Résumé
Les processus de couplages hydromécaniques dans un massif rocheux fracturé sont étudiés à travers des expérimentations in situ et des simulations numériques. L’approche expérimentale consiste à mesurer simultanément la pression de fluide et le déplacement mécanique en différents points d’un réservoir carbonaté tout en contrôlant les conditions aux limites hydrauliques. Ces mesures sont analysées par modélisation couplée hydromécanique. A l’échelle du massif, mesures et modèles montrent que le couplage hydromécanique est contrôlé par un comportement hydraulique de double perméabilité de fractures associé à un comportement mécanique de double rigidité de fractures. A l’échelle de la fracture unique, des mesures dynamiques par capteurs à fibre optique réalisées lors d’un pulse de pression montrent une réponse pression/déplacement présentant une boucle caractéristique dont l’évolution est différente entre les phases d’augmentation et de chute de pression. A partir de ces données in situ, les paramètres hydromécaniques des fractures et de la matrice rocheuse sont rétro-analysés par les modèles numériques. Ces modélisations montrent que la sensibilité de la réponse hydromécanique de la fracture pressurisée est fortement dépendante de la raideur normale et de l’ouverture hydraulique de la fracture, de la raideur de la matrice rocheuse et de la géométrie du réseau de fractures.
Abstract
Hydromechanical coupled processes in a shallow fractured rock mass were investigated in situ through field experiments and numerical simulations. The experimental approach consists of performing simultaneous and multi-frequency measurements of fluid pressures and displacements at different points and on different fracture types within a carbonate reservoir. Two kinds of experiments were conducted at the Coaraze Laboratory Site (France):
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1.
At the fracture network scale, a global hydraulic loading by groundwater level change shows that the coupling between fluid flow and deformation is simultaneously governed by a dual-permeability hydraulic behaviour and a dual-stiffness mechanical behaviour. The following fluid flow and hydromechanical conceptual scheme was established: first, a transient flow only occurs in faults with high permeability; second, when a steady-state flow is reached in faults, water flows from faults into lower permeability bedding planes. The intact rock matrix is practically impervious but the connectivity between the discontinuities is high. When fluid pressure changes occur within the fracture network, the hydromechanical coupling is direct in the highly permeable faults where a pressure change induces a deformation change. No direct hydromechanical coupling occurs within the lower permeability zones where deformation is not directly correlated with pressure changes. This means that the mechanical deformation of the bedding planes and rock matrix is induced by the fault deformation.
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2.
At the single fracture scale, the hydromechanical behaviour was evaluated by performing hydraulic pulse injection testing. This test was monitored using high-frequency (f = 120 Hz) hydromechanical measurements conducted with innovative fiber-optic borehole equipment. The hydromechanical response is simultaneously monitored at two measuring points spaced about 1 m apart within the plane of the sub-vertical fracture. Observed fluid pressure versus normal displacement curves shows a characteristic loop-shaped evolution in which the paths for loading (pressure increase) and unloading (pressure decrease) are different. The test was evaluated by coupled hydromechanical modelling using a distinct element technique. By matching the loop behaviour, modelling indicates that the pulse pressure increase portion allows the fracture hydromechanical properties to be determined while the pulse pressure decrease portion is strongly influenced by the hydromechanical effects within the surrounding fractured rock mass. A sensitivity study shows that the key parameters to coupled hydromechanical processes in such fracture systems are the initial hydraulic aperture and normal stiffness of the fracture, the stiffness of the rock matrix and the geometry of the surrounding fracture network.
