An image analysis contribution to the study of transport properties of low-permeability crystalline rocks

Transport properties of the Charroux–Civray tonalite matrix were studied by a two-dimensional multi-scale model, based on image analysis procedures. The estimation of a transport coefficient of the matrix was obtained by combining the 2-D image of the spatial arrangement of primary mineral phases with the aperture distribution of microscopic pathways. The study focused on one fresh facies and one fairly altered facies. Connectivity of the fluid flow network varied according to the studied facies. It is shown that pathways inside dark minerals and quartz, exert a lower influence on the transport coefficient than pathways inside feldspars. Strong assumptions used in the presented numerical method do not allow direct comparison between real transport coefficients and factors determined by the model. However, for both facies studied, comparison between simulated transport coefficients and experimental permeability suggests that the calculation hypothesis needs to be improved: the real aperture of microcracks must be taken into account, and a large number of classes of aperture are required for this kind of simulation.