A new 3D wellbore-stability model includes thermal stresses and the flux of water and solutes into and out of shale formations. Mechanical stresses around a wellbore are coupled with changes in temperature and pore pressure. Radial and azimuthal variation in stress distribution and failure index are computed to check for wellbore failure. Model results show that a porc-pressure maximum or minimum can occur within the shale and can lead to wellbore failure sonic distance inside the shale. Pore pressures at different times and positions are investigated, and it is shown that critical mud weight is strongly time dependent.