Numerical simulations for wellbore stability and integrity for drilling and completions

Conventional wellbore trajectory planning is commonly based on an Andersonian state of stress [SoS] and the optimum well azimuth and inclination for a specific depth can be determined using stereographic projections of the safe mud weight window. In this thesis a new methodology using the complete stress tensor is developed to determine optimal well trajectories for complex in-situ stress scenarios. This study uses a 3D finite element analysis to simulate the SoS based on an integrated 3D MEM. The model yields the complete stress tensor at every location for a planned future well path. Using standard equations to determine the wellbore SoS for inclined wellbores the safe operational pressure window can be determined.;Included is a wellbore integrity study on the cement sheath of a well proposed for CO2 sequestration. This includes both the mechanical interactions of the casing, cement, and formation as well as the effects of temperature change which would be caused by CO2 injection. The use of a staged finite element model to accurately predict the pre-cementing wellbore SoS is proposed. The SoS results are then implemented into a wellbore model with a perfectly bonded cement sheath in order to investigate the effects of cement curing and degradation.;In this study the evolution of Young's Modulus during cement curing, and de-evolution during cement degradation is accounted for. Traditional cement integrity studies use only a constant value for Young's Modulus. The finite element models show that inclusion of cement hardening may increase the risk of shear failure in the cement, while inclusion of cement degradation may lead to tensile failure during cold CO2 injection.