Determinação quantitativa de parâmetros texturais de arenitos eólicos através de análise de imagens digitais de seções delgadas

Abstract

Cutting sandstone samples from Piramboia and Botucatu formations, collected from a water well localized in Barretos city, Sao Paulo State, Brazil, were analysed in terms of microscopic digital image of thin sections to determine the porosity and packing index ( sensu Kahn 1956) of the sandstones. Two routines of digital image analysis were developed using thresholding segmentation method of the HSI (hue, saturation and intensity) components of the color image. The optical components of blue-dyed epoxy-impregnated sandstones samples are characterized by bluish pore space and uncolored grains and cements (non pore component), which present bimodal distribution of the optical component histograms, mainly hue component. The Piramboia and Botucatu formations are high porosity rocks, average 39,5% and 28,47%, respectively. The uppermost Piramboia Formation is characterized by the poorer porosity horizons (average 3,23%) due to the presence of carbonate cement. The packing of the sandstones are in general open, with indexes varying from 59% and 82% (density packing) and lower than 25% (proximity packing).