46th U.S. Rock Mechanics/Geomechanics Symposium,
2012. American Rock Mechanics Association
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In this study we use three-dimensional Finite Element Analysis to determine the influence of specific geometrical relationships on the feasibility of CO2 injection into anticline reservoir settings under different in situ stress regimes. Anticline structures as an example of folded sedimentary layers are among the most common structural traps for hydrocarbon reservoirs and thus become a prime target of the emerging challenge of safe geologic sequestration of CO2. This study shows how stress field heterogeneities within generic anticline structures affect geomechanical risks associated to CO2 injection. The method used to assess the geomechanical risk is the calculation of the critical pore pressure increase that the reservoir can withstand without the reactivation of existing fractures or the formation of new second-order fractures. The specific characteristics evaluated in this study include the relative thickness of the reservoir layer, the amplitude of the anticline and the wavelength of the anticline. Our results show that anticline structures exhibit a highly heterogeneous state of stress, and the geometrical parameters of wavelength and amplitude contribute to the stress heterogeneity. The results further show that the critical sustainable pore pressure also varies with respect to horizontal location in the structure. The most significant factor controlling stress heterogeneity in the anticline structures is the prevailing stress regime. Compared to horizontally layered basin models our results suggest that for extensional and strike-slip regimes anticline structures provide safer conditions than horizontally layered basins. This study shows that in order to realistically assess geomechanical risks associated with CO2 sequestration, three-dimensional models which realistically resemble the reservoir structures are necessary. Models based on horizontally layered basins represent an oversimplification and do not account for mechanical contributions, which are associated with the geometry of the structure, when geomechanical risks are analyzed.
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