NDLI: Role of fluids in the hydromechanical behavior of heterogeneous fractured rocks: in situ characterization and numerical modelling

Content Provider	Springer Nature Link
Author	Cappa, Frédéric
Copyright Year	2006
Abstract	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.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): 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. 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.
Starting Page	321
Ending Page	337
Page Count	17
File Format	PDF
ISSN	14359529
Journal	Bulletin of the International Association of Engineering Geology - Bulletin de l'Association Internationale de Géologie de l'Ingénieur
Volume Number	65
Issue Number	3
e-ISSN	14359537
Language	English
Publisher	Springer-Verlag
Publisher Date	2006-05-18
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Hydromechanical couplings Fractures In situ measurements Numerical modelling Flow Deformation Nature Conservation Geoecology/Natural Processes Structural Foundations, Hydraulic Engineering Applied Geosciences
Content Type	Text
Resource Type	Article
Subject	Geology Geotechnical Engineering and Engineering Geology

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