| Geological storage of CO2 in disused oil and gas reservoirs is perhaps the most promising technique to reduce CO2 emissions into the atmosphere because of the economic benefits that incremental oil recovery can bring in a tight energy market. However, the acceptance of this new paradigm will require a perception of geological storage as a safe and environmentally sound practice. Therefore, it is necessary to make CO 2 storage predictable to avoid any negative impacts to the environment or society and implement a carbon emissions market. In the short-term, or injection stages, the main trapping element is a competent caprock, and its performance is a vital component of the risk assessment of any CO2 storage project. Geomechanics plays a key role in the performance assessment of the caprock and the reservoir as the hydraulic integrity of this system must be ensured both during the exploitation and production stages (pre-CO 2 injection), and during CO2 injection in any CO2-EOR storage project. The IEA Weyburn CO2 Monitoring and Storage Project has offered a unique opportunity to conduct a geomechanical performance assessment of a caprock system overlying a large scale CO2-EOR storage project. New experimental facilities to evaluate the hydro-mechanical properties of caprocks at high pressures and high temperatures were built. In-situ stresses evolution and thermomechanical considerations were identified as the most relevant issues for any CO2-EOR storage project from a geomechanical perspective. In-situ stress measurements and downhole monitoring of pressure and temperature should become mandatory as part of the regulatory and/or operational process for these projects. These conclusions were achieved through the systematic use of performance assessment techniques that include scenario analysis, model development, and development of working criteria. Moreover, it was found that the Weyburn field is a safe and sound sink for CO2 storage as long as the CO2 injection does not cause the development of tensional thermal stresses in the caprock, and the injection pressure remains below the minimum horizontal stress. Finally a methodology to carry out geomechanical performance assessments in CO2-EOR storage projects and manage uncertainty was developed, which can be applied elsewhere. |