Références
Barker JA (1988) A generalized radial flow model for hydraulic testing in fractured rock. Water Resour Res 24(10):1796–1804
Barker JA, Black JH (1983) Slug tests in fissured aquifers. Water Resour Res 19:1558–1564
Black JH (1985) The interpretation of slug tests in fissured rocks. Q J Eng Geol 18:161–171
Bredehoeft JD, Papadopulos S (1980) A method to determine the hydraulic properties of thight formations. Water Resour Res 16:233–238
Cappa F, Guglielmi Y, Fénart P, Merrien-Soukatchoff V, Thoraval A (2005a) Hydromechanical interactions in a fractured carbonate reservoir inferred from hydraulic and mechanical measurements. Int J Rock Mech Min Sci Geomech Abstr 42:287–306
Cappa F, Guglielmi Y, Gaffet S, Lançon H, Lamarque I (2005b) Use of in situ fiber optic sensors to characterize highly heterogeneous elastic displacement fields in fractured rocks. Int J Rock Mech Min Sci Geomech Abstr (sous presse)
Cappa F, Guglielmi Y, Rutqvist J, Tsang C-F, Thoraval (2005c) A in situ coupled hydromechanical behaviour of a deformable rock fracture in an high-permeability fracture network: field measurements and numerical modelling. Int J Rock Mech Min Sci Geomech Abstr (soumis pour publication en Août)
Claesson J, Follin S, Hellström G, Wallin NO (1995) On the use of the diffusion equation in test case 6 of DECOVALEX. Int J Rock Mech Min Sci Geomech Abstr 32:525–528
Cook NGW (1992) Natural joints in rock: mechanical, hydraulic and seismic behaviour and properties under normal stress. In: Jaeger Memorial Didaction Lecture, Int J Rock Mech Min Sci Geomech Abstr 29:198–223
Cooper HH, Bredehoeft JD, Papadopulos IS (1967) Response of a finite-diameter well to an instantaneous charge of water. Water Resour Res 3:263–269
Cornet FH, Morin RH (1997) Evaluation of hydromechanical coupling in a granite rock mass from a high-volume high-pressure injection experiment: Le Mayet de Montagne, France. Int J Rock Min Sci Geomech Abstr 34:207
Cornet FH, Li L, Hulin JP, Ippolito I, Kurowski P (2003) The hydromechanical behaviour of a fracture: an in situ experimental case study. Int J Rock Min Sci Geomech Abstr 40:1257–1270
Cundall PA (1988) Formulation of a three-dimensional distinct element model—Part I. A scheme to detect and represent contacts in a system composed of many polyhedral blocks. Int J Rock Mech Min Sci Geomech Abstr 25:107–116
Gentier S, Hopkins D, Riss J (2000) Role of fracture geometry in the evolution of flow paths under stress. In: Dynamic of fluids in fractured rock, Geophysical Monograph 122:169–183
Guglielmi Y (1998) Hydromechanics of fractured rock masses: results from an experimental site in limestone. In: Rossmanith H-P (ed) Mechanics of jointed and faulted rock. Balkema, Rotterdam, pp 621–624
Guglielmi Y, Mudry J (2001) Quantitative measurements of channel-block hydraulic interactions by experimental saturation of a large, natural, fissured rock mass. Ground Water 39:696–701
Hakami E (1995) Aperture distribution of rock fractures. PhD Thesis, Royal Institute of Technology, Sweden
Henry JP, Sibai M (1997) Couplage hydromécanique dans les joints rocheux sous sollicitations normales: proposition de modélisation et comparaison avec l’expérience. Expérimentation et Calcul en Génie Civil 47(54):47–54
Hopkins DL (2000) The implications of joint deformation in analyzing the properties and behaviour of fractured rock masses, underground excavations and faults. Int J Rock Mech Min Sci Geomech Abstr 37:175–202
Hopkins DL, Cook NGW, Myer LR (1990) Normal joint stiffness as a function of spatial geometry and surface roughness. In: Rock Joints, Barton, Stephansson (eds) Balkema, Rotterdamm, pp 203–210
Jackson LB (1995) Digital filters and signal processing. 3rd ed, Kluwer, Dordecht
Jung R (1989) Hydraulic in situ investigation of an artificial fracture in the Falkenberg granite. Int J Rock Min Sci Geomech Abstr 26:301–308
