No abstract

Determination of the initial saturation of a hydrocarbon reservoir requires resistivity log data and saturation exponent, A number of experimental investigations has shown that reservoir nettability affect the exponent value, A remarkable divergence conclusions, however, still appear in the literature.The objective of the present study was therefore to investigate the effect of rock nettability on saturation exponent. Fractal concepts have been applied to the image of thin-sections of a core sample and used to derive the resistivity equation. The advantage of this approach is that i{ is independent of rock-fluids equilibrium problems that commonly influence laboratory measurements, A general equation of electrical resistivity has been developed in this study. Electrical tortuosity, clay content, and rock nettability are incorporated in the equation. The present work employed twenty thin-sections of limestone and sandstones.It was found that the lowest exponent of 1.61 was obtained for strongly water-wet shaly sandstone and the highest value of 4,99 is for strongly oil-wet. The exponent consistently increases as the wetting condition is shifted from strongly water-wet toward oil-wet.It is close to 2.0 for clean sandstones at strongly water-wet, supporting the empirical formula of Archie.

Most correlation equations of rock permeability are usually based on the Euclidean geometry concept. Pore geometry and structure of most porous rocks are very complex, therefore non-Euclidean geometry concept, e.g. fractal theory, is needed to handle such a complexity. This paper presents a new equation for sandstone permeability involving other properties and fractal dimensions of pore space and surface. The equation is derived by combining Newton's Law of viscosity, Darcy equation, and fractal geometry concept. It is shown that parameters such as tortuosity, internal surface area, and shape factor can be replaced by fractal dimensions. As natural porous media are mostly anisotropic, this study enables us to identify factors that affect the anisotropy. Eighteen sandstone samples with porosity and permeability range from 21 to 37% and 2.76 to 3,644 millidarcies, were employed in this study. The pore space and surface fractal dimensions for each orthogonal direction for each sample was determined by box counting method. The results of this study demonstrate that calculated directional permeability of the high permeability samples is very close to the measured one after corrections were made for pore sizes of less than one micron. This finding suggests that micropores of the samples may be a major factor not contributing to fluid flow. For the low and medium permeability samples, however, an additional pore geometrical correction is needed. The additional correction factor is considerably different for different directions of fluid flow, indicating that the anisotropy is due to the difference in directional pore structural characteristics.