Journal of Conference Abstracts

The Formation and Evolution of Layered Structures in Porous Media

Stan Schoofs (schoofs@geof.ruu.nl)¹, Ron A. Trompert (trompert@geof.ruu.nl)¹ & Ulrich Hansen (hansen@earth.uni-muenster.de)²

¹Utrecht University, VMSG, Budapestlaan 4, 3584 CD Utrecht, The Netherlands

²Instituet fuer Geophysik, Wilhelms Universitaet Muenster, Correnstrasse 24, D-48149 Muenster, Germany

Horizontally layered structures can develop in porous or partially molten environments, such as magma chambers, the Early Earth's mantle and hydrothermal systems. As a first order approximation, we have studied the formation and evolution of layers in a rigid porous medium, by heating a chemically stably stratified fluid from below.

Conservation of momentum of the incompressible fluid within the pores is represented by Darcy's law. Furthermore, we have considered both a simple (scalar) and more complex (velocity dependent) model for the dispersion of chemical components. The system of equations is solved by employing a control volume multigrid method. Initially, the fluid is cold, motionless and chemically stably stratified. In geological systems, porosity is typically very low. This leads to a higher advective speed of the solute, as compared to that of heat. Therefore, the influence of a low porosity on the layer formation is studied explicitly.

A staircase of separately convecting layers develops. Growth of a convective layer through convective entrainment, the formation of a stable density interface on top of the layer and destabilization of the next layer are closely coupled. The growth of a convective layer stops, when convective entrainment is replaced by purely diffusive (dispersive) transport of heat (solute) across the interface. This is different from layer formation as observed in Hele-Shaw cells, in which the layer growth terminates once a thermal equilibrium is reached. A simple force balance on a fluid parcel within the convective layer is proposed, as to determine the transition in the entrainment regime. In order to fit the force balance, a constant is introduced. This constant depends significantly on the employed dispersion model.