Thermoporoelastic wellbore stability model with local thermal non-equilibrium

Wellbore stability is a key challenge for the exploration and production industry since it adds a great deal of additional cost. Traditional wellbore stability models such as elastic and poroelastic models are not sufficient in modeling the stability and produce erroneous results since they consider an isothermal condition. The industry also overlooks the potential impact of thermal effects on wellbore stability and utilizes a trivial approach in modeling the thermal stresses. During the drilling phase, the drilling fluid temperature is different from the formation temperature due to geothermal gradient and circulation of the mud inside the wellbore. Therefore, the assumption of an isothermal condition will not predict the correct wellbore stability condition, especially for high pressure and high temperature wells. The knowledge of in-situ stresses, breakout, and breakdown is vital to oil and gas industry, affecting wellbore stability, well location, production rate, completion and casing designs. Determination of breakout pressure helps avoid wellbore enlargement and shear failure, while, breakdown pressure aids in knowledge of the formation fracture gradient and the limits for the drilling mud weight window. Estimations of breakout and breakdown gradients can substantially be affected by the induced thermal stresses that occur during the drilling phase of a wellbore. The fully coupled thermoporoelastic model developed in this dissertation reveals the importance of induced thermal stress in stress resolution and wellbore stability evaluation. It produces reasonable results compared to uncoupled models and models with isothermal assumption. Most existing thermoporoelastic models utilize the assumption of local thermal equilibrium. The local thermal equilibrium assumption ignores additional pore and thermal stresses in the porous medium caused by temperature variations of the fluid and solid phases. This dissertation investigates the effect of thermal stresses on stress resolution around a wellbore and wellbore stability in a fully coupled condition with consideration of local thermal non-equilibrium heat transfer. The model is applicable for any wellbore trajectories in low and high permeable formations with consideration of conductive and convective heat transfers