A simulation study of injected CO₂ migration in the faulted reservoir
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The injection and underground storage of carbon dioxide, CO₂, can reduce anthropogenic (human-generated) emissions of greenhouse gases into the atmosphere. Accordingly, the CO₂ sequestration into a deep saline aquifer is a subject of intensive study with current reservoir simulators incorporating dissolution, dispersion of CO₂ in water, and chemical reactions of CO₂ with existing phases and host rock. However, there is little information in the literature on the numerical analysis of the structural aspect of CO₂ sequestration. The purpose of this simulation study is to understand the effects of geomechanical structures, especially faults, on the behavior of injected CO₂ The GEM (Generalized Equation-of-State Model) Compositional Reservoir Simulator is used to observe how fault-related structure impacts behavior of injected CO₂ in the saline formation. Three main tasks are categorized as follows: 1) Comparison of the analytical approach for fluid distribution, based on Buckley-Leverett theory, with the simulation results; 2) Simulation study which illustrates the impact of fault properties on the behavior of carbon dioxide phase in a CO₂ and a H₂O (brine) saturated reservoir; 3) Simulation study which shows the effect of leakage through the fault (due to geologic imperfections) during the CO₂ migration These fault-scale interactions can play an important role in determining CO₂ and storage depending on whether the faults act as barriers, conduits or combined barrier-conduits. The simulator outputs reveal that each property of the fault as a barrier and also a conduit can restrict the migration of CO₂ through the reservoir as a consequence of compartmentalization (barrier) and bypassing (conduit). This study concludes that the properties of a fault and the interactions between the fault and the reservoir matrix can play a critical role in quantifying the behavior of CO₂ after injection ends. A fault within the target formation can have a positive or negative effect on the capture of the buoyancy-driven CO₂ with residual trapping mechanism depending on its geometry and/or petrophysical property. Accordingly, when it comes to the injection and storage of CO₂, an accurate prediction of the fault conductivity and petrophysical properties of the reservoir would be required to optimize the rate of injection and the storage capacity of the reservoir for the permanent capture of CO2.