Wellbore leakage estimation with consideration of formation creep

A challenge in CO₂ storage reservoir is how to identify and prevent leakage. The wellbore, used to inject CO₂, could become a leakage path, for example, through the cement-rock interface. The influence of CO₂ on Draupne shale was investigated first. Shale samples were exposed to CO₂ saturated brine up to one week. The measured elastic moduli show a decreasing trend versus time. This time-dependent modulus was implemented in a user-defined model built into FLAC3D. The features of this model were first tested with a simple geometry. Then wellbore geometry was introduced to study leakage through the cement-rock interface. It was found that with a constant in-situ stress and different annulus pressures (before cementing), the cemented annulus behaved in different manner. The worst scenario could lead the cement-rock interface open and the wellbore lost the integrity.