The onset and evolution of nonlinear convective regimes of binary mixtures in multilayer systems simulating synclinal geological folds

Abstract

This paper studies three-dimensional convective regimes of a binary mixture in a system of three porous bent layers, simulating a synclinal geological fold under the influence of a geothermal temperature gradient. The layers are assumed to have identical porosities and different permeabilities. A mixture of tetralin and dodecane taken in equal proportions is considered as the fluid saturating the porous medium. The components of the mixture represent the groups of hydrocarbons found in oil fields. The numerical study is performed to evaluate the linear stability of the mechanical equilibrium of a binary mixture in the inclined porous layer saturated with liquid in a gravity field under the influence of a strictly vertical temperature gradient. The convection threshold found is compared with the threshold obtained for the system with non-linear stability. In three-dimensional nonlinear calculations for a three-layer mixture, the permeabilities of all three layers are varied. Here it is assumed that the permeabilities of the outer layers are identical and always lower than the permeability of the inner layer. It was found that when the permeability of the inner layer is much higher than the permeabilities of the outer layers, the flow is localized in the inner layer. When the permeabilities of the outer and inner layers are sufficiently close, the flow is localized near the outer boundaries of the fold, even if the inner layer is more permeable than the outer layers. As the supercriticality increases, the formation of longitudinal rolls is observed in the initially plane-parallel flow (within each fold limb), and the flow becomes spiral. A further increase in supercriticality leads to a predominance of the longitudinal roll component in the flow and an increase in the number of longitudinal rolls along the fold limb (increase in the wave number of longitudinal rolls).