HR: 1330h
AN: H42F-1144    [PDF]
TI: Part I - In Situ Characterization Of Hydromechanical Coupling Between Stress And Permeability Of Single Fractures From Bore Hole Coupled Pressure-Deformation tests : Experiments In The Coaraze Fractured Rock Reservoir (France).
AU: * Yves, G
EM: guglielmi@geoazur.unice.fr
AF: Geosciences Azur, 250, rue A. Einstein - Les Lucioles I - Sophia Antipolis, Valbonne, AM 06560 France
AU: Frederic, C
EM: cappa@geoazur.unice.fr
AF: Geosciences Azur, 250, rue A. Einstein - Les Lucioles I - Sophia Antipolis, Valbonne, AM 06560 France
AU: Pascal, F
EM: fenart@geoazur.unice.fr
AF: Geosciences Azur, 250, rue A. Einstein - Les Lucioles I - Sophia Antipolis, Valbonne, AM 06560 France
AU: Arnaud, C
EM: charmoille@geoazur.unice.fr
AF: Geosciences Azur, 250, rue A. Einstein - Les Lucioles I - Sophia Antipolis, Valbonne, AM 06560 France
AB: In order to characterize the effect of hydromechanical coupling on the permeability of single fractures inside a fractured rock mass, we carried out pressure-deformation jacking tests into boreholes in the natural Coaraze laboratory. This site is a 19000~$m^3$ fractured calcareous reservoir where repetitive hydraulic loadings are produced by the closure of a floodgate located on a spring, at the downstream of the site. Simultaneous normal deformation and pressure measurements in several fractures and in the rock matrix show that the rock mass behaves elasticaly and that micrometric deformations mainly concentrate along fractures. Calculated normal stresses on the fractures range between 60 and 130~kPa. Jacking tests were done on 6 fractures, and repeated for 30 and 50~kPa hydraulic loadings in order to quantify fracture permeability variations. Single fracture planes were isolated by two packers between which a device allowed the measurement of pressure and deformation normal to the fracture plane. Before the experiment, initial pressure in the fracture between the packers was constant. The tests consisted in water injection with a small overpressure that did not exceed 25% of the initial pressure in order that it did not influence the fracture surrounding rock volume. Permeabilities were deduced with a 25% uncertainty. For the 50~kPa loading experiment, permeabilities cluster in two groups, high permeable fractures (group 1) ranging between 300 10$^{-5}$ and 130 10$^{-5}$ m$^2$.s$^{-1}$ and, low permeable fractures (group 2) ranging between 4 and 60 10$^{-5}$ m$^2$.s$^{-1}$. When the hydrostatic loading is decreased to 30~kPa, there is a 50 to 60% variation of the two groups permeabilities characterized by an increase of group 2 permeabilities and a decrease of group 1 permeabilities. Opposite behaviors of groups 1 and 2 highlight two very different hydromechanical effects. When the floodgate is closed, group 1 fractures are quickly filled with water because they are very permeable, and their deformation instantaneously follows pressure variations, a normal opening with a pressure increases and a normal closure with a pressure fall. Group 2 fractures are filled with water with a delay of several minutes to several hours because they are low permeable. During this delay, their deformation is mainly influenced by group 1 deformation. This experiment shows that the permeability of fractured rock masses is very sensitive to stress changes at shallow depth (or low in-situ stress) and that hydromechanical behavior of a few fractures have substantial effects on all the rock mass permeability.
DE: 1829 Groundwater hydrology
SC: Hydrology [H]
MN: 2003 Fall Meeting