CALCULATION OF ELASTOPLASTIC DEFORMATION OF WELLBORE IN SOFT MUDSTONE USING LAGRANGIAN METHOD

In this paper we presented a review on the current situation of mechanical stability of wellbore in mud-shale bed and for the first time introduced large deformation theory into the calculation of elastoplastic deformation of wellbore and adjacent rock.Using Lagrangian method, we analyzed the problem of borehole shrinkage in mud-shale bed. Lagrangian method could solve the problem of material nonlinearity and geometry nonlinearity.In this paper we analyzed the calculation model using Lagrangian method with commonly adapted Mohr-Coulomb strength criterion, and solved the problem of wellbore shrinkage, the displacement field and the plastic region distribution of the wellbore and its adjacent rock.