Makurat A, Barton N, Rad NS (1990) Joint conductivity variation due to normal and shear deformation. In: Barton N, Stephansson O (eds) Rock Joints. Balkema, Rotterdam, pp 535–540
McElwee CD (2002) Improving the analysis of slug tests. J Hydrol 269:122–133
Myer LR (1991) Hydromechanical and seismic properties of fractures. In: Wittke W (ed) Proceedings of the 7th International Congress Rock Mechanics Aagen, Germany. Balkema, Rotterdam, pp 397–404
Myer LR (2000) Fractures as collections cracks. Int J Rock Mech Min Sci Geomech Abstr 37:231–243
Pyrak-Nolte LJ, Morris JP (2000) Single fractures under normal stress: the relation between fracture specific stiffness and fluid flow. Int J Rock Mech Min Sci Geomech Abstr 37:245–262
Raven KG, Gale JE (1985) Water flow in a natural rock fracture as a function of stress and sample size. Int J Rock Mech Min Sci Geomech Abstr 22:251–261
Rutqvist J (1995) Determination of hydraulic normal stiffness of fractures in hard rock from well testing. Int J Rock Mech Min Sci Geomech Abstr 32:513–523
Rutqvist J, Stephansson O (1996) A cyclic hydraulic jacking test to determine the in situ stress normal to a fracture. Int J Rock Mech Min Sci Geomech Abstr 33:695–711
Rutqvist J, Stephansson O (2003) The role of hydromechanical coupling in fractured rock engineering. Hydrogeology J 11:7–40
Rutqvist J, Tsang CF (2002) A study of caprock hydromechanical changes associated with CO2-injection into brine formation. Environ Geol 42(2–3):296–305
Rutqvist J, Noorishad J, Tsang C-F, Stephansson O (1998) Determination of fracture storativity in hard rocks using high-pressure injection testing. Water Resour Res 34:2551–2560
Sibaï M, Haji Sotoudeh M, Henry JP (1997) Etude expérimentale du couplage hydromécanique de joints rocheux. Revue Française de Géotechnique 81:33–39
Tsang CF (1999) Linking thermal, hydrological, and mechanical processes fractured rocks. Annu Rev Earth Planet Sci 27:359–384
Tsang YW, Witherspoon PA (1981) Hydromechanical behaviour of a deformable rock fracture subject to normal stress. J Geophys Res 86:9287–9298
Tsang YW, Witherspoon PA (1983) The dependence of fracture mechanical and fluid flow properties of fracture roughness and sample size. J Geophys Res 88:2359–2366
Wang JSY, Narasimhan TN, Tsang CF, Witherspoon PA (1977) Transient flow in tight fractures. Well Testing Symposium, Berkeley, pp 103–116
Witherspoon PA, Wang JSY, Iwai K, Gale JE (1980) Validity of cubic law for fluid flow in a deformable rock fracture. Water Resour Res 16:1016–1024
Zangerl C, Eberhardt E, Loew S (2003) Ground settlements above tunnels in fractured crystalline rock: numerical analysis of coupled hydromechanical mechanisms. Hydrogeol J 11:162–173
Zimmerman RW, Chen DW, Cook NGW (1990a) The effect of contact area on the permeability of fractures. J Hydrol, 139:79–96
Zimmerman RW, Chen DW, Long JCS, Cook NGW (1990b) Hydromechanical coupling between stress, stiffness and hydraulic conductivity of rock joints and fractures. In: Barton N, Stephansson O (eds) Rock joints proceedings of the International Symposium, Balkema, Leon
Remerciements
L’auteur remercie ses collaborateurs, Yves Guglielmi et Stéphane Gaffet (Géosciences Azur), Jonny Rutqvist et Chin-Fu Tsang (Lawrence Berkeley National Laboratory), Alain Thoraval et Medhi Ghoreychi (Institut National de l’Environnement et des Risques Industriels) pour leurs commentaires et le travail réalisé ensemble. Ce travail a été financé par l’INERIS dans le cadre du programme de recherche BCRD-DR02. Cette publication a reçu le prix Jean Goguel 2005, décerné par le Comité Français de Géologie de l’Ingénieur et de l’Environnement.
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Cappa, F. Rôle des fluides dans le comportement hydromécanique des roches fracturées hétérogènes: Caractérisation in situ et modélisation numérique. Bull Eng Geol Environ 65, 321–337 (2006). https://doi.org/10.1007/s10064-006-0043-4
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DOI: https://doi.org/10.1007/s10064-006-0043-4