Mechanical Analysis Of Wellbore Stability Based On Rock Plastic Softening

The constitutive expression in stress space and strain space of mechanical properties of rock under moderate or low confining pressure was studied.A set of C++ programming was programed and debugged to analysis two cases of stability.The equilibrium path curve and stress and strain distribution of the elastoplastic softening stage around wellbore were obtained.This paper deduced constitution relation of elastoplastic deform of rock in stress and strain space,to get standard equation and the expression of numerical computation.The numerical computation method of finite element analysis was discussed,including the method of multiplied with bigger number,the calculation of stress increment,and the calculation of the projection on yield surface.Finite element method program was debugged and the transformation of stress and strain using the initial value was tested in experiment.Interface configuration of Visual C++,Visual C++ from Matlab engine and Patran for viewing results were studied with the process of programming and debug.The program had main program and subroutines with calculation of element node.Integral point,yield surface and mathematical calculation with iterative process and subroutines of Patran documents were also included.The results of the program showed the plastic softening around wellbore using equilibrium path curve.Abaqus finite element analysis was simulated and compared with the calculation of the program with better results.