Naser Samani
Hamed Daneshkhah

Borehole instability, in most of the cases, is a direct reflection of earth’s in situ stress state. It is well known that the stress distribution around the wellbore induces deformation depending on many factors ranging from wellbore pressure history and rock strength to the trajectory orientation. In situ stress direction have strong impact in drilling high angle wells. Proper placement of well trajectory with respect to in situ stress reduces instability in drilling. The paper exhibits example directional sensitivity of well trajectory in different in situ stress state and underbalance drilling condition and collapse pressure in all situation calculated by using Mogi-Coulomb criterion using an excel program.

Wellbore instability, in situ stress state, underbalance drilling, Mogi-Coulomb criterion, poroelastic