Petrophysical Analysis of Resistivity Data

Abstract

Ryjov developed forward problem of soil resistivity for sand-clay models. It uses 9 parameters (clay and sand porosity and capillary radii, water salinity and humidity, cation exchange capacity, temperature and clay content) to calculate soil resistivity. We applied these calculations for petrophysical analysis of sand clay soils using soil resistivity obtained from VES interpretation. It became clear that dependence of resistivity from clay content, porosity, cation exchange capacity, etc. allows solving inverse problem (estimation of petrophysical parameters on soil resistivity), that was fulfilled as algorithm and software in 2003. It is evident that we can’t determine all 9 parameters by using only soil resistivity; we need to find and use some additional information to have quantity of known parameters more than unknown ones. Temperature and groundwater salinity can be determined in each field site. We take soil samples to measure soil resistivity versus pore water salinity in laboratory to obtain soil model and recalculate resistivity data (cross-sections and maps) into cross-sections and maps of petrophysical parameters: clay content, porosity, cation exchange capacity, filtration coefficient, etc. After 2003 this technology was probed at more than 20 field sites in Mexico and Russia and demonstrated its efficiency.