Estimating CO2 Saturation from Resistivity Change for Monitoring CO2 Sequestration

Kyosuke Onishi¹, Yoshihiko Ishikawa¹, Ziqiu Xue², Kazuhiko Tsukada¹, Yasuhiro Yamada³, and Toshifumi Matsuoka³. (1) Department of Civil and Earth Resources Engineering, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto, Kyoto, 606-8501, Japan, phone: +81-75-753-4772, onishi@earth.kumst.kyoto-u.ac.jp, (2) CO2 Sequestration Research Group, Research Institute of Innovative technology for the Earth, 9-2 Kizugawadai, Kizu-cho, soraku-gun, Kyoto, 619 0292, Japan, (3) Dept. of Civil and Earth Resource Engineering, Kyoto University, Graduate School of Engineering, Kyoto, 6068501, Japan

The technique sequestering CO2 into the ground is a high degree of expectation for reducing CO2 emission. The realization of the CO2 sequestration into the coal seam or aquifer must require the confirmation of the stability in long term after the sequestration of CO2. It is considered that measuring electric resistivity is useful to monitor CO2 migration. Because CO2 is electrically bad conductor, the bulk resistivity of rock will increase when formation water is displaced to CO2 in pores.

This report shows the result of the examination of CO2 injection into rock cores in a pressure vessel, which create the same pressure and temperature in deep ground. We measured the change of electric resistivity of rock samples through the injection of CO2, which is composed of gas, liquid or super critical phase. The results indicate the increasing of electric resistivity with CO2 injection. Therefore, the method of electric exploration can observe the CO2 distribution in the ground. Also, we can calculate the replacement ratio using Archie's equation and the ratio is quite equivalent to the volume of input and output of the experimental system. The estimation from the electric resistivity is considered to have a high reliability.

A CO2 sequestration project was undertaken near Nagaoka in Japan and time-series well loggings were carried out in observation wells. We discuss the time-series CO2 saturation from resistivity change of logging data in the observation wells using Archie's equation in consideration of the results of the laboratory examination.

CO2 Sequestration – Concepts and Future Plans (EMD/DEG)
2006 AAPG International Conference and Exhibition, (November 5-8, 2006) Technical Program