Table Of ContentT h e r m o - H y d r o - M e c h a n i c al
Coupling in F r a c t u r ed R o ck
Edited by
Hans-Joachim Kumpel
Springer Basel AG
Reprint from Pure and Applied Geophysics
(PAGEOPH), Volume 160 (2003), No. 5-6
Editor(s):
Hans-Joachim Kumpel
Leibniz-Institute for Applied
Geosciences (GGA)
Stilleweg 2
D-30655 Hannover
Germany
e-mail: [email protected]
A CIP catalogue record for this book is available from the Library of Congress, Washington D.C.,
USA
Bibliographic information published by Die Deutsche Bibliothek
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ISBN 978-3-7643-0253-5 ISBN 978-3-0348-8083-1 (eBook)
DOI 10.1007/978-3-0348-8083-1
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© 2003 Springer Basel AG
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Contents
809 Introduction
H.-J. Kiimpel
813 Borehole Breakouts in Berea Sandstone Reveal a New Fracture Mechanism
B. C. Haimson
833 A Model for the Mechanical Behaviour of Bentheim Sandstone in the Brittle
Regime
E. Klein, T. Reusch!e
851 Failure Model and Spatial Distribution of Damage in Rothbach Sandstone in
the Brittle-ductile Transition
P. Besuelle, P. Baud, T. Wong
869 Velocity Measurements and Crack Density Determination During Wet
Triaxial Experiments on Oshima and Toki Granites
A. Schubnel, o. Nishizawa, K. Masuda, X. J. Lei, Z. Xue, Y. Gueguen
889 Permeability of Triaxially Compressed Sandstone: Influence of Deformation
and Strain-rate on Permeability
J. Heiland
909 Comparison of Measured and Modelled Hydraulic Conductivities of
Factured Sandstone Cores
S. Baraka-Lokmane, R. Liedl, G. Teutsch
929 An Integrated Study on Physical Properties of a KTB Gneiss Sample and
Marble from Portugal: Pressure Dependence of the Permeability and
Frequency Dependence of the Complex Electrical Impedance
S. Heikamp, G. Nover
937 Permeability-porosity Relationships in Rocks Subjected to Various Evolution
Processes
Y. Bernabe, U. Mok, B. Evans
961 Slow Crack Propagation and Slip Correlations
J. Schmittbuhl, A. Delaplace, K. J. Maloy, H. Perfettini, J. P. Vi/otte
977 Pressure Oscillation Effects on the Saffman-Taylor Instability
N. Gland, D. Pisarenko
989 A Unified Model for Characterisation and Mechanical Behaviour of Rock
Fractures
F. Lanaro, O. Stephansson
999 Analytical Model for Permeability Evolution in Microcracking Rock
G. D. H. Simpson, Y. Gueguen, F. Schneider
1009 A Simple Model for Deviations from the Cubic Law for a Fracture
Undergoing Dilation or Closure
S. Sisavath, A. Al-Yaarubi, C. C. Pain, R. W. Zimmerman
1023 Scale Effects Related to Flow in Rough Fractures
Y. Meheust, J. Schmittbuhl
1051 Triggering of Seismicity by Pore-pressure Perturbations: Permeability-related
Signatures of the Phenomenon
S. A. Shapiro, R. Patzig, E. Rothert, J. Rindschwentner
1067 Scale Dependence of Hydraulic and Structural Parameters in the Crystalline
Rock of the KTB
G. Zimmermann, H. Burkhardt, L. Engelhard
1087 Mechanisms of Pore Pressure-stress Coupling which Can Adversely Affect
Stress Measurements Conducted in Deep Tunnels
K. Evans, T. Dahlo, J.-A. Roti
1103 Role of Stress-controlled Flow Pathways in HDR Geothermal Reservoirs
T. Ito, K. Hayashi
1125 Porosity and Thermal Conductivity of the Soultz-sous-Forets Granite
F. Surma, Y. Geraud
1137 Interrelations Between Thermal Conductivity and Other Physical Properties
of Rocks: Experimental Data
Y. Popov, V. Tertychnyi, R. Romushkevich, D. Korobkov, J. Pohl
© Birkhauser Verlag, Basel, 2003
Pure appl. geophys. 160 (2003) 809-812 I
Pure and Applied Geophysics
0033-4553/03/060809-4
Special issue 'Thermo-Hydro-Mechanical Coupling
in Fractured Rock'
Introduction
The supply and protection of groundwater, the production of hydrocarbon
reservoirs, land subsidence in coastal areas, exploitation of geothermal energy and
the long-term disposal of critical wastes or of C02 at depth are all issues of obviously
high socio-economic relevance. They all have in common to be closely related to
fluid flow in porous and/or fractured rock. In many cases the conditions of fluid
flow depend on the rheological behavior of rocks. Accordingly, mechanical
coupling between the liquid phase and the rock matrix can generally not be
neglected. The subject is receiving increasing interest from many researchers and
reservoir engineers.
