The Effects of Salinity of Pore Water on Resistivity in Crystalline and Sedimentary Rocks
Koichi Suzuki
Central Research Institute of Electric Power Industry, Japan.
Contacts: k-suzuki@criepi.denken.or.jp (Koichi Suzuki)
Abstract
In order to reveal the influence of pore fluid resistivity (老w) on rock resistivity (老R), we use cylindrical shaped samples made by various rocks containing crystalline rocks and sedimentary rocks. The pore fluid in each sample was replaced by different concentrations of KCl solutions ranging from 20 ppm to 32,500 ppm. The rock resistivity of all samples increased with increasing pore fluid resistivity, however, it became almost constant at a point. These measured values indicate good agreement with the calculated curves based on the parallel resistance model containing the bulk surface resistivity (老c) by Katsube and Hume (1983). The relationship between porosity and formation facter (F) is better than that between porosity and 老c. The 老w-老R plots of fresh crystalline rocks or pre-Tertiary sedimentary rocks matched to Archie﹊s law when 老w is lower than 1次m, however, it becomes constant when 老w is higher than 10次m. Both F and 老c of crystalline rock samples decrease with the intensity of alteration, and that of sedimentary rocks decrease with the geological age. However, the 老w-老R plots of the part of Neocene sedimentary rocks, containing gravel or pumice, became constant when 老w is higher than 100次m. The F-老c plots indicated the plus-relationship like ﹍ellipse arc belt﹎ on the dual-logarithm plane. Whereas, the part of Neocene sedimentary rocks were positioned outside the belt. This result is interpreted that 老c becomes high because the specific surface of the samples is smaller than the others with the same values of F.
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Last modified: Thu Oct 24 10:44:06 2002