![]() The injected fluid has a tendency to flow along the difficult-to-detect aperture between the medium and the confining cell plate. ![]() However, in the quasi-2d systems it is much harder to avoid the focusing of the flow at the boundary. In the 3D systems, by using the confining pressure at the perimeter of the sample, the core-flow is forced through the bulk of the rock matrix. In the lab experiments, two different setups are usually used: rock core acidization in Hassler cell and quasi-2D systems in Hele-Shaw cell which are aimed to study the dissolution in quasi-2D porous media and fractures. However, there are relatively few experimental studies on the onset of the instability, especially on the dissolution in the quasi-2D radial geometry. The theoretical and numerical predictions of the initial instability and the dissolution phase diagram have been compared to experimental results. At the onset of instability, a linear stability theory can be applied. ![]() Studies of the reactive-infiltration instability have been performed both theoretically and numerically. In the presence of flow, the dissolution front may become unstable, due to the so called reactive-infiltration instability. Another example is found in the geothermal industry where fluid dissolution is used to increase the surface available for the fluid flow in order to improve heat exchange in the fractures. An important application for the oil industry is acidization: the injection of a reactive liquid to increase the permeability of the oil reservoir near a production well. Reactive dissolution of fractures has also many engineering applications e.g., stability of dams and CO 2 storage. Examples of geological processes where reactive dissolution of fracture surfaces are important is weathering and diagenesis of rocks, and melt extraction from the mantle. ![]() Some of the structures resemble the forms seen in other phenomena in non-linear science such as dielectric breakdown, diffusion limited aggregation DLA, and structures observed in two phase flow in porous media. The detailed geometry of these patterns is of central importance for the flow and dispersion properties of the fractures. A variety of dissolution patterns have been observed to form on the fracture surfaces ranging from compact to ramified and fractal. If the fluid is reactive, the dissolution process will lead to structural alteration of the fracture surfaces. When a fluid flows in a fractured rock, the permeability of the fractures is usually much larger than the permeability of the porous matrix. We also analyze quantitatively the density of wormholes and the relation between the aperture roughness and the ramified patterns. Different dissolution patterns are presented in a phase diagram with the Péclet and Damköhler numbers as parameters. Here, we study dissolution in a radial geometry, which is relevant for a number of practical applications, e.g., the acidization of oil reservoirs. Dissolution patterns grow slowly, but they may lead to a dramatic reorganization of the flow. When an undersaturated reactive fluid is flowing in a fracture, the dissolution process will alter the flow paths locally.
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