Dynamic characteristics of bottom hole assembly in Bozhong 19-6 structure

During deep-well drilling in Bozhong 19-6 structure, complicated situations of torque increasing and hanging load decreasing appeared when Ø406.4 mm borehole drilled to the depth of 2 841 m by using the bottom hole assembly (BHA) of PDC and power V.After it was pulled out of the hole, the connection between the piston sleeve and the straight shell of the motor was found to be fractured, which seriously wasted drilling time and cost.In order to reveal local stress distribution of BHA, a three-dimensional finite element model of BHA-bit-formation was established on the basis of ABAQUS software.Then, based on the parameters of actual downhole working condition, the model was solved by means of explicit time integration method.Finally, the stress applied on BHA was analyzed.It is shown that there is a stress concentration point on the motor, and stress appears periodically and repeatedly over the time, which conforms to the characteristics of fatigue failure.Furthermore, the concentration point basically coincides with the fracturing location, which verifies the accuracy of the model.The model is of some guiding significance to the dynamic analysis on the BHA of deep wells in Bozhong structure.