Salt precipitation from the drying-out process has a profound effect on the well injectivity during the storage of carbon dioxide (CO2) in deep saline aquifers. Both gravity and reservoir heterogeneity have a significant impact on CO2-plume behavior and CO2 storage capacities. The collective effect of gravity and heterogeneity on the drying-out process by site-scale numerical simulation based on the Sleipner project had been investigated. Three site-scale permeability heterogeneous models and a fracture model had been built; simulation results showed that the gravity effect significantly increased the solid saturation at the injection well in the homogeneous model; changing the position of the injection well can change the distance that gravity can act and affect the amount of salt precipitation near the injection well. A novel conclusion is gravity and heterogeneity showed a mutual resistance relationship when considering the collective effect of gravity and heterogeneity on solid saturation. Gravity effects reduced the amount of salt deposited in the fracture model; at low CO2 injection rate, gravity force dominated CO2 flow; increased rock heterogeneity suppressed the production of salt precipitates; at high CO2 injection rate, viscous force dominated flow; and increased heterogeneity increased salt precipitation. This research is of important guiding significance for the design of site screening and injection schemes from the perspective of avoiding a large amount of salt precipitation and pressure build-up.
Shear displacement will lead to the change of rock fracture space and then affect seepage characteristics of the fracture, but for the same rock fracture, whether the spatial geometry and seepage characteristics of the fracture can be consistent under the forward and reverse shear displacements is a new question. In this paper, the 2D rough fracture profile was used to establish models of different shear displacements in the forward and reverse directions without contact zone, and the geometric distribution characteristics of the fracture space with shear displacements were analyzed. The FVM (finite volume method) was adopted to calculate and simulate the hydraulic characteristics of the relative seepage direction (forward and reverse flow) under different pressure gradients at various shear displacement models. The results showed that under the same shear displacement, the spatial geometry characteristics of forward and reverse shear displacements are consistent after the initial angle of the fracture profile is eliminated. The slope of equivalent hydraulic aperture decreases with the shear displacement, and the amplitude of the non-Darcy coefficient difference increases with the shear displacement, which are inconsistent in the forward and reverse directions, which are negatively correlated with the directional roughness of the initial fracture profile. It shows that the directional roughness inconsistency between the forward and reverse directions of fracture profile is the primary factor leading to the difference of seepage characteristic parameters under the forward and reverse shear displacements.
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