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We develop a new numerical model that couples hydraulic, mechanical and chemical processes to investigate the dynamic influence of stress on incipient karst formation in natural fracture networks. Our geological models are constructed based on realistic fracture patterns mapped from outcrops, which capture a wide range of spatial distribution and organization of carbonate fracture networks. We simulate the dissolutional growth of karst conduits in the fractured formation under varied initial aperture distribution and in-situ stress loading. We found that the impact of the stress effect on karstification depends on the relative relationship between the flow direction and the structural anisotropy of the fracture network. When the flow occurs in the direction corresponding to the most continuous fracture network structures, karst conduits only develop locally along a few long fractures with an orientation favorable to frictional sliding under the differential stress. Indeed, the important shear-induced dilation of these fractures generates a higher aperture and thus hydraulic conductivity. In contrast, when flow is in the direction transverse to the most continuous fractures, the far-field stress loading has a negligible impact on the emergent dissolution pattern but a perceptible impact on the onset time of breakthrough. In this later case, the developed conduits are much more tortuous with many branches. In both cases, the presence of initial aperture variability facilitates the development of a uniform dissolution front and therefore delays breakthrough. Our results demonstrate that the heterogeneity induced by geometrical complexities, enhanced by in-situ stress conditions, may play a decisive role on the karstification processes in fractured rocks. The results from this research provide important insights into the spatial relationship between tectonic structures, geomechanical constraints and karstogenesis. [ABSTRACT FROM AUTHOR]

Karst aquifers are highly heterogeneous hydrosystems where the geological structures that control the main flow paths exhibit complex geometry and topology. To get a better understanding of hydrodynamics of karst aquifers, it is important to understand how karst conduits form in response to carbonate dissolution in intricate fracture networks. The perturbation induced by aperture growth may have significant consequences on the scaling behavior of fracture network permeability. Therefore, we develop a numerical model, coupling the hydraulic and chemical processes governing the karstification processes, to investigate the influence of structural heterogeneities on the generation of incipient karst and better assess the evolutionary trajectories of natural karst systems.The evolution of conduit aperture is estimated based on a quasi-steady approximation of the sequentially coupled processes. The reactive transport problem is then solved on a synthetic discrete fracture network model. We consider realistic geometry and topology of natural joint networks. Initial aperture variability of joints obeys lognormal distributions. Previous simulations showed the importance impact of the fracture network topology on flow organization within the network. Here, the influence of the additional structure complexity induced by aperture variability on dissolution patterns is investigated. Results show that conduit networks of very different geometry emerge when different realizations of aperture models are imposed onto the same fracture network. Simulations also showed that the favored locations for the development of dominant conduits depend highly on the hydraulic connection between multiple dissolution paths competing for flow. The impact on the aperture growth on the flow exchange between dissolving fractures and ambient matrix is also considered. [ABSTRACT FROM AUTHOR]