A priori prediction of macroscopic properties of sedimentary rocks containing two immiscible fluids
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The processes in porous media governed by capillary forces, such as drainage and imbibition cycles, infiltration from surface water, flow, transport, adsorption and dissolution of contaminants, are of great importance in soil science, subsurface geochemistry, petroleum engineering, and hydrology. The methodology proposed in this work is devoted to the pore-scale modeling of such processes. The goal is to be able to make a priori predictions of the macroscopic properties of model sedimentary rocks, such as capillary pressure curves, interfacial area, relative permeabilities and electrical properties. The idea is to conduct a theoretical investigation in a simple but physically representative model porous medium. The model is a random packing of equal spheres for which the coordinates of the centers have been measured. Knowledge of the coordinates determines the grain space and the void space in the packing, thereby overcoming a long-standing difficulty for theoretical approaches to pore-level modeling. Geological processes, such as isopachous and pore-filling cementation, are simulated in the sphere pack, thus creating simple models of sedimentary rocks with predetermined pore space geometry. Despite the simplicity of the model porous medium, it is a powerful tool for investigation of the flow and transport in soils and sedimentary rocks. In particular it allows a priori predictions of macroscopic behavior. This capability is the most important aspect of the approach. Because there are no arbitrarily prescribed parameters, the predictions can be compared directly to experiments, providing a much stronger test than is possible with many other modeling approaches. For example, knowledge of the pore space geometry and wettability conditions allows computing the exact configuration of liquid phases in porous media. This capability enables the simulation of imbibition of a wetting phase into the model porous medium using a physically consistent dynamic criterion for the imbibition of individual pores. This approach allows a priori, quantitative prediction of the configuration of fluid phases during imbibition. This in turn allows a quantitative understanding of how different macroscopic processes and parameters (e.g. relative permeabilities or resistivity index) depend on the geologic (e.g. type and amount of cement) and physical (e.g. wettability) features of porous media.