Conventional directional drilling mainly relies on the sliding of screw motor and drill string to realize the change of wellbore trajectory, so the friction force is large. The use of friction reduction tools that generate axial force to change the friction state can only achieve partial friction reduction, and drill string is still in a sliding state during directional drilling. These problems are solved by using rotary steerable drilling system, which can achieve directional drilling when drill string rotates. But its use cost is high. Considering the principle of high efficiency and economy, a new friction reduction tool called drill string rotation controller is proposed, which is also used to reduce friction during directional drilling through drill string rotation. By adjusting the pump pressure, the meshing state of spline module of drill string rotation controller is changed to realize the conversion of drilling mode. In rotary drilling mode, upper drill string, drill string rotation controller and bottom hole assembly rotate together. In directional drilling mode, upper drill string rotates and drill string rotation controller slides with bottom hole assembly. The function of the tool is verified by field experiment, and motion simulation of the tool is carried out. The results show that when the driving torque is set to 25000 N·m, more reverse torque can be overcome in the directional drilling mode, and the drilling fluid pressure is set to 25 MPa, which can be converted to the rotary drilling mode faster.
Aiming at the problem of low drilling efficiency of oil and gas wells due to the high friction during the drilling, a dual-piston axial oscillation drag reduction tool (DAOT) is proposed to reduce friction for long drill string in this paper. Based on the ground experiment conditions, pressure drop, axial displacement and acceleration of DAOT were tested with different input parameters. The pressure drop calculation model was established by fluid mechanisms applied, and the axial excitation displacement model to the damped elastic rod subjected to axial external excitation was deduced. Further, combining with the same parameters as the experiment and field application, the dynamic characteristics are studied by numerical calculation methods to identify proposed models. The results show that the correctness of the models is verified, the working pressure drop, axial displacement, working frequency and axial oscillating force are all dependent on the input flow, the working frequency is positively correlated with the input flow, and the more the input flow rate, the great is its influence on the oscillating force. The application of DOAT can reduce extremely the friction force of drill string and improve availably the drilling efficiency. These conclusions can be of benefit for optimizing multi-piston axial oscillating tool and DAOT field applications.
Internal motion and dynamics mechanism studies of a new composite percussion drilling tool aim at reducing stick-slip phenomenon and improving rock breaking efficiency. In this study, experiments are performed using composite percussion drilling tools to investigate its torsional and axial composite impact performance. According to the experimental results, a six-degrees-of-freedom (6DOF) rigid body motion model was established to study the passive motion of a torsional hammer. The obtained results, including the tangential acceleration, were verified with experimental data, and the small pressure differences between the high and low pressure areas, which mainly determined by the inlet structure, is the main reason for the poor torsional impact effects. Based on these discoveries, the improved design increases the inlet flow to 17.2% of the total, the pressure differences to 0.05 MPa, and the instantaneous tangential acceleration to 0.198 m/s2, which results in increased tangential acceleration fluctuation amplitude by 1137.5% and greatly improved torsional impact performance. This research can provide a baseline for stick-slip reduction technology optimization.
In the process of long horizontal directional well drilling, the contact between drill string and borehole wall leads to serious dragging pressure. Therefore, a Drill String Rotary Controller(DSC) for directional well is proposed, and the function test and performance test of DSC are completed through experimental platform. According to working characteristics of DSC, a coupled drill string dynamic model for directional well drilling is established. The coupling dynamic characteristics of different drill pipe sections and different modules in the axial and torsional directions are studied. The results show that in the process of directional drilling, the axial velocity of the bottom hole module is low. Under the action of formation reaction force, the drilling volume of the drill bit decreases, but it still keeps in contact with the rock. At this time, the drill string system is in a normal drilling state. When drill string is stable, the angular velocity of different drill pipes, rotary table and collars are stable at 31.16 rad / s, and the angular velocity of DSC and BHA are stable at 43.19 rad/s. It indicates the DSC works well, the drill string is balanced in the torsional direction, and there is dynamic friction between the drill pipe and the drill string, which is conducive to lower the drill string. Through theoretical and experimental research, the tool effectively solves the problem of serious drag pressure in directional drilling process, and provides a theoretical basis for directional well drilling speed increase.
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