| With the gradual depletion of oil resources,a wave of shale gas mining had been launched around the world,and based on the experience of domestic and foreign researchers and experts in the exploration and development of shale gas resources,it had been shown that horizontal well drilling technology was a key technology for the successful development of shale gas reservoirs,and in the horizontal section 1500~2000m of shale gas horizontal wells for the coiled tubing operation,because of the increase of friction for the coiled tubing,axial load increase was easy to produce sinusoidal buckling and helical buckling and self-locking,resulted in coiled tubing could not reach the target depth,the key to solve the shale gas horizontal wells self-locking was to reduce the friction of the wellbore.In this paper,a Φ73 axial hydraulic oscillator was designed for the pressure and selflocking problems in the drilling of shale gas horizontal wells,which consisted of two parts: the axial vibration short section and the hydraulic oscillation short section,and the power of the hydraulic oscillator was provided by the drilling fluid.First,the drilling fluid which entered the hydraulic oscillation short section through the center hole of the axial vibration short section,then a high-speed jet was formed after the nozzle of the jet element,and the high-speed jet controlled and drove the piston to do reciprocating movement in the cylinder by switching the wall inside the jet element.At the same time,the straight rotary actuator connected with the bottom of the piston rod made the rotating sleeve above the throttle hole do the reciprocating oscillating motion,periodically changed the overcurrent section area of the throttle hole,and caused the periodic pulse pressure wave at the entrance of the oscillation short section.When the pressure raised,the fluid pressure action axial vibration short section,forced the core axis compression disc spring group to move to the left,the core axis extended,when the pressure was reduced,the compressed disc spring group released energy,pushed the core axis moving to the right.In this way,the short section of hydraulic oscillation provided the power of the axial vibration section,which could drive the reciprocating motion of the coiled tubing and solve the pressure problems in the sliding drilling.It was found that the distance of vibration propagation in borehole was directly proportional to the working amplitude of the vibration friction reduction tool,so in this paper in order to achieve better solution to the pressure problem,the axial vibration short section and hydraulic oscillation short section of hydraulic oscillator were designed could form resonance to increase its working amplitude.In this paper,not only a large number of data collection and reading analysis were carried out for vibration and friction reduction,but also the research methods and design methods of vibration and friction reduction tools at home and abroad were studied,and the purpose and significance of designing axial hydraulic oscillators for small diameter coiled tubing were put forward.Then,combined with the research and development experience of vibration and friction reduction tools at home and abroad,analyzed and compared the working principle and advantages and disadvantages of several vibration friction reduction tools,determined the structure of the hydraulic oscillator which was designed with innovation,then introduced its working principle and studied the innovative evolution process of hydraulic oscillator,in the course of the research,the vibration principle and the beneficial principle of variable damage and the principle of prior precaution and the principle of mechanical substitution were used to improve the vibration performance and complete the structure of the Φ73 axial hydraulic oscillator.Next,the mechanism of the wall attached for the jet element was introduced,and its structure size was designed,and the flow field of the jet element in the hydraulic oscillation short section was simply deduced based on the knowledge of fluid mechanics,then the flow area model of the piston cylinder block of the jet element in the short section of hydraulic oscillator oscillation was established by using SolidWorks three-dimensional drawing software and hypermesh grid partitioning software,the flow field of the jet element and the flow field of the dynamic wall switching of the jet element were numerically simulated by using the fluent dynamic mesh technology,and the relationship between the flow rate of each channel under different incident flow conditions was simulated and analyzed,and chosen the appropriate incident flow that not only made the jet element can switch the wall,but also reduced the difficulty of its switching,and simulated the excitation frequency of the hydraulic oscillator oscillation short section which was 7 Hz under the given conditions.Then based on the previously obtained excitation frequency of the oscillation short section,combined with the knowledge of vibration dynamics,the vibration mathematical mechanics model of the hydraulic oscillator vibration short section was established,and the structure of the vibration short section of the hydraulic oscillator and the inner disc spring-core axis were designed,and the natural frequency of the vibration system of the disc spring-core shaft was similar to the excitation frequency of the oscillation short section,the natural frequency was 7.2 Hz,which enabled the vibration short section of the hydraulic oscillator to form resonance to increase the vibration amplitude.Finally,the water hammer was simulated for the different pore size of the direct rotary actuator in the short section of the hydraulic oscillator oscillation,and it was found that the water hammer pressure increased with the decrease of the radius of the runner port.These studies and simulations had improved the vibration performance of Φ73 axial hydraulic oscillator and perfected and optimized the structure more comprehensively,and improved the ability to solve the pressure problems in the process of coiled tubing drilling of shale gas horizontal wells,which provided a certain basis for further study of Φ73 axial hydraulic oscillator in the future. |
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