Comprehensive insight into coupled processes of rocks and fluids is often
hampered due to the fact that rocks and rock formations are enormously complex.
Each rock sample consists of a myriad of mineral particles, forming its matrix, and of
fluid molecules residing in voids. Any two rock samples differ in their geochemical
constituents, size, and shape of grains, structure of pore space, fracture networks, etc.
Dealing with real rock material often means studying a system of a virtually infinite
number of unknowns. How do geologists, petrophysicists, reservoir engineers handle
such material?
A series of three Euroconferences on themes related to rock physics, rock
mechanics and fluid flow in rocks, all supported by the European Union, took place
in the years 1998, 1999, and 2000 (BOUTECA and GUEGUEN, 1999; COUPLES, MAIN,
and MEREDITH, 2000; KUMPEL, 2001). For the last event, approximately eighty
researchers met in November 2000 at Bad Honnefnear Bonn, Germany, to exchange
their latest knowledge and findings regarding thermo-hydro-mechanical coupling in
fractured rock. Thematic sessions during this meeting were
- Experiments and models of induced fracturing
- Fracture networks and transport properties
- Coupling between thermal, mechanical, and hydraulic properties.
The participants agreed that new insights are generally based on both,
experiments and numerical modeling, from the micro- to the macro- scale. For
instance, the development of fractures around boreholes and the formation of
H.-J. Kümpel (ed.), Thermo-Hydro-Mechanical Coupling in Fractured Rock
© Springer Basel AG 2003
810 Hans-Joachim KiimpeJ Pure app!. geophys.,
compaction bands in sandstones as a function of porosity and grain size was reported
to occur in a surprisingly variable manner. Laboratory tests have confirmed that
deformation can be extremely localized, even for seemingly homogeneous rocks.
Coupling between rock stress and fluid flow although affected by various
petrophysical quantities has been shown to be strongly dependent on the geometry
of fracture networks. Observations in a gallery have revealed that all permeable
fractures in crystalline rock were critically stressed so that they can be thought as
having formed under stress, whereas many non-permeable fractures were found to be
critically stressed as well, testifying the transient character of the status quo. Also,
seismicity that has been induced by massive hydraulic tests in many boreholes
worldwide appears to indicate a low mechanical stability of water saturated crustal
formations even down to depths of nine kilometers.
More general conclusions of the Bad Honnef Conference concern the suitability
of standard methods and of widely used parameters in describing coupled
phenomena in rocks. Models of a compact rock matrix with connected voids and
those of bonded aggregates of individual grains are two opposing, though valid
approaches to simulate transport of liquids through a porous medium. Application
of stochastic models and effective media concepts are important means to bridge
spatial gaps ranging from millimeters to kilometers, and the dynamics of processes
on time scales from seconds to hundreds of years.
