An Experimental Study Of Friction And Torque Of Drilling Strings In Three-dimensional Bent Wellbores

With the development of horizontal wells and directional wells,the friction and torque of drilling string is one of obstacles for the well.For the moment,there are many methods to solve friction and torque,but there is big difference among them,and all of them have not been certified by experiments.So it is very important that select a well-adopted and high accuracy method.The paper designed and built an experimental facility for drilling strings mechanics in three-dimensional bent wellbores,and had a study for the friction and torque of drilling strings.The experimental facility could change the parameter of simulative wellbores,include radius of curvature and torsion angle.It could simulate drilling strings with stabilizer or not.Also it could simulate tripped in,tripped out,boring by rotation etc.operational mode.The results showed that: the friction of drilling strings in three-dimensional bent wellbores was relative constant with small fluctuation;the torque was cyclical fluctuated which the period was same to drilling strings rotation;among the factors that affect the friction and torque of drilling string,curvature had a positive correlation,as well as torsion angle;the stabilizer would enlarge friction and torque;the drilling strings had different friction and torque under operational mode,when tripped in or tripped out,the friction were roughly equal,but they were bigger than role in;when the drilling strings rotating from the bottom of hole the torque was bigger relative to rolled in;the comparison indicate that different method that be used for friction and torque have different accuracy: the results of soft model were much smaller than measured value,the friction from beam-column model was bigger than measured value when the torque was smaller than measured value,but the torque was roughly equal with the measured value when role in;the results of elastic rod model were roughly equal with the measured value under different operational mode;the results of soft model,beam-column model and elastic rod model tended to equal when decreed the stiffness of drilling strings or decrees the curvature of borehole;the experiment founded that there were two weakness spots that near the telos of in three-dimensional bent wellbores on the drilling strings,which provided preference for drilling strings design,select or strength check.