Deep Vertical Wells Drilled Column Idling Power And Buckling Theory

Using the knowledge of solid mechanics, hydrodynamics, and mathematics and so on and based on the works of the predecessors and the new research results, this thesis establishes the mathematics models for the power consuming of unload, cutting rock power and the buckling of drill string. This thesis presents an analytical model in a cylindrical coordinate system for the power consuming of the friction, which is caused by centripetal force of the drill string without weight on bit (WOB) while it rotates. The drilling mud in this model is assumed to be Newton fluid. Therefore, this model has a good accordance with the reality by synthetically considering the rotate angular velocity, the structure parameters of the drill string and the well, the viscous coefficient of drilling mud and etc. In a word, the centripetal forces of the drill string and the shearing strength caused by the fluid are considered in the model, which makes it have a better utility than those existing. The drill string in straight well will bend when the axis force on the drill string exceeds the critical force. First the drill string is sinusoid bending. When the axis force increases, the drill string will be helical buckling. Consequently, this paper investigates the relationship between the axis critical force under sinusoid or helical buckling and the maximum speed of drill string. According to the energy method, we first consider that the sinusoid or helical buckling energy of drill string equals the work of the eccentric force plus the work of the gravity and then obtain a mathematics model for the speed——axis critical force. Considering the inertial eccentric force and the weight of the drill string, we find that the axis critical force will be obviously less than that under the static state, which should be very important in drill engineering applications. The cutting rock power models used at home and abroad now mainly are experienced formulae which are obtained by tests. The models can not reflect the quantity relationship among the parameters. It is difficult to consider the values in the formulae related to many factors. So when we used them to calculate the cutting rock power, the results are approximations. But the model in the paper can reflect the factors affecting the cutting rock power using mechanical methods. The effect of the bit and rock anisotropy and the static and impacting axis force are analyzed. This paper presents an analytical model for the power consuming of cutting rock caused by tricone bit while rotating the drill string. The cutting force of the tricone bit and the friction between the bit and the rock are considered in the model, which makes it have a better utility than those existing. Seen from this model, the power consuming of cutting rock can be improved sharply by using the rational WOB, rotate angular velocity and the structure of the tricone bit. This should be very important in drill engineering applications.