Amir Ahamdi - University of Ppetroleum Engineering, Tehran Iran
M. R. Asef - Tarbiat Moallem University, Geology Dept, Tehran, Iran
M. Afshar - University of Ppetroleum Engineering, Tehran Iran

Hole problems (such as lost circulation, where tensile failure has occurred, and spalling and hole closure in case of compressive failure) during drilling are often the consequence of mechanical wellbore instability. This leads to loosing time, higher costs and in severe case loosing of hole. This paper focuses on stresses around the wellbore. However, there is no clear choice of which compressive failure criterion in the analysis. Therefore, we first review and define a number of failure criteria that are commonly used in rock mechanics. Then, verify the required formula for critical wellbore pressure and stability analysis. Finally, by means of a visual C++6 computer programming code, written for this research, we could compare the outputs based on different failure criteria, and appropriate decisions were made

Failure criteria, Stresses around borehole, Visual C++6