Development of Sectional Resistivity Image Analysis System and Its Application to Investigation of Fractured Rocks

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The instrument developed in this study consists of the current transmitting unit, the voltage receiving unit, the electrode switch unit, and the measuring cell. The section of the measuring cell is square (11cm by 11cm) and is surrounded by platinum electrodes at a spacing of 1cm.The software developed is based on the finite-element and iterative lest-squares methods. The accuracy and resolution attained by this software was tested through numerical experiment. While the result for a massive low-resistivity anomaly is satisfactory, it is found that the fracture-like conductive zone is reproduced as a broader anomaly.The system was first tested using a synthetic sample which simulates a fracture with a copper plate. This conductive target is clearly defined as a low-resistivity zone, but as in the numerical experiment the width of the image is larger than the true width. This result suggest, to some extent, the limitation of resolution inherent in potential measurement, but more work has to be done to define the attainable resolving power. The experiment using a sandstone with a fracture shows similar result.