Improved Glass Micromodel Methods for Studies of Flow and Transport in Fractured Porous Media

Abstract

Microscale experiments can provide mechanistic insights into larger‐scale flow and transport phenomena. Studies of the microscale mechanics involved in preferential flow in general, and unsaturated fast flow paths in particular, require the development of new experimental techniques. A new method for constructing glass micromodels has been developed which permits direct visualization and quantification of flow and transport phenomena in fractured porous media. In the fracture‐matrix micromodels a sequential etching procedure was developed in order to provide the necessary contrast of depths between matrix pores and fracture apertures. This high contrast in etching depths ensures that very different capillary properties are associated with micromodel “fractures” and “matrix” blocks. Improved techniques were also developed for reducing the pore sizes of the matrix to a natural fine‐grained sandstone pore scale. The improved micromodel pattern designs allow for previously unachievable control of boundary conditions. Various saturated and unsaturated fracture flow and transport processes can be visually and quantitatively studied with these micromodels. A method for directly measuring pore‐scale flow velocity distribution through tracing trajectories of suspended fluorescent microspheres was also developed. Examples of applications include measurements of velocity profiles in fractures, imbibition, fracture‐matrix transient flow, and matrix diffusion. In general, the improved micromodel method provides a unique tool for exploring some of the previously unrecognized flow and transport processes in fractured porous media. This research is directed at providing microscale explanations to some currently unresolved flow and transport issues important in predicting the larger‐scale flow processes.