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.

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.

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.

During well testing and production, the helical buckling often occurs near the lower end of tubing and friction appears. When loading continues or temperature increases, the tubing deformation will develop under post buckling condition, and it is difficult to describe the axial force with analytic method, that is why numerical method is needed. In this paper, plastic incremental theory in plastic mechanics is used to calculate the axial force distribution of buckled tubing strings, according to which the final axial force and deformation are determined by both the initial state and the loading process. It is found that the axial force distribution of tubing with friction is changed significantly and is strongly dependent upon the operation steps. The friction can prevent the large loads caused by high pressure and/or high temperature from spreading so that only a small part of tubing deforms severely. This calculation method was verified by experiments and has been used in oil fields.