Predicting the transport properties of sedimentary rocks from microstructure

Hydraulic and electrical conductivity of sedimentary rocks are predicted from the microscopic geometry of the pore space. Cross-sectional areas and perimeters of individual pores are estimated from two-dimensional scanning electron microscope (SEM) photomicrographs of rock sections. Hydraulic and electrical conductances of the individual pores are determined from these geometrical parameters using Darcy's and Ohm's laws. Account is taken of random orientation of cross sections with respect to the channel axes, and for variation of cross-sectional area along pore length. The effective medium theory of solid-state physics is then used to determine an effective conductance of each pore. Finally, the pores are assumed to be arranged on a cubic lattice, which allows the calculation of overall macroscopic values for the permeability and the electrical conductivity.; The region of validity of the well-known Kozeny-Carman permeability formulae for consolidated porous media and their relationship to the microscopic spatial variations of channel dimensions are established. For highly inhomogeneous rock-pore-space systems, the validity of the critical path analysis for estimating the permeability of consolidated rocks is examined also.; Perimeter-area power-law relationships of pores in five sedimentary rocks are determined from SEM photomicrographs of thin sections. The perimeter-area power-law relationship of pores, along with a pore-size distribution and a classical model for permeability, is used to estimate the permeability.; Experimentally the electrical conductivity of a partially saturated rock has been studied. The effective resistivities (formation factors) of the specimens, with an electrolyte solution in the pores that are not occupied by a wetting fluid (paraffin wax), are measured at different saturations, after solidifying the wetting fluid in place. The experimental data is studied in light of the role of the pore structure in the wetting fluid invasion process with the aid of fluid distributions at each saturation regime, a complete rock pore cast, and its associated rock section. The surface conductance contribution of clay minerals to the overall electrical conductivity is assessed. The effect of partial hydrocarbon saturation on overall rock conductivity, and on the Archie saturation exponent, is discussed.; Analytical calculations of the capillary pressure-saturation function are conducted, based on the distribution of pore hydraulic radii and the area-perimeter power-law relationship for pores. The geometrical quantities are estimated from two-dimensional SEM photomicrographs of rock sections. Experimental capillary pressure-saturation curves are obtained using alloy Wood's metal, which allows for direct examination of occupied pore space after the experiment. Model predictions are compared to empirical capillary pressure curves to calculate average pore body and pore throat sizes and aspect ratios, and these are compared with values estimated from photomicrographs.; Experiments to study relative permeabilities of a partially saturated rock have been carried out in Berea sandstone using fluids that can be solidified in place. The effective permeability of the spaces not occupied by the wetting fluid (paraffin wax) or the nonwetting fluid (Wood's metal), have been measured at various saturations after solidifying each of the phases. The corresponding wetting and nonwetting fluid distributions at different saturations are presented and analyzed in light of the role of the pore structure in the invasion process, and their impact on relative permeability and capillary pressure. Irreducible wetting and nonwetting phase fluid distributions are studied. The effect of clay minerals on permeability is also assessed.