Crosshole surveys are used when two or more boreholes are present in order to provide the maximum imaging accuracy for the cross-section between respective boreholes.
Crosshole resistivity survey to find an aquifer zone
This crosshole survey was configured to find aquifer zones. As the figure shows below, only seven and 14 electrodes were used in the left and right boreholes respectively, due to site constraints. With a special data acquisition arrangement, 2,500 data points were collected within 10 minutes. The data points were then inverted into a true resistivity section.
It is apparent that a high resistivity band is located in the middle of the survey area, resembling a sandstone that decreases in thickness from right to left. Core logging showed that the sandstone's upper and lower s are comprised of calcareous lithology with high porosity and water content, thus low resistivity.
Crosshole resistivity survey to find industrial waste water
This exploration survey used the crosshole resistivity method to detect whether an industrial waste water leakage from an industrial waste water process pond existed. Chemical analyses concluded that this specific waste water has a much lower resistivity than normal water.
The figure below shows that the area above 45m is a relatively high resistive zone made of limestone. Below this depth is a middle resistive zone with some low resistivity bands visible; they are the source of possible leaks or fracture zones.
A borehole between ZK7 and ZK8 was drilled to test one of these low-resistivity locations. Polluted water was found at the depth of 52m. The figure below shows consistency among joints is also evident between each adjacent cross-hole. Detailed geological information can thus be obtained from this kind of resistivity survey.
ZZ Resistivity Imaging Pty. Ltd.
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Copyright: May 2020