Abstract
The fracture network modelling and hydrogeological assessment were performed in an 845 m deep borehole of the potential high-level waste repository formation and its caprock. The geometry of the fracture network was simulated using the discrete fracture network (DFN) modelling method, which is based on the geometric characteristics of the individual fractures. The hydrogeological evaluation was based on changes in porosity and permeability along the borehole using flow zone indicator (FZI) values that denote hydraulic flow units (HFU) within the rock body. Fracture network characteristics and hydrogeological features are mainly determined by the wellbore lithology, which can be divided into three zones. The sandstone body was intersected in the upper 300 m of the borehole, which forms a single HFU. The second zone was developed along with the transition zone between the sandstone and the underlying claystone bodies. Here the predominant rock type is claystone, but the characteristics of the fracture network are distinctly different from the deeper parts of this rock body. Below 400 m is the third zone, where distinct and extensive HFU-s could not form, probably due to different water–rock interaction processes that could have changed the porosity and permeability from point to point in the claystone.
Highlights
Several studies dealt with the potential host rock for a repository for high-level radioactive waste in Hungary [1]
The hydrogeological evaluation was based on changes in porosity and permeability along the borehole using flow zone indicator (FZI) values that denote hydraulic flow units (HFU) within the rock body
Fracture network characteristics and hydrogeological features are mainly determined by the wellbore lithology, which can be divided into three zones
Summary
Several studies dealt with the potential host rock for a repository for high-level radioactive waste in Hungary [1]. Using the Infress software, the fractured porosity and intrinsic permeability tensor elements can be calculated for each cubic volume element of the modelled rock body, if the aperture of the fractures is known [40]. To estimate the permeability tensor with the Infress code, a rock volume of d3 was considered, where d is the length of the interval used for well-hydraulic measurements, usually 20 m. In this way, an average aperture coefficient could be calculated for each interval independently so that the effective porosity can be calculated for all sections afterwards. Where FZI is the flow zone indicator in μm, NPI is the normalised porosity index, RQI is the reservoir quality index, k is the permeability in mD and Φ is the porosity in a volume fraction
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