INFLUENCE OF MEASUREMENT SCALE ON PORE STRUCTURE DISTRIBUTIONS IN MOLDIC AND VUGGY LIMESTONES: AN EXAMPLE FROM THE CASTLE HAYNE AND BISCAYNE AQUIFERS

In order to better understand karst aquifers, detailed investigation of 2D porosity and pore geometry using image and geospatial analysis were undertaken. In this study, the porosity structures of moldic and vuggy karst aquifers are compared and contrasted by quantifying 2D porosity and pore geometry from optical televiewer, slabbed core, and thin-section images. The procedure for converting optical televiewer, slabbed core and thin-section images to a GIS useable format consisted of techniques that are typically used in remote sensing and image analysis applications. In GIS, vector formats were used to assess pore attributes (e.g., area, perimeter and shape index) and structure. Results show that both pore area and perimeter for the Spring Garden Member of the Castle Hayne and Miami Limestone Formation of the Biscayne aquifers can be described by exponential distributions. In both sets of images at all scales the relatively small pores have the highest occurrence, whereas larger pores occur less frequently. In the televiewer images, the smallest pores from the Castle Hayne aquifer are more complex than those in the Biscayne aquifer. Shape index is used as a measure of shape complexity and allows for a direct comparison of shape between the two aquifers. In core images, the sizes of the pores from both aquifers were identical but the pores from the Castle Hayne aquifer were more complex. In Castle Hayne thin-section images smaller pores have larger perimeters, but complexities of the shapes are similar to those of the Biscayne thin-sections. Results suggest that the scale of measurement affects the distribution of pore attributes. This study illustrates the importance of considering the scale of observation when evaluating quantitative characteristics of pore structure in karst limestone.