Study on Reliability of Drilling Tool Joint in Extended Reach Well Based on Drill String Dynamics
Based on the BHA and wellbore structure of extended reach wells in Chenghai,under the conditions of the same WOB,RPM,and flow rate,the dynamic load borne by BHA at differ-ent well depths was calculated.The result shows the mean value of axial load on MWD decreases and the mean value of torque load increases.The bending moment is directly related to the well-bore curvature,and the load amplitude increases with the increase of the well depth.MWD is used to verify the dogleg degree of the borehole and the bending moment load borne by the drill-ing tool,which proves the effectiveness of the dynamic calculation.From the dynamic calculation results,the load spectrum of two working conditions with a harsh environment was selected,and the limit load on the MWD tool joint was applied,and the static strength of the thread was ana-lyzed.The result shows that the maximum stress of the external thread is located at the root of the second tooth away from the shoulder surface,and the stress of the internal thread is mainly concentrated from the small end face to the first tooth surface of the thread.The Mises stress of the thread is lower than the material yield strength.Under the condition of alternating load,the fatigue safety factor of the joint thread is 1.1～1.2 after 1.0× 107 cycles,respectively.There is still some risk under the condition of complex and changeable downhole working conditions.
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