CONTACT-IMPACT DYNAMIC SIMULATION OF DRILLSTRING AND FORMATION BASED ON LAGRANGIAL ELEMEMT METHOD

In the most causations affecting drilling transverse vibration,contact-impact of drillstring and formation was the most important.Based on the continuous mechanics and nonlinear finite element method, several control equations about contact-impact of drillstring and formation were established, and the dynamic finite element formulations and discretionary for contact-impact of drillstring and formation were given. The contact-impact dynamic equations based on lagrangial method were solved using explicit integration. The numerical results of the contact-impact can reflect the dynamic process of contact-impact really and agree with the prevenient experiment well. The results show that: in the condition of this article the first principal stress of the drillstring can reach to 308 MPa, the result is beyond the normal estimate; contact-impact is the principal surce of drill premature failure; this method is useful and suitable for the future drillstring dynamic research. Using explicit integration and nonlinear finite element can simulate the collision between the drillstring and formation successfully, the process of the collision between the drllstring and formation can be revealed compressively and delicately.