HR: 1340h
AN: H33D-1610    [Abstracts]
TI: Detection and Characterization of Hydraulically Active Fractures in a Carbonate Aquifer: Results from Geophysical and Hydrochemical Measurements Along a 260-m-deep Borehole in the Combioula Geothermal System, Western Swiss Alps
AU: * Suski, B
EM: barbara.suski@unil.ch
AF: Faculty of Earth and Environmental Sciences, University of Lausanne, Lausanne, 1015, Switzerland
AU: Ladner, F
EM: florentin.ladner@geothermal.ch
AF: Geothermal Explorers LTD, Pratteln, Pratteln, 4133, Switzerland
AU: Baron, L
EM: ludovic.baron@unil.ch
AF: Faculty of Earth and Environmental Sciences, University of Lausanne, Lausanne, 1015, Switzerland
AU: Vuataz, F
EM: francois.vuataz@unine.ch
AF: Center for Geothermal Research c/o CHYN, University of Neuchatel, Neuchatel, 2009, Switzerland
AU: Holliger, K
EM: klaus.holliger@unil.ch
AF: Faculty of Earth and Environmental Sciences, University of Lausanne, Lausanne, 1015, Switzerland
AB: In mountainous regions, pronounced topography, complex geology, and highly permeable geological formations and/or deep-reaching faults and fractures largely govern the development of deep water circulations. In this context, fractured aquifers are of particular interest and the detection and hydraulic characterization of the fractures is a correspondingly important task. Here, in addition to traditional hydrogeological techniques, borehole geophysical measurements were conducted in a fractured deep carbonate aquifer located in the Combioula geothermal system in the western Swiss Alps. The objective of the study was to detect and characterize the hydraulically active fractures along a 260-m-deep borehole through the integration of a comprehensive suite of geophysical well-log data and hydrochemical analysis. Specifically, we wanted to relate the geophysical signals to the fracture network and to examine the sensitivity of the different methods to the flow of groundwater inside the fractures. Although a number of geophysical borehole logging techniques are known to be sensitive to the presence and physical character of fractures, most methods do not provide information with regard to their hydraulic activity. This problem is potentially alleviated through self-potential (SP) measurements, which exhibit a direct sensitivity to fluid flow. Our results illustrate the potential of SP logging for complementing other geophysical logging techniques for distinguishing between hydraulically active and non-active fractures as well as for determining the flow direction within the fractures. The results further indicate that the hydrochemical evidence proved to be critical for the interpretation of the SP measurements. This work may help to open the door for a quantitative interpretation of SP logs with regard to fracture permeability.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1835 Hydrogeophysics
SC: Hydrology [H]
MN: 2007 Fall Meeting