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Fracture Characterization Using Borehole Radar: The Link Of Geophysical And Hydrogeological ModelNormal access

Author: Lanbo Liu
Event name: 17th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
Session: Groundwater Studies
Publication date: 22 February 2004
Organisations: EEGS
Language: English
Info: Extended abstract, PDF ( 743.65Kb )

Precise characterization of subsurface fractures (their orientation, aperture, distribution,
hydraulic conductivity, etc.) is critical to many geoscience sub-disciplines such as water resources
exploration and management, contamination remediation, underground construction, as well as
subsurface energy resource (hydrocarbon, geothermal, etc.) exploration and management. This paper
presents the forward modeling results of borehole radar signature of fractures generated by the
hydrogeological model of a fractured rock aquifer environment. A fracture system consists of interconnected,
permeable fractures filled with either freshwater, air, or brine and the isolated, nonpermeable
ones filled with only freshwater forms hydrogeological test model. The fracture groups were
statistically generated with different and desired features in space density, length, orientation and
aperture. Electromagnetic (EM) wave was generated with the finite-difference time-domain (FDTD)
forward modeling technique and propagated through the fractured rock aquifer models to form the
synthetic radar data sets. The features in radar syntheses were then examined and corresponded to
predefined fracture models. Based on the comparison, it shows that (1) the amplitude of radar waves
was generally diminished when brine replacing freshwater in the permeable fractures; (2) replacing
freshwater with air significantly increases the fracture fluid property contrast and results in significant
changes in some time records at certain transmitter-receiver configurations, depending on their relative
position to the permeable fractures; (3) in general, radar syntheses in reflection mode contains more
information on fracture properties than its transmission counterpart; (4) it is easier to identify more
fractures when air replacing water than brine replacing water. Combination of computer forward
simulation and field data reduction bears the hope to successfully characterize fractures for various
scientific and engineering purposes.

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