Mechanics Analysis Of No-Open-Cut Directional Drilling BHA

In consideration of the problems of complex stress situation, difficult mechanics analysis and lack of theoretical basis of construction parameters of no-open-cut directional drilling BHA.The mechanical characteristics of no-open-cut directional drilling BHA were analyzed. The main research contents were included in the six aspects as follows:(1) The structure of well, BHA, environments, mechanics parameters and process parameters were all considered, and the mechanical analysis model of directional drilling and complete pipeline in the three cases of drilling guide hole, expanding hole and pulling back complete pipeline were finished.(2) The differential equations of the instability deformation of drilling string were established. The buckling of the drilling string and the ultimate load of the drilling string of buckling instability were analyzed. Therefore, the analysis formula of the external loads of the drilling string axial force and the well contact force were deduced.(3) The space deformation curves of tubular string were fitted by spline function, and the deformation curve of suspending tubular string were deduced by the method of weighted residual. By this way to analyze the stress and deformation of tubular string, it provided the basis to confirm the position for stabilizer.(4) The stress and deformation of horizontal tubular string were analyzed by elastic foundation beam method. In addition, considering the phenomena of support and sedimentation, the point of contact of suspending tubular string and well were analyzed.(5) The position of contact tubular string was analyzed with the consideration of the excursion of axes.(6) The loads, stresses and flexibilities in any position were analyzed in the three cases of drilling guide hole, expanding hole and pulling back complete pipelineBased on the analysis of the six aspects, the weakness positions of tubular string, the reasons of invalidation of horizontal drilling string, the choices rule of wheel stabilizer and tie-in were illustrated; also the safety of the two-criteria approach analyzing the horizontal drilling string was proposed.