Présentations Colloques

Oral Presentation
Session 8.05: Karst aquifers
Massonnat Gérard
An innovative method for modeling the karstogenesis in carbonate reservoirs
Forecasting the 3D organisation of a karst network is a challenging issue since the complexity of the system is dependent on various embedded parameters - i) the heterogeneity of the matrix medium of the series in which the network has been created, ii) the multi-scales fracture network that partially drives the spatial distribution of dissolution features, iii) the multi-stages development of the karstic network through geological times, with multiple flow gradients and location of water tables. Consequently, the modeling of karstic aquifers requires to be driven by pre-existing heterogeneity in order to produce realistic images of heterogeneity.**A very new method for simulating karstogenesis among other diagenetic phenomena has been developed using a cellular automaton. A lattice gas in which particles are moving mimics the fluid transportation in the aquifer and its effects on reservoir properties. The Langevin equation is solved through a stochastic process that involves both advective and dispersive flows. According to the location in the model, the original properties of the matrix, the existence of any discontinuity like pre existing fractures or beddings, particles flow in the model and modify the medium, enlarging karst conduits thanks to the memory effect.**Several types of karstic reservoirs can be simulated using this innovative methodology - i) the very classic meteoric karst, with the possible representation of the epikarstic, unsaturated and saturated zones, ii) the hydrothermal karst, for which the advective flow is vertical, iii) the island karst, in which dissolution occurs in the mixing zone between the fresh water lense and the marine water. The methodology has been successfully applied on several field cases, and has been matched on actual values of karstic porosity and permeability. **