Analysis On Dynamic Stress Of BHA In Strapdown Rotary Steering Drilling

Due to the existence of the guiding force,the bottom drilling assembly in rotary steering drilling is more complicated,and the risk of drilling tool damage increases.On the basis of the research achievements of the dynamic mechanics of drill string,a dynamic model of bottom hole assembly in strapdown rotary steerable drilling is established.By using the ABAQUS software,starting from the initial configuration of the drill string,loading drilling pressure,torque,thrust force,contact force,damping force of load distribution,real-time detection and changing the boundary conditions,a method for calculating dynamic stress of drill string is established.Ignoring the specific structure of drill string combination,the peak value of dynamic stress increases with the increase of drilling pressure;When the speed increases,the stress change cycle changes accordingly,and the peak value of stress increases with the increase of speed;When the length of drill string changes,the stress wave cycle is almost constant,and the stress peak value changes little.The dynamic calculation of bottom hole assembly of strapdown rotary steerable drilling shows that the maximum equivalent stress of BHA is at the bottom of drilling tool;The drilling pressure increases,the average stress level increases,the peak value of the dynamic stress increases,and the specific position of the peak stress point is different;When the speed increases,the dynamic stress peak value of the bottom hole assembly increases,and the stress peak point is different;Change the position of centralizer effect on dynamic stress is larger,centralizer and bit distance increase,dangerous stress position change,the peak stress increases obviously;Increase the number of centralizers,dynamic stress peak is not reduced.The natural frequencies of the transverse vibration of the BHA are densely distributed.It is difficult to completely avoid the critical speed of drill string,so drill string is prone to lateral resonance.In the vicinity of the natural frequency,the lateral vibration displacement response of BHA is very large,sometimes close to the common speed values,such as 34r/min and 92r/min.The local resonance occurs,the trajectory of each node of the drilling tool is more complex and dangerous stress position changes,and the peak stress increases by about 25MPa;When the drilling pressure increases,the stress fluctuation of the same node becomes larger;With the increase of local resonance frequency,the stress fluctuation frequency of the same node increases;When the speed increases,the stress amplitude of the same node increases,and the vibration of the drill string is more severe.The research work of this paper has certain guiding significance for the optimization of drilling assembly and operating parameters of strapdown steerable drilling.