Pore and throat size distributions measured from synchrotron X-ray tomographic images of Fontainebleau sandstones

The three-dimensional geometry and connectivity of pore space controls the hydraulic transport behavior of crustal rocks. We report on direct measurem ent of flow-relevant geometrical properties of the void space in a suite of four samples of Fontainebleau sandstone ranging from 7.5 to 22% porosity. The measurements are obtained from computer analysis of three-dimensional, synchrotron X-ray computed microtomographic images. We present measured dis tributions of coordination number, channel length, throat size, and pore vo lume and of correlations between throat size/pore volume and nearest-neighb or pore volume/pore volume determined for these samples. In order to deal w ith the ambiguity of where a nodal pore ends and a channel begins, we appor tion the void space volume solely among nodal pores, with the channel throa t surfaces providing the nodal pore delineations. Pore channels thus have l ength but no associated volume; channel length is defined by nodal pore cen ter to nodal pore center distance. For a sample of given porosity our measu rements show that the pore coordination number and throat area are exponent ially distributed, whereas the channel length and nodal pore volume follow gamma and lognormal distributions, respectively. Our data indicate an overa ll increase in coordination number and shortening of pore channel length wi th increasing porosity. The average coordination number ranges from 3.4 to 3.8 the average channel length ranges from 200 to 130 mu m, Average throat area increases from 1600 to 2200 mu m(2) with increasing porosity, while av erage pore volume remains essentially unchanged at around 0.0004 mm(3).