Soret-Induced Convection in a Layered Porous Medium Simulating an Anticlinal Geological Fold Under the Action of a Geothermal Temperature Gradient

The paper is devoted to the investigation of three-dimensional Soret-induced convection in a three-layer porous system imitating an anticlinal geological fold, under the influence of a geothermal temperature gradient. The layer porosities are the same and the permeabilities are different. The mixture of tetralin and dodecane is considered as a fluid saturating the porous medium. First, we study the linear stability of the motionless state of a binary mixture in an inclined porous layer under the vertical temperature gradient. It is found that at any layer inclination angle, the most dangerous disturbances are longitudinal rolls with finite wave numbers in perpendicular direction. With the system parameters under consideration, the presence of an impurity can change the convection threshold in both directions depending on the layer inclination angle. The threshold change can reach 26%. Nonlinear calculations are performed for fixed permeabilities of the external layers, lower than the threshold value according to the linear theory. Calculations have shown that after a long period of time from the beginning of the process (about 500 years or more for lower permeabilities), a flow arises. The development of a steady flow occurs over a long period of up to 6000 years. It is found that at small permeabilities of all layers, arising flow has a longwave character. With the increase of permeability of the middle layer (higher than $K_2=2·{10}^{-13}{m}^2$), the flow in the plane of a geological fold limbs takes the form of longitudinal rolls and in the perpendicular direction the flow structure becomes multicellular, this flow structure well corresponds to the linear stability results. The flow is localized in the middle layer and significantly influences the concentration field.