Consideration of Methodology for Estimating Hydrochemistry Based on Result of Resistivity Logging in Deep Boreholes

Abstract

This paper describes a methodology for calculating equivalent NaCl concentration of matrix pore water in the Tertiary sedimentary rocks based on the result of resistivity logging in deep boreholes at the Horonobe area, Hokkaido, Japan. Archie's law is used to calculate the equivalent NaCl concentration of matrix pore water. Consistency between the equivalent NaCl concentration calculated by Archie's law and the analytical data of pore water extracted from drilled core was statistically verified by t-test. As the result of the t-test, significant similarity between calculated NaCl concentration and analytical data was observed in nine out of eleven boreholes. In these boreholes, a good correlation was confirmed for both. It suggests that the equivalent NaCl concentration can be calculated based on the resistivity logging result. The significant difference found in two of the boreholes are considered to be due to contamination of pore water caused by penetration of drilling fluid into the rock matrix.

Based on these, attention points for estimating the equivalent NaCl concentration of matrix pore water from the resistivity logging result are summarized, and the procedure for applying at the field investigation is presented.