EVOLUTION OF EARLY KARST IN COMPLEX FRACTURE NETWORKS: CHARACTERIZING THE EFFECT OF APERTURE HETEROGENEITY ON PREFERENTIAL FLOW PATH FORMATION

Karst features in limestone aquifers often exhibit highly heterogeneous patterns, which are strongly governed by structural complexities. Fracture networks dominate preferential flow pathways and mass transfer. Extensive field studies give overwhelming evidence of initial karst conduits proceeds along narrow joints and bedding planes. However, the classical approach to deduce the principles of cave evolution from the observation of geological structures of cave systems. The reactive transport model provides a quantitative approach to evaluate the parameter on preferential flow path in karst aquifer.

This work is intended to present comprehensive model to reveal percolation characteristic and dissolution process of stochastic primary fracture systems in limestone. Based on the embedded discrete fracture model, a Multi-scale modeling approach is proposed to describe fracture networks with different topology and various apertures. This model is verified against preexisting numerical models. We perform a 3-D field case study regarding hierarchical speleogenesis, based on karst terrain field data. Simulation results shows that the mechanism of flow focusing and reactive infiltration instabilities determines fracture dissolutional propagation. Patterns of local dissolution-induced alterations related to fracture permeability, hydraulic conductivity and extensive dissolution appeared in fracture tips and intersections.