A Methodology to Hydraulically Parameterize Deformation Zones and Fracture Networks in Fractured Crystalline Rock Using Fracture Borehole Data and Inflow Data from Single- Hole Tests
Abstract
Three-dimensional, regional, numerical models of groundwater flow and solute transport in fractured crystalline rock are used for two sites in Sweden that are considered for geological disposal of spent nuclear fuel. The models are used to underpin the conceptual modeling that is based on multi-disciplinary data and include descriptions of the geometry of geological features (deformation zones and fracture networks), transient hydrological and chemical boundary conditions, strong spatial heterogeneity in the hydraulic properties, density driven flow, solute transport including rock matrix diffusion, and mixing of different water types in a palaeo-hydrogeological perspective (last 10,000 years). The general approach applied in the numerical modeling was to first parameterize the deformation zones and fracture networks hydraulically using fracture and inflow data from single-hole tests. Second, a confirmatory step was attempted using essentially the same groundwater flow and solute transport model in terms of grid discretization and parameter settings for matching three types of independent field data: 1) large-scale cross-hole (interference) tests, 2) long- term monitoring of groundwater levels, and 3) hydrochemical composition of fracture water and matrix pore water in deep boreholes. We demonstrate here the adopted modelling approach for the first step, i.e. hydraulic parameterization of deformation zones and fracture networks, using single-hole test data from the site investigations undertaken at one of the sites in Sweden (Forsmark). The adopted modelling approach combines a deterministic representation of the major deformation zones with a stochastic representation of the less fractured bedrock outside these zones using the discrete fracture network (DFN) concept. An exponential model for the depth dependency of the in-plane deformation zone transmissivity was suggested based on the data. Lateral heterogeneity was simulated by adding a log-normal random deviate. A tectonic continuum is envisaged for the DFN concept where the number (intensity) of fractures of different sizes follows a power-law relationship. The methodology used to parameterise the discrete fracture networks starts with a connectivity-sensitivity analysis of different DFN models and ends with flow simulations using the most reliable DFN model deduced in the connectivity analysis. The flow simulations were carried out using three different kinds of correlations between fracture transmissivity and fracture size. For each correlation model, the model parameters were changed in a forward manner until a reasonable match against measured specific capacities (Q/Δp) was achieved.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.H41A0837F
- Keywords:
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- 1828 Groundwater hydraulics;
- 1829 Groundwater hydrology;
- 1830 Groundwater/surface water interaction;
- 1832 Groundwater transport;
- 1846 Model calibration (3333)