HR: 15:25h
AN: H33M-08    [Abstracts]
TI: Hydrostructural Characterization of Fracture Networks
AU: * Doe, T W
EM: tdoe@golder.com
AF: Golder Associates Inc., 18300 Union Hill Road, Redmond, WA 98052,
AU: Hermanson, J
EM: jhermanson@golder.com
AF: Golder Associates AB, Kappelgränd 7, Stockholm, S-10460, Sweden
AB: Over the past 30 years, research in underground laboratories for radioactive waste has led to the development of integrated site investigation and modeling methods for fracture networks. These activities began with the Stripa Project in central Sweden from 1977 to 1992 and have continued worldwide. Experiments on the scale of 100- 200 meter blocks have demonstrated the effectiveness of integrating testing during drilling, pressure monitoring, geologic description, flow logging, pressure transient testing, and groundwater chemistry to define fracture network geometries, particularly with respect to the identification of major features, background fractures, and compartmentalization. Major features are those large fractures or fracture zones that control the flow at the scale of interest, and must be simulated as deterministic features. Background fractures are defined stochastically, and provide connectivity between deterministic features. Based on the experience of block-scale investigations, it is possible to develop a clear picture of hydraulic networks using an integrated structural geologic, hydraulic, and hydrochemical approach. Although fracture network characterization requires a good geologic description of fractures and fracture zones from core and image logging, not all geologic features are water-conducting. Identifying water-conducting fractures begins with measurements of flow during drilling and flow logging immediately afterwards to identify significant conducting features. Major flow features must be hydraulically isolated using multiple point piezometer systems, if subsequent investigation methods are to be successful. Once installed, the pressure responses in the piezometers to subsequent drilling provide key information on connectivity and compartmentalization. Generally with three holes are sufficient to develop initial conceptual models of the major, controlling features. Subsequent boreholes test these geometric hypotheses and provide bases for their refinement. Confirmation of the network geometries comes from pressure transient testing. Although flow logging is very useful for locating conductive fractures, their steady-flow analysis methods do not allow for skin effects or accurate determination of hydraulic properties. Transient tests using single hole and interference data provide accurate hydraulic properties of the networks as well as insights to the network geometry and its boundaries. Geochemical data provide further constraints on connectivity and compartmentalization. The hydro-structural characterization of block scale experiments at the Äspö Hard Rock Laboratory provides an example of this integration approach.
DE: 1894 Instruments and techniques: modeling
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: 2007 Fall Meeting