Wellbore stability has been traditionally analyzed by comparing the stresses to the formation strength. In addition, most of the problems have occurred in the shales; hence, have been attributed to the chemical interaction between the drilling fluid and the rock. However, field evidences urge for (he development of an improved way to analyze the stability of oil wells, due to the increase in challenges resulting from considering more difficult reservoirs.

This paper presents an innovative way to analyze wellbore stability using energy concepts. The rock mechanics aspects are emphasized; laboratory experiments usually interpreted via a mechanistic way should actually be evaluated in a more comprehensive way with energy. By analyzing the failure process of rocks, wellbore instability is explained by (he creation of surface fractures, with subsequent mud penetration. The paper describes the most energetic phenomena during (he drilling of a well, with the corresponded effects on the stability.

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