Elasto - Plastic Mechanics Modeling And Finite Element Simulation Of Large Expansion Coefficient Expansion

The expandable tubular technology in new drilling technologies has achieved significant success in casing patch operation of casing damage well workover with small expansion ratio at about15%, while the development of expandable tubular with large expansion ratio at20-30%in the key technology of expandable tube-monobore well technologies and complex drilling technologies-has remained stagnant currently. Apart from the limitation of expandable tube materials, the establishment of proper elastic-plastic mechanical model in expansion with large expansion ratio and its corresponding design of expansion tool have become the key to research the expandable tubular technologies with large expansion rate.At present, most of the expandable tubular mechanical model employ the rigid-plastic mechanics model and simplified mises yield condition, and out of consideration for the stress increases after the yield point and the impact of casing local bending on swelling force during the expansion, resulting in larger error. Therefore, on the basis of power hardening mechanics model and the single curve assumption in this paper, the elastic-plastic mechanical model of solid expandable tubular in large expansion ratio has been built using the equivalent stress-strain curve, and the accuracy of the model has been verified through the comparison of expansion experiments and finite element simulation results.By using the elastic-plastic mechanical model of solid expandable tubular in large expansion ratio and finite element simulation results in this paper, the existing design of expansion cone has been improved effectively, the main conclusion gained are as follows:(1) When the expansion area of expansion cone is conical, the required expansion force is minimum, and the stress distribution is more uniform;(2) It is noted that the required expansion force is minimum, the equivalent stress in expansion cone surface is smaller and more uniformly distributed, and not vulnerable to scratches in the expansion when the chamfer radius of expansion zone transition section in expansion cone is Ro≤R≤R1;(3) By analyzing the expansion force functions and the finite element simulation of expandable tubular in expansion, it is shown that the optimal semi cone angle of expansion cone is mainly influenced by expansion ratio, while the other factors have less effects. The optimal semi cone angle is about12°～18when the expansion ratio is15%～30%. However, when the semi cone angle is too large, the tube bending is easier to wrap the expansion cone in the end of the expansion pipe which will result in higher difficulty for expanding;(4) Furthermore, the mechanics model and the finite element simulation in expansion show that if any one of them, t、f、φ, as the independent variable, the other parameters are fixed, the argument increases linearly with the hydraulic pressure, and shows a wide range; And the external diameter of expansion pipe decreases with the hydraulic pressure. Therefore, it’s very important to choose appropriate coefficient of friction, expansion ratio, and casing-wall thickness for reducing the construction difficulty of expandable pipe;(5) Through the analysis of the mechanical model, it indicates that the expansion casing pipe should select the tubing which have lower strength coefficient and higher hardening exponent, and as a result, the required load for expansion would be smaller. Moreover, the bigger work-hardening exponent of tube materials, the more uniform stress distribution in expansion, the higher forming limitation, and the better expanding performance.