GEOMECHANICAL RISKS ASSOCIATED WITH CO2 SEQUESTRATION IN GENERIC RESERVOIR SETTINGS

In this study we use two-dimensional poro-elasto-plastic Finite Element Analysis to evaluate the geomechanical risks associated with CO₂ injection related pore pressure changes within several generic anticline reservoir settings. Subsurface reservoirs, such as depleted oil and gas reservoirs or saline aquifers, are prime candidates for the injection and storage of CO₂. Among the most common of these reservoir types are anticline structures. Anticlines have a nonlinear geometry resulting in a heterogeneous reservoir state of stress. The associated geomechanical risks not only depend on the increasing pore pressure but are a result of several key parameters such as anticline shape, relative reservoir thickness, existence of faults, coefficient of friction between layers, prevailing stress regime, injection rate and pore pressure. The geomechanical risks which are evaluated include reservoir and caprock stability, i.e. fracture generation and reactivation of preexisting faults and fractures. In detail, second order fracture likelihood, type, orientation and implications for fluid flow pathways are investigated. Our study demonstrates that in order to realistically evaluate geomechanical risk, an accurate representation of the reservoir geometry is necessary. Our initial results show that the maximum sustainable pore pressure, and therefore the maximum volume of CO₂ that can be injected without leakage, is dependent not on a single factor but rather on the interplay of many parameters within a specific reservoir. Specifically, the coefficient of friction between bedding surfaces significantly influences the state of stress and has direct consequences on second order fractures being generated.