drill bit wear are verified. The research results show that the peak value of drill bit angular velocity increases gradually with the bigger value of the pre-compression of disk spring system, so as the rotary table inputting speed, during drill bit downward movement. About the drill string influence, the larger the length of drill string, the longer response time is the rotating angular velocity of drill bit. Another one, the shorter the steady time of drill bit angular velocity, the bigger ratio is the stick-slip within one period. This new drilling tool can effectively improve the drill bit force conditions, and reduce the stick-slip stage, which can also profitably increase drilling efficiency and the service life of downhole tools, especially in ultra-deep or long distance horizontal wells.

In the process of long horizontal well in directional drilling, serious contact between drill string and wellbore leads to weight on bit loss. Therefore, this paper proposes a drill string rotary controller (DSC) for directional well, and its function test is completed through the experimental platform. Connected DSC working mechanism, a drill string coupling dynamic model is established under conditions of horizontal well in directional drilling. In the case study, the coupling dynamic characteristics of different units, including drill pipes and bottom-of-hole modules in axial and torsional directions, are studied. The results show that the effective value of drilling rate increases while the axial vibration velocity and amplitude of drill bit decreases. Moreover, in torsional direction, when drill string system is stable state, the rotating angular velocity of different drill pipes, rotary table, and collar is 31.16 rad/s, and the angular velocity of drill bit is 43.19 rad/s, respectively. It indicates the DSC working performance, which enhances the drilling system balance capacity. Overall, different from the sliding friction between wellbore and drill string, the addition of DSC realizes the separation and meshing of drill string and bottom hole modules, which can significantly increase the transition efficiency of weight on bit and torque value. Theoretical and experimental researches prove that the tool can effectively solve the problem of serious weight on bit loss in directional drilling process, and provides a new reference and idea for developing directional drilling technology when facing new challenges.

Summary: A high-frequency axial-torsional composite percussion drilling tool is designed to enhance the drilling efficiency by delivering high-frequency axial and torsional impact loads directly to the drill bit. The impact performance and influencing factors of the tool are analyzed via the large eddy simulation method, and a scaled-down experiment on the pulse nozzle structure is conducted. The analysis reveals that after design optimization, the tool achieves high-frequency axial and torsional impacts of 421 and 284 Hz, respectively, at an inlet flow rate of 30 kg/s. Additionally, the unilateral amplitudes of the axial and torsional impact loads reach 1511 N and 19.3 N·m, respectively, with a pressure drop of 2.998 MPa. Furthermore, the similarity degree between the parameters derived from the experiment and numerical analysis is close to or exceeds 70%, demonstrating the reliability and precision of the numerical analysis results. Overall, this study sets a baseline for high-frequency impact technology, paving the way for further advancements in drilling efficiency.