Dynamic Analysis Of Point-the-Bit Rotary Steerable Drill Multibody System

Rotary steerable drilling tool was a key tool to realize complex drilling technology and represents the highest level of drilling equipment development in the world today.Rotary steerable drilling tool and its steerable drilling system was a complex multi-rigid and flexible system.The dynamic analysis of rotary steerable drilling tool was one of the foundations to improve the stability and directivity of the steering drilling system.At present,the traditional dynamic analysis methods for rotary steerable drilling tools mainly include classical differential equation method,finite element method,energy method and computational multi-body system dynamic method.The above methods were computationally heavy and inefficient.However,since the transfer matrix method of multi-body system did not require the establishment of the system’s overall dynamic equation,and had a high degree of programming and computational efficiency,based on this,this paper applied the transfer matrix method of multi-body system to the dynamic analysis of the point-the-bit rotary steerable drilling tool,and the steady-state dynamic characteristics of point-the-bit rotary steerable tool,the transient dynamic characteristics of bottomhole assembly(BHA)with point-bit rotary steerable tool and its deflection performance were studied.The main contents were as follows:According to the basic idea of steady-state multi-body system transfer matrix method,the point-the-bit rotary steerable tool was equivalent to the typical components such as mass point,massless elastic beam,coupling bearing and support element,and the steady-state transfer matrix of the typical components was derived.Based on the comprehensive consideration of the interaction between the housing and the spindle,a dynamic model of the housing-bearing and spindle system of the point-the-bit rotary steerable tool was established.The first three natural frequencies and vibration modes of the steering tool under working conditions were obtained.The offset of the main shaft was calculated,and the correctness of the multi-body system dynamics model of the point-the-bit rotary steerable tool was verified by the experiment of the indoor rotary steering tool bench.Based on the basic principle of transient multi-body system transfer matrix method,the BHA was equivalent to three typical components: rigid body,flexible body and fixed hinge.The transient transfer matrix of typical components was derived.The transient multibody system transfer matrix method was used to obtain the lateral dynamic response of bottomhole assembly at different speeds,and the feasibility of the transient multibody system transfer matrix method to solve the dynamic response of bottomhole assembly was verified by comparing with the classical dynamic analysis method-finite element method.The dynamic model of point-the-bit BHA multi-body system was established by using transient multi-body system transfer matrix method.Combining the boundary conditions of point-the-bit BHA and the total transfer matrix of the system,the dynamic model of point-the-bit BHA multi-body system was solved,and the dynamic response of point-the-bit BHA was obtained.The influence of drilling parameters on torsional and lateral vibration characteristics of directional BHA was discussed.The recommended range of drilling parameters which can ensure the relative stability of point-the-bit BHA in space during rotary steerable drilling is given.In addition,the effects of rotational speed,weight on bit and bias force of bias mechanism on skew building performance of point-the-bit BHA were simulated respectively.The results show that under fluctuating weight on bit,the bit angle and lateral force show a sinusoidal fluctuation trend.With the increase of rotational speed,the bit angle and lateral force fluctuation period decreases,the frequency increases and the amplitude changes were small.With the increase of weight on bit,bit angle and lateral force fluctuation amplitude change little.With the increase of the bias force of the bias mechanism,the angle of the bit and the amplitude of the lateral force increase,as well as the fluctuation amplitude.