Geophysical estimation of permeability in sedimentary media with porosities from 0 to 50%

Abstract

The main objective of this study is to find a relationship between permeability and porosity, in the range 0 up to 50%, so that the permeability could be estimated only through geophysical parameters. This relationship should be consistent with the statistically expected values in sedimentary basins, and it should include the positive correlation between permeability and porosity in consolidated media and the negative correlation in unconsolidated ones. We have also developed another relationship between formation factor and permeability, considering that the values of porosity and pore fluid resistivity are known from other sources different from resistivity logs. - The method for determining these relationships has been to generate functions with the expected geometry and to fit them to empirical data drawn from published papers. As a result we obtained a new relationship between porosity and permeability, with cementation exponent as added variable, and a new relationship for indirect estimation of permeability from the formation factor. Given the formation factor dependence with clay content, we have also developed a theoretical relationship to calculate the formation factor in a clayey media, assuming that clay content is known from other logs. In this relationship, we have not taken into account the presence of non-conductive liquid phases, such as oil. Comparison of the results obtained from these expressions with data collected in the literature leads to conclude that it is possible to determine the permeability of each layer in any zone from resistivity logs, if both the clay content and the resistivity of the interstitial fluid are known.