Incipient karst generation in three-dimensional jointed layered rocks: influence of aperture configurations and flow boundary conditions

Karst aquifers provide considerable groundwater resources and supplies in many countries of the world. Karst systems exhibit complex spatial distributions of conduits, caves and vugs, but speleogenesis modeling remains very limited at aquifer scale. Early stage of wormholes development generally controls the final pattern of karst due to the positive feedback loop. In this study, we analyze the incipient karst generation in 3D jointed carbonate rocks with multiple horizontal layers, on the basis of numerical simulations. First, the fracture networks are generated while considering pseudo-mechanical rules for the nucleation and propagation of joints. Then, we analyze the impact of aperture configurations and flow boundary conditions on the dissolution patterns in such a 3D joint layered rock based on a developed hydro-chemical model. Preliminary results show that, for uniform apertures and horizontal flow, similar dissolution patterns are obtained whatever the flow orientations; bedding planes control and favor the tree-shape conduit networks while the joints promote the vertical spread. Results also show that karstification processes are dominated by the joint network structure and are significantly confined in individual layers when the aperture of bedding plane is lower than that of the joints. Changing flow boundary conditions (i.e. recharge and discharge from localized points instead of domain borders) tends also to induce different dissolution patterns. Compared to dissolution in a 2D fracture networks, these 3D reactive transport simulations further reveal the interaction of joint networks among different layers. This study has an important implication on understanding the initiation of different types of incipient karst patterns observed in nature.