Structural Design And Optimization Of Mud Pulse Generator

In the process of drilling,with the increase of drilling depth,drilling difficulty increases,LWD parameters increasing,real-time data transmission more urgent and imminent development of signal transmission rate higher.In this paper,the types,advantages and disadvantages of parameter transmission are analyzed.It is pointed out that the speed of data transmission is the fastest,which is the research direction of this paper.Firstly,In this paper,the working mechanism of mud pulse generator is explained by the principle of thin wall orifice throttling,and the influencing factors of mud pulse attenuation are introduced,which paves the way for the design and optimization of the mud pulse generator.The working principle of the mud pulse generator is numerically analyzed by using the principle of thin wall orifice throttling.It is found that the pressure difference ΔP is only related to the flow area of the rotary valve when the flow and density of the drilling fluid are constant.Therefore,when the stator,rotor structure of the valve design reasonable,control the rotary valve flow area of change,then can get continuous pressure wave signals.And the 3D model of the mud pulse generator is drawn by Slidworks.Secondly,a mud pulse generator is designed,which is a continuous wave mud pulse generator,which is compact,simple,reliable,and has high transmission rate.The mud pulse generator mainly consists of four parts: the valve mechanism,the drive mechanism,the generator assembly,the shell,and some protective sealing parts.The rotary valve mechanism is the most critical component of the mud pulse generator.The previous chapters of this paper have been designed and optimized in detail.The drive mechanism mainly includes: transmission shaft,planetary gear reducer,brushless DC motor,pressure compensation structure,wire protection structure and sealing support structure.As the power source of mud pulse generator,the generator assembly is very important for the design.It is designed as a turbine generator and an electromagnetic coupling method for inputting mechanical energy.Also designed the corresponding seal and support structure,to ensure that the mud pulse generator normal work.Then,a novel method is proposed.According to the principle of thin-walled orifice throttling,the mathematical model of the shape of the valve port and the pressure of the mud pulse is established by the relationship between the pressure difference generated by rotating valve and the fluid flow area.According to the relationships between the fluid differential pressure of a thin-walled cutting edge and the fluid flow area and between the correlation coefficient of the theoretical pressure difference and the standard sinusoidal signal,an improved arc-fillet-line triangular valve orifice is designed to output highly similar sine pressure signals.Finally,the orthogonal experiment is used to further optimize the parameters of the mud pulse occurrence mechanism,and the optimization scheme is designed.The scheme includes three factors(the distance between stator and rotor d,rotor thickness h and rotor speed r),four levels and two indicators(peak pressure peak H and hydraulic torque N),a total of 16 groups of experiments.Then the CFD software is used to simulate the flow field of the mud pulse generator rotary valve structure,and 16 sets of structural parameters are set up to simulate the transient pressure of the upper surface and the lower surface of the rotor and the hydraulic torque of the rotor N.Using the method of orthogonal experiment to analyze the simulation results,and the influence of various factors on the pulse signal is obtained and the best optimization structure is concluded.