Fully Coupled Thermo-Hydro-Mechanical Numerical Simulation of Geologic Storage of Carbon Dioxide in Layered and Folded Geologic Media

A series of numerical simulations using a fully coupled multiphase thermo-hydro-mechanical (THM) numerical model is performed to analyze groundwater and carbon dioxide flow, heat transport, and land deformation in geologic media due to carbon dioxide injection and to evaluate their thermo-hydro-mechanical stability for geologic storage of carbon dioxide. The geologic media are composed of a series of Jurassic sandstone aquifer (reservoir rock) and shale aquitard (cap rock) layers, which are layered and folded, over Precambrian metamorphic rocks at two oblique angles. Two different cases of boundaries between the sedimentary and metamorphic rocks are simulated to evaluate effects of geologic structures on geologic storage of carbon dioxide. One is a pair of faults, and another is a pair of unconformities. Four different locations of carbon dioxide injection are also simulated to evaluate an optimal location of injection in each boundary case. The numerical simulation results show that the layered heterogeneity and the geologic structures such as folds, faults, and unconformities have significant effects on the spatial distributions and temporal changes of groundwater pressure and saturation, carbon dioxide pressure and saturation, geothermal temperature, and land displacement vector. The free phase carbon dioxide (structural trapping), which is injected into sandstone, moves upward along the interfaces between the sandstones and shales and then accumulates under the anticlines. Over a long period of time, the free phase carbon dioxide (residual trapping) and the carbon dioxide dissolved in groundwater (solubility trapping) also move along the groundwater flow direction and then leak to the ground surface through the faults and unconformities. In case of the fault boundaries, such leakage becomes more accelerated and intensified. On the other hand, land deformation with ground surface uplift occurs during the injection period, and then the ground surface recovers to its initial state in accordance with the recovery of groundwater pressure after the injection period. Therefore it may be concluded that the layered heterogeneity and the geologic structures such as folds, faults, and unconformities cannot always be ignored if they are observed in actual geologic systems, and thus they must be properly characterized and considered when more rigorous and reasonable predictions of both long-term thermo-hydro-mechanical responses of the whole geologic systems to carbon dioxide injection and their storage stability are to be obtained. Further numerical studies of various geologic and hydrogeologic settings and field applications are recommended to arrive at more general conclusions concerning the effects of the layered heterogeneity and the geologic structures on multiphase fluid flow, heat transport, and land deformation due to carbon dioxide injection.