Incipient karst generation in jointed layered carbonates: Insights from three-dimensional hydro-chemical simulations
Résumé
We develop a hydro-chemical model to simulate incipient karst generation in three-dimensional (3D) jointed layered carbonates. The discrete fracture networks consist of fractures that are represented by two-dimensional (2D) planes. The numerical model couples the important physical processes of fluid flow, reactive transport, and dissolutional growth of fracture aperture. We represent the typical layered joint systems by the synthetic fracture networks composed of two jointed layers separated by a horizontal bedding plane. By considering a wide range of initial flow rates and aperture distributions of the joints and bedding plane, the combined effects of the penetration length and the flow localization on karst evolution are systematically investigated. The simulation results confirm that different flow regimes (i.e. joint-dominated, transitional, and bedding plane-dominated) may induce distinct features of incipient karst morphologies observed in nature (i.e. pipe-like, stripe-like and sheet-like), which is attributed to the flow reorganization and the scale alteration of effective flow region. We further found the diversity of morphologies also depends on the initial penetration length, which plays a primary role in controlling dissolution patterns in joint-dominated systems. In addition, introducing the second joint set results in distinct 3D flow structure and dissolutional behavior comparing to single joint system. Our findings highlight the importance of 3D hydro-chemical modeling for realistic engineering applications as the structural complexity of 3D fractured rocks may be underrepresented by the previous studies using simplified conduit networks.