Scanning electron microscope study of pore systems in rocks

Pore systems in rocks are generally affected by grain size, shape, sorting, packing, nature of cementing materials, by detrital and authigenic pore fillers, and by the previously imposed pressure and temperature history. These variables, through their influence on the pore structure, control important petrophysical properties such as porosity, permeability, irreducible fluid saturation, formation resistivity factor, specific surface area, and velocities and attenuations of elastic waves. By presentation of photomicrographs, the scanning electron microscope (SEM), with its large depth of focus and magnification, is shown to reveal details of pore spaces of rocks in three dimensions. The pore systems of 42 rock samples, obtained from surface outcrops and during the drilling of oil wells, were examined. In most cases, the details of the pore structure would not have been possible to study under a light transmission microscope. SEM micrograph sequences of typical pore structures from the more extensive study were selected and are presented for one sandstone, one limestone, one dolomite, five shale, and two granite samples. It is suggested that maps of pore structures in rocks could be quantitatively obtained from overlapping stereo pairs of micrographs through use of photogrammetric techniques.