The Instability of Wellbore & Its Trajectory (IWIT) is a key academic and technological problem in the course of drilling, which can exert serious and direct influences on the quality, schedule and benefit of a drilling project. As a result, the research on this subject has attracted a broad attention from the circle. This paper, stresses the significance of the innovation, and discusses in detail such problems as the deviation and control of wellbore trajectory, the instability and control of wellbore, as well as the evaluation method for the characteristics of the penetrated formations, on which relevant academic ideas are expatiated. Finally, this paper discusses the development trend of drilling technology and the kernel problems to be resolved.

对石油钻井中井眼轨迹控制问题进行了力学分析，给出了底部钻具组合三维受力和变形的控制方程，建立了钻头与正交各向异性地层相互作用模型，阐明了井眼轨迹预测和控制计算方法。

It is difficult to determine real helical configuration by the current energy method. This paper describes an analytical solution based on equilibrium method, which represents the real configuration of helically buckled tubular subjected to axial and torsion loading in horizontal wells. New results of axial changes, bending stress and contact force in tubular are derived from the solution.

Based on and rock-bit interaction model and the data from drilling and logging, an effective inversion method has been developed for evaluating anisotropy of the drilled formations. Application of this method in oil field not only save money and reduce the trouble, but also improve the evaluation accuracy of the formation anisotropy parameters.

Based on the non-linear differential equations of buckled pipes, the buckling behavior of pipes in different wellbores has been analyzed. The relation between the deflection of buckled pipe and the loads on it has been given, and the critical loads for sinusoidal and helical buckling within different wellbores subjected to axial and torsional loads have been determined. Therefore, the profile of load increase during the post-buckling process and the bending moments in the buckled pipe can be determined. In addition, the effects of down-hole packer as fixed end on the helical buckling behavior of pipes have been investigated. These results can be applied to the related engineering design and construction.