HR: 17:15h
AN: H24C-06    [Abstracts]
TI: In Situ Coupled Hydromechanical Effects In An High-Permeability Deformable Fracture: Numerical Analysis Of Pulse Test Signals
AU: * Cappa, F
EM: cappa@geoazur.unice.fr
AF: Geosciences Azur, CNRS-UNSA-IRD-UPMC, Sophia-Antipolis, 06 560 France
AU: Guglielmi, Y
H24C-06 AF: Geosciences Azur, CNRS-UNSA-IRD-UPMC, Sophia-Antipolis, 06 560 France
AU: Rutqvist, J
H24C-06 AF: Earth Sciences Division, Lawrence Berkeley National Laboratory, One cyclotron road, Berkeley, CA 94 720 United States
AU: Tsang, C
H24C-06 AF: Earth Sciences Division, Lawrence Berkeley National Laboratory, One cyclotron road, Berkeley, CA 94 720 United States
AU: Thoraval, A
H24C-06 AF: INERIS, Ecole des Mines de Nancy, Nancy, 54 000 France
AB: Coupled hydromechanical effects in a deformable vertical fracture located within a high-permeability fracture network are investigated in situ through hydraulic pulse tests. The tests were conducted using specialised borehole equipment that can simultaneously measure fluid pressure and fracture normal displacements. The field test data were evaluated for two measuring points spaced one meter vertically within the fracture. By plotting fracture normal displacement as a function of fluid pressure, field data show a characteristic loop in which the paths for loading (pressure increase) and unloading (pressure decrease) are different. This loop behaviour that is much different from laboratory results was analysed by series of coupled hydromechanical numerical modelling, with both distinct-element and finite-element modelling techniques and using two- and three-dimensional model representations that can incorporate various complexities in fracture network geometry. By matching this characteristic loop behaviour, the fracture normal stiffness and an equivalent stiffness of the surrounding rock mass can be back-calculated. Coupled hydromechanical modelling shows that initial fracture hydraulic aperture and normal stiffness vary by a factor of 2 to 3 for the two monitoring points within the same fracture plane. Moreover, the analysis show that hydraulic aperture and normal stiffness of the pulse-tested fracture, the stiffness of surrounding rock matrix, and the properties and geometry of the surrounding fracture network significantly affect coupled hydromechanical responses during the pulse injection test. The initial rising portion of the normal displacement-versus-pressure curve is highly dependent on the tested fracture's hydromechanical parameters and the stiffness of the matrix near the injection point (direct coupling effects), whereas the falling portion is highly influenced by mechanical processes within a larger portion of the surrounding rock (mainly indirect coupling effects).
DE: 1822 Geomechanics
DE: 1828 Groundwater hydraulics
DE: 1847 Modeling
DE: 1857 Reservoirs (surface)
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: Fall Meeting 2005