Characterisation of hydraulically-active fractures in a fractured granite aquifer

Abstract

In this study, the practical usefulness and fundamental applicability of a self-potential (SP) method for identifying the hydraulically-active fractures were evaluated by a comparison of SP methods with other geophysical logging methods and hydraulic tests. Potentially permeable fractures intersecting a shallow, 10-m borehole were first identified using conventional geophysical methods such as acoustic borehole televiewer imaging and temperature, electrical conductivity and gamma-gamma logs. These results were then compared to results of analysis using the SP method. Constant pressure injection and recovery tests were conducted for verification of the hydraulic properties of the fractures identified by various logging methods. The acoustic borehole televiewer and gamma-gamma logs detected the openings or weathering zones associated with fractures intersecting the borehole, but they could not prove that groundwater was flowing through the detected fractures.

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