Abstract
This paper presents results of fractal analysis of fracture systems in upper Triassic dolomites in Žumberak Mountain, Croatia. Mechanical rock characteristics together with structural and diagenetic processes results with fracture systems that can be considered as fractals. They are scale-invariant in specific range of scales. Distribution of fractures can be than described with power law distribution and fractal dimension. Fractal dimension is a measure of how fractures fill the space. Fractal dimension can be estimated form photographs of outcrops by converting photographs to binary photographs. In binary photo there is only black (rock or fractures) and white (fractures or rock). Fractal dimension is then estimated based on box-counting method. In this paper we present results of fractal analysis from three outcrops. Results are very similar to previous published results from outcrops of dolomites in Slovenia. Obtained fractal dimensions are in range 2,69-2,78 and it depends on how fracture systems are distributed in the outcrop. Lower values indicate smaller number of fractures and higher significance of larger fractures. Higher values indicate distribution of more similar sized fractures throughout whole outcrop. Fractal dimension is very significant parameter in rock fracture system characterisation sense it describes how fractures are distributed in the outcrop. It can be used in discrete fracture network modelling if spatial distribution of fractures is represented with power law distribution.
Highlights
In northwestern Croatia, carbonate rock has a great hydrogeological potential with relatively low primary porosity but considerable secondary i.e. fracture porosity (Dragičević et al, 2014)
Photographs in a larger scale may show an unrealistic image of an outcrop, as in Pl 2 where Figure 8b shows only part of the layer which is compact and so the fractal dimension in that area is smaller than the rest
The obtained fractal dimensions are in the range 2,682,78 which is very similar to the results of fractal analysis in similar dolomites in Slovenia (Verbovšek, 2009)
Summary
In northwestern Croatia, carbonate rock has a great hydrogeological potential with relatively low primary porosity but considerable secondary i.e. fracture porosity (Dragičević et al, 2014). These are mainly dolomites of Upper Triassic age that are characterized by significant thicknesses and significant surface and subsurface distribution. The shallower structures regularly contain groundwater of high quality and the greater depths contain geothermal water or even hydrocarbons. These dolomites have great hydrogeological potential, their porosity distribution was never analyzed. Fracture systems in upper Triassic dolomites in Slovenia are recognized as fractal objects with power-law distribution and fractal dimension
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