시추공간 전기비저항 탐사에서 겉보기 비저항의 거동특성

Abstract

The cross-hole resistivity method for detecting anomalous bodies have been the subject of a number of recent studies. In this study, we have analyzed the behavior of the apparent resistivity around a 2-D and a 3-D anomalous body using 2-D and 3-D cross-hole resistivity modeling programs. The finite difference method was adapted for 2-D modeling and the integral equation method for 3-D modeling. We have used the pole-pole array with a current electrode fixed at a point and the potential electrode movable around the anomalous body. Cross sectional variation in the apparent resistivity depend on the dimensionality of the body, the resistivity contrast between the anomalous body and the background medium and the shape of the body. Especially, 2-D and 3-D conductive body may produce quietly different apparent resistivity distribution, If an anomalous body is very conductive and its length in x direction is equal to or longer than that in z direction, the apparent resistivity due to 2-D and 3-D model shows opposite distribution to each other. Furthermore, the shape of the body also makes great changes in apparent resistivity distribution. These complex behavior of the apparent resistivity in cross-hole measurements with the pole-pole array make it difficult for a field operator to predict the true resistivity of the anomalous body. To overcome these problems, in-line data should be acquired and various alternative arrays can be considered.