A STUDY ON THE STABILITY OF TUBULARS IN INCLINED WELLBORES

Based on the theory of large spatial deflection of elastic rod, this paper sets up a differential equilibrium equation governing tubulars constrained in inclined wellbores in convected coordinate system. To compare the effects of end constraints of tubulars on its buckling behavior, two different models (a pin-pinned model and a pin-fixed model) of tubulars are employed. The differential equation is solved with series method. The residuals in space domain are eliminated by Galerkin method. The relationships between the dimensionless parameters of tubular structures and the wellbore geometry are presented graphically. The results show that the higher the wellbore inclination angle and the smaller the radial clearance, the larger the critical weight-on-bit to initiate tubular buckling. The bifurcation value curves have reference significance to some extent in predicting the buckling behavior of tabulars. As two different models give almost the same bifurcation values, it seems that the controlling factor in the buckling behavior of tubulars in inclined wellbores is the lateral constraint of the well wall, whereas the effect of different end conditions can be neglected.