Evolution of fracture aperture mediated by dissolution in a coupled flow channel–rock matrix–stagnant zone system
(English)Manuscript (preprint) (Other academic)
Fracture aperture is an important entity controlling fluid flow in natural fractures in rocks. The aperture of fractures in crystalline rocks may decrease or increase by different mechanical and chemical mechanisms. A model to describe the evolution of fracture aperture mediated by dissolution and precipitation is presented in this study. It includes advective flow in the fracture that can carry in or away dissolved minerals. The model also accounts for the fact that dissolved minerals in the fracture plane, in both flow channel and stagnant water zone, can diffuse into the adjacent porous rock matrix. The analytical solution obtained in the Laplace space is then used to study evolution of the fracture aperture under combined influence of stress and flow, in a pseudo-steady-state procedure. The simulation results give insights into the most important processes and mechanisms that dominate the fracture closure or opening under different circumstances. It is found that the times involved for any changes in fracture aperture are very much larger than the times needed for concentrations of dissolved minerals to reach steady state in the rock matrix, the stagnant water zone and the flow channel. This suggests that the steady state model can be used to assess the evolution of concentration of dissolved minerals in the rock fracture. Moreover, it is shown that diffusion into the rock matrix, which acts as a strong sink or source for dissolved minerals, clearly dominates the rate of concentration change and consequently the rate of evolution of the fracture aperture.
Fracture aperture, Dissolution, Rock matrix diffusion, Fluid flow, Channeling, Modeling
IdentifiersURN: urn:nbn:se:kth:diva-183773OAI: oai:DiVA.org:kth-183773DiVA: diva2:913009
QS 20172016-03-182016-03-182016-03-18Bibliographically approved