The Analysis Of Tubular Column Sinusoidal And Helical Buckling In Vertical Wells With Slow Dynamic Method

In drilling, logging, fracturing, oil exploitation and other petroleum drilling engineering, will use a large number of tubes of various sizes. The buckling of the tubular column not only limits the transmission shaft power and torque, even make the tube "locked." Therefore, the buckling of the tubular column is particularly important.According to the post buckling shape and characteristics of vertical well, discrete tube into beam elements, simulate the contact between the tube and the borehole wall as beam elements inner contacting. Slow dynamic method is proposed to calculate the column buckling, with the thought of the transient dynamics method to solve statics problem, analysis application of the load, and selection strategy of damp and sub-steps. To study the plane sinusoidal buckling, the critical buckling pressure column length in good agreement with the analytical solution. The study of space string helical buckling, without considering the impact of the contact pressure and resist twisting individually or simultaneously, critical load finite element solution with the analytical error is less than 1%. Considering contact effects, pressure and torque affect alone, because of the discontinuous contact, the buckling section is in conflict with the continuous contact assumption, and the error of the analytical solution is a little large. However, if the pitch is in continuous contact segment in terms of error of less than 3%. The influencing factors of the spatial helical buckling of drill string in vertical well are analyzed. With the increase of the length of the drill pipe, drill collars of its impact on the buckling becomes gradually smaller. With the increase of drilling pressure, the length of the contact section and the spiral angle gradually become larger. When the drilling pressure and torque at the same time, the angle of the spiral angle of the drill string is only slightly increased compared with the single action of the drill pressure, but the length of the contact section and the effect of the drilling pressure is reduced by nearly 40% and the influence of friction coefficient on buckling is little. Install two or three centralizer, can better suppress the helical buckling of the drill string, rotational speed will increase the fluctuation of drilling pressure, it also increased buckling of the drill string, but its effect is less than the impact of drilling pressure. The research results of this paper can be used to calculate the buckling problem of downhole pipe string, which can provide reference for the analysis of sinusoidal and helical buckling of the twisted tube.