However, a fundamental effective parameter like permeability, which by
definition is a measure of average transport of fluid volume through a hydraulically
conductive medium per time increment, may not always be a useful quantity. Large
scale field experiments have shown that fluid flow may be highly channelized and
that, depending on the specific site conditions, traditional upscaling can give
erroneous results. Ultimately, better understanding of the various physical processes
in fractured rock helps to improve predictions on how fluids can best be pumped out
of or injected into subsurface reservoirs, in which way toxic fluids are absorbed or
released by geologic formations, or to what extent rocks compact when pore fluids
are extracted.
Twenty articles, most of which were presented at the Bad Honnef Conference, are
contained in this special issue. Only a few of them deal with fully thermo-hydro
mechanical coupling. Rather, the individual investigations present contributions to
processes where such coupling is relevant. The special issue in whole covers aspects of
coupling from various points of view. Recent progresses made in understanding of
coupled phenomena in rock physics/rock mechanics is well documented in this
volume.
The first four articles describe findings from laboratory experiments that are
related to different types of sandstones and granites. They include processes like the
formation of compaction bands (contribution no. 1), fracture mechanics in the brittle
deformation regime (2), the spatial distribution of damage zones in stressed rock
samples (3), and the damage behavior of wet granites submitted to deviatoric stress
Vol. 160,2003 Introduction 811
(4). The next three papers extend these views by taking a closer look on parameters
that govern hydraulic diffusivity in sandstones and other types of rocks. Specific
targets addressed are the influence of differential stress on permeability (5), imaging
of the fracture geometry (6), and pressure induced variations in the pore geometry
(7). Contributions no. 8 to 10 cover investigations of permeability-porosity
relationships during rock evolution (8), of the formation, propagation, and
roughness of fractures in a plexi-glass block (9), and pressure oscillation effects of
two-phase flow under controlled conditions (10). The subsequent four articles
focus on diverse modeling approaches. Issues considered are how the geometry
and the mechanical behavior of fractures can be characterized by mathematical
expressions (11), how the evolution of permeability in a microcracking rock can
be expressed by an analytical model (12), deviations from the cubic law for a
fracture of varying aperture (13), and the numerical simulation of scale effects in
flow through fractures (14). Three further papers refer to in situ observations,
being related to topics as the assessment of in situ permeability from the spatio
temporal distribution of an aftershock sequence (15), to the scale dependence of
hydraulic pathways in crystalline rock (16), and to the significance of pore
pressure - stress coupling in deep tunnels and galleries (17). The last three
contributions deal with thermal aspects, namely, stress controlled pathways of
fluid flow in Hot-Dry-Rock reservoirs (18), relationships between porosity and
thermal conductivity for granite (19), and measurements of thermal conductivity
through optical scanning (20).
Many problems in rock physics and rock mechanics are still unsolved. Future
research should continue to focus on scaling rules - in both directions, i.e., on
upscaling and downscaling. Particularly poor knowledge seems to exist on
interactions between petrophysical and geochemical processes. What are the key
parameters in such type of coupling, and how can they be obtained? Findings from
experimental studies is and will remain an invaluable source for future progress in
understanding hydro-thermo-mechanical coupling in fractured rock. Nonetheless,
special attention must be paid to the question how site specific observations in the
field are. Given the complexity of the target material, an ever broader collection of
successful predictions and pitfalls forms our imagination of appropriate models, and
what aspects will continue to sharpen our insight into the multi-scale phenomena we
are encountering.
The papers collected in this volume provide some idea of the exciting meeting at
Bad Honnef. I would like to thank all the authors for contributing their original
articles to this special issue. The following reviewers are acknowledged for their
assistance: S. Baraka-Lokmane, B. Bourbiaux, M. Bouteca, D.S. Daev, C. David,
K. Evans, Y. Gueguen, B.C. Haimson, S. Heikamp, J. Heiland, T. Ito, E. Klein,
F. Lanaro, B. Maillot, Y. Meheust, G. Nover, D. Pisarenko, Y.A. Popov, T. Popp,
T. Reuschle, E.H. Saenger, J. Schmittbuhl, A. Schubnel, S.A. Shapiro, G.D.H.
Simpson, O. Stephansson, F. Surma, R.W. Zimmerman, G. Zimmermann.
812 Hans-Joachim Kiimpel Pure appl. geophys.,
REFERENCES
BOUTECA, M., and GUEGUEN, Y. (1999), Rock Conference Looks at Pore Pressure, Scale Effects, and
Deformation, EOS (Transactions American Geophysical Union), April 20, 188.
COUPLES, G., MAIN, I., and MEREDITH, Ph. (2000), Relationships between Damage and Localization: A
Eurocoriference on Rock Mechanics and Rock Physics, Newsletter Physical Properties of Earth Materials,
October 2000, 3-8.
KDMPEL, H.-J. (2001), Conference Addresses Thermo-hydro-mechanical Coupling in Fractured Rock, EOS
(Transactions American Geophysical Union), May 29, 248.
Hans-Joachim Kiimpel
Leibniz-Institute for Applied Geosciences (GGA)
Stilleweg 2
D-30655 Hannover
Germany
E-mail: [email protected]
© Birkhauser Verlag, Basel, 2003
Pure appl. geophys. 160 (2003) 813-831 I
Pure and Applied Geophysics
0033 -4553/03/060813-19
Borehole Breakouts in Berea Sandstone Reveal
a New Fracture Mechanism
BEZALEL C. HAIMSON1
Abstract-Vertical drilling experiments in high-porosity (22% and 25%) Berea sandstone subjected to
critical true triaxial far-field stresses, in which (lH (maximum horizontal stress) > (lv (vertical stress) > (lh
(least horizontal stress), revealed a new and non-dilatant failure mechanism that results in thin and very
long tabular borehole breakouts that have the appearance of fractures, and which counterintuitively
develop orthogonally to (lH. These breakouts are fundamentally different from those induced in crystalline
rocks, as well as limestones and medium-porosity Berea sandstone. Breakouts in these rocks are typically
dog-eared in shape, a result of dilatant multi-cracking tangential to the hole and subparallel to the
maximum far-field horizontal stress (lH, followed by progressive buckling and shearing of detached rock
flakes created by the cracks. In the high-porosity sandstone a narrow layer of grains compacted normal to
(lH is observed just ahead of the breakout tip. This layer is nearly identical to "compaction bands"
observed in the field. It is suggested that when a critical tangential stress concentration is reached along the
(lh spring line at the borehole wall, grain bonding breaks down and a compaction band is formed normal to
(lH. Debonded loose grains are expelled into the borehole, assisted by the circulating drilling fluid. As the
breakout tip advances, the stress concentration ahead of it persists or may even increase, extending the
compaction band, which in turn leads to breakout lengthening.
Key words: Rock mechanics, fractures, in situ stress, borehole breakouts, sandstone, compaction
band.
Introduction
Stress-induced instability around boreholes drilled vertically into the earth's
crust often results in 'breakouts' or zones of cross section elongation due to brittle
fracture at the borehole wall. Extensive field evidence and laboratory experiments
suggest that breakout orientation along the perimeter of such boreholes is typically
aligned with the direction of the minimum horizontal in situ stress (Jh (BELL and
GOUGH, 1979; SHAMIR and ZOBACK, 1992; HAIMSON and HERRICK, 1986; LEE
and HAIMSON, 1993). The compressive stress concentration there, generated by
the prevailing crustal stresses, is at its highest. Breakouts are at once both a cause
for concern regarding the borehole structural integrity, and potentially a most
I Department of Materials Science and Engineering, and the Geological Engr. Program, University of
Wisconsin, 1509 University Avenue, Madison, WI 53706-1595, U.S.A. E-mail: [email protected]
H.-J. Kümpel (ed.), Thermo-Hydro-Mechanical Coupling in Fractured Rock
© Springer Basel AG 2003
