A petrographic coded correlation between interface conductivity and other pore space properties

Electrical conductivity is an important property in geoscience and petroleum engineering. It gives not only information about the porosity and water saturation, but also about interfacial conductivity and about specific internal surface of the pore space. Archie’s equation correlates the electrical resistivity of a water-saturated rock sample and the resistivity of the pore water. A more detailed investigation with brine of different salinities results in the observation of interface conductivity, which is correlated to a specific internal surface. Measurements with increasing salinity of the brine were carried out on different samples: sandstone, carbonate and magmatic rocks. Additionally, permeability and effective porosity were determined. The resulting true formation factor and interfacial conductivity were then correlated with porosity and permeability. Analysis of data allows the application of the interface term as a measure of specific internal surface. For the interpretation of results, the simple capillary model a semi-empirical equation is used and delivers permeability as function of porosity, formation factor and interface conductivity. Determined permeability out of the calculations is compared with measured permeability. The developed equation which is dependent on the porosity, interface conductivity, formation factor and covers additionally the lithology influence can be used for a permeability calculation with a reasonable fit.