Research On The Structure Of MWD Rotary Valve Pressure Continuous Wave Generator And The Rotor Force Analysis

Measure while drilling (MWD) is a kind of modern drilling supporting technology, which can real-time measure and transmit the downhole information during the drilling process. MWD usually transmits the downhole data by the drilling fluid information telemetry system, in which drilling fluid pressure wave generator is the core device. To improve the information transmission rate, the current advanced drilling fluid information telemetry system transmits the downhole data by the continuous pressure wave generator, which is based on rotary valve or oscillating shear valve, and transmits downhole data in a bandwide mode. This paper conducts the theoretical investigation on the generation mechanism of drilling fluid pressure wave, the design of the rotary valve and the force condition of the rotary valve rotor, etc, aims to provide theoretical guidance for the development of the continuous pressure wave generator.According to the non-steady flow water hammer theory of hydromechanics, a mathematical model of drilling fluid pressure wave is built by study of the pressure wave generating mechanism. Combining the characteristics of rotary valve, the mathematical model of sinusoidal pressure wave is built, and the theoretical relationship between the valve hole opening extent and the pressure amplitude is studied. According to the process analysis and the structural characteristics of a four-valve holes rotary valve producing the water hammer pressure, the structure and geometric parameter of the rotary valve stator and valve hole of rotor are determined by mathematical modeling and calculation respectively based on the establishment of surface micro-element in the condition of not considering the mechanical motion characteristics of the rotor. Those can provide a theoretical basis for the valve hole parameters design for the rotary valve rotor generates the sinusoidal pressure under the minimum force condition.According to related theories of engineering hydromechanics and mathematical model of drilling fluid pressure wave, combining with the axial force analysis on rotary valve rotor, the rotary resistive torque of rotor under the effect of water hammer pressure and the throttle resistance of valve hole is analyzed. Numerical calculations show that the axial force on the rotor is mainly generated by the throttle resistance of valve hole, and it linearly changes with the valve hole opening. When the valve hole almost all shuts down, this force will have a considerable load and rotor rotary resistive torque on the rotor thrust bearing. Through the axial force analysis of the rotor, it will provide theoretical basis for the determination of the thrust bearing parameters and the drive and control method of the rotor in the case of variable resistive torque.