The Channel Network Model—A Tool for Transport Simulations in Fractured Media

Abstract

The Channel Network model and its computer implementation, the code CHAN3D, are presented for simulations of fluid flow and transport of solutes. The tool may be used to simulate and interpret field experiments of flow and transport on a large or small scale. It also may also be used for performance and safety assessments of repositories for nuclear and other hazardous wastes, e.g., chemical wastes. From observations in the field it is deduced that the flow and transport take place in a three‐dimensional network of connected channels. The channels have different properties and are generated in the model from observed stochastic distributions. This allows us to represent the large heterogeneity of the flow distribution commonly observed in the field. Solute transport is modeled considering advection and rock interactions such as matrix diffusion and sorption within the interior of the rock. For repository conditions the main contributions to the dispersion of solutes come from the large variation in the flow field (channeling) and the rock interactions. Objects such as fracture zones, tunnels, and release sources can be incorporated in the model. In addition, a methodology of how data may be obtained for the model is described. Data may be obtained from borehole and laboratory measurements.

Solute transport along a single fracture in a porous rock: a simple analytical solution and its extension for modeling velocity dispersion

“…15 Dependence of the breakthrough curves of the multichannel model on channel geometry together with its implementation into, e.g. the channel network model (Gylling et al 1999), will be made in the near future.…”

“…There is, however, still a long way to go before implementing it into, e.g. the channel network model (Gylling et al 1999) for safety and performance assessment of deep geological repositories for spent nuclear fuel. In particular, the capability and malleability of the multi-channel model in interpreting fieldscale experiments should be extensively studied in the near future.…”

“…For this reason, the new solution is extended into more general cases where a discrete or continuous set of flow channels is present in fractures in rocks, similar to the channel network model (Gylling et al 1999). This leads to a development of the multi-channel model in contrast to the singleflow-path model.…”

A methodology to interpret cross-hole tests in a granite block

“…Following Neretnieks (1983), it has become increasingly apparent that even within a fracture, water flow tends to concentrate through channels, which occupy a relatively small portion of the aquifer (Neretnieks, 1993;Tsang and Neretnieks, 1998). This led to the definition of channel network models, which can be viewed as a particular example of fracture network models, where preferential flow paths within fracture planes are represented through channels (Neretnieks, 1983;Moreno and Neretnieks, 1993;Gylling et al, 1999). Moreno and Tsang (1994) showed that channeling can be caused by multigaussian (i.e.…”

Solute transport in fractured rocks with stagnant water zone and rock matrix composed of different geological layers—Model development and simulations

“…Despite the complexities of the system, it is shown that the analytical solution to the Laplace‐transformed concentration at the outlet of the flowing channel is a product of two exponential functions; they describe the contributions of two partial systems in parallel in retarding solute transport, respectively. As a result, the Laplace‐transformed solution can readily be included in both the discrete fracture network models [ Dershowitz et al ., ] and the channel network models [ Gylling et al ., ] to describe solute transport through channels in heterogeneous fractured media consisting of an arbitrary number of rock units with piecewise constant properties. More importantly, the Laplace‐transformed solution suggests that the large number of different individual parameters can be grouped into a small set of parameter groups that considerably reduce the number of independent parameters.…”