CO2-Induced Creep on Draupne Shale and Impact on Cemented Wellbore Integrity Available to Purchase

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.

A challenge in carbon dioxide (CO₂) storage reservoirs is to identify and prevent leakage. Wells, used to inject CO₂, could risk becoming a leakage path if well integrity is lost. CO₂ threatens wellbore integrity when it diffuses into a formation through gaps or cracks in a cemented annulus. Dissolution of CO₂ in formation brine is a trigger of geochemical reactions because of the formation of carbonic acid, see Equation (1)

(equation) (1)

This reactive fluid acts on specific gradients in the formation rock, hence, affects the geomechanical response. The formation rock referred to in this study is shale, which occupies a large portion along the potential leakage path from the CO₂ reservoir to the surface.

A recent review paper by Bhuiyan et al., 2020 has concluded that the interactions between CO₂ and shales occur in different states and scales. Lab tests revealed that Young's modulus decreased when the shale samples were saturated in CO₂-brine for a longer time (Zhang et al. 2017; Lyu et al. 2018a, b). However, how the CO₂-brine affects Poisson's ratio was not well studied in the aforementioned works. As observed by Agofack et al., 2019 in a CO₂ injection test, Poisson's ratio shows a measurable reduction.