Among the many advantages provided by a horizontal well, it permits better knowledge of the reservoir, as well as implies an increase in productivity. The main objective is to drill reliably, safely and economically. To accomplish this, it is essential not to compromise the wellbore stability, which typically requires an increase in the mud weight. This workprovides a method to design the weight of the drilling mud to hold the fluid pressure, avoid collapse and breakdown of the formation. A knowledge of the formation breakdown pressure is also necessary in production operations such as hydraulic fracturing, secondary recovery, squeeze cementing or matrix acidizing.

This work reports the study of rockmass behavior resulting from underground excavation and injection of fluids by applying finite element simulation methods and rock mechanics, to simulate the wellbore stability and onset to hydraulic fracturing for horizontal wells. The stress redistribution analysis simulates three individual effects: the wellbore (hoop stress) effect, the internal pressure effect and the fluid flow effect. Nonlinear material behavior is described by the Mohr-Coulomb yield criterion. A number of examples are presented regarding the wellbore stability of a horizontal well considering fluid injection, the nature of the injected fluid, nature of the rock and orientation of the wellbore with respect to the least initial stress and impermeable barriers.

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