ABSTRACT
The stability of circular openings is a problem of many disciplines, including the geotechnical, mining and petroleum industries. Although circular openings have been studied extensively in mining and tunnelling, the application to the oil industry needs slight modifications because of particular unique characteristics.1 ,2 Deep boreholes suffer from severe instabilities and breakouts that in general lead to progressive deterioration of the borehole and may delay or even stop drilling. In recent years, there has been substantial industrial interest to pursue research in this area, since borehole deterioration or collapse usually results in capital losses of several million dollars. Wellbore breakouts are attributed to the existence of significant tectonic forces that act in the horizontal plane at great depth. It should be noticed, however, that not only the stress deviator, but also the temperature gradient and porefluid pressure gradient influence borehole stability. The analysis here focuses on stress-induced instabilities.
