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| Titel |
Microcracks induced during dilatancy and compaction in a porous oolithic carbonate rock |
| VerfasserIn |
Jerome Fortin, Sergei Stanchits, Georg Dresen, Yves Guéguen |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250037377
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| Zusammenfassung |
| Reservoir rocks can undergo irreversible deformation (dilatancy or compaction) as a result of
a change in effective stress during production of hydrocarbon or during CO2 storage; and
whether deformation occurs in conjunction with dilatation or compaction, it has important
implications on fluid transport processes. In this study, we investigated the mechanical
behavior of the Chauvigny limestone. This porous limestone is one of the rocks, which
constitutes the Dogger, a deep saline aquifer, one of the favorable geological reservoirs for
CO2 storage in France. This limestone is an oolithic one and is characterized by a dual
porosity: a micro-porosity (inside the ooliths) of ~13% and a macro-porosity of ