ABSTRACT
ABSTRACT: The key technological problem in working in claystone formations is that the nonlinear deformation of a wellbore can cause a sudden collapse of the wellbore. Because this problem, this paper discusses a large-scale physical true triaxial simulating apparatus for wellbore deformation based on the development of a wellbore deformation measuring apparatus and a real-time detecting experimental study of wellbore deformation that was carried out under different loading stresses. The results are that: (1) A wellbore assumes an elliptical shape under the effect of differential stress and a wellbore wall begins to peel off and then collapses along the direction of minimum stress while generating cracks along the direction of maximum stress. (2) Wellbore deformation contains several visible stages. A wellbore with a soft rock sample appears to peel off as the differential stress decreases along the direction of minimum stress, while the differential stress first increases and then rebounds quickly after a wellbore with a hard rock sample appears to peel off. (3) The wellbore deformation rate is affected by the loading rate. The deformation rate of soft claystone is higher than that of hard claystone. This experimental study and discussion are significant for the control theory of wellbore nonlinear failure in claystone formations.
