Abstract
A karst system remains difficult to characterize especially when it comes to its conduits pattern and morphology. Even though speleology allowed to map the geometry of different cave systems, the majority of these systems remain unreachable underground. It has been observed that karst cavities often develop along features such as fractures and bedding planes in limestone reservoirs. In this study, we use a reactive transport model that simulate dissolution processes in fracture networks to investigate the effect of DFN properties (i.e. structure, anisotropy, connectivity) on incipient karst conduit geometry under different boundary conditions (constant head versus constant rate condition, directional versus concentrated recharge condition). We focused on single fracture (with/without cementation) and ladder like fracture networks which are common on limestone. Results showed that fracture networks properties have a considerable effect on the final geometry and topology of the incipient karst conduit patterns. For instance, the presence of cement on a single fracture showed a more localized dissolution comparing to non-cemented fracture that showed wider wormholes. Moreover, anisotropy of the fracture network affects the angularity of the incipient karst conduits; angular shapes for anisotropic initial DFNs and curvilinear for isotropic initial DFNs. Also, the connectivity of DFNs in different direction has a great impact on wormholes tortuosity, spacing and direction. Results also point out that the existence of long fractures set perpendicular to the main direction of flow plays a big role during dissolution processes; not only it affects the final geometry and topology of the pattern but also the distribution of incipient karst conduits diameters (decrease in the number of fracture segments with high conduit diameter). Finally, the type of BC remains a major factor that governs dissolution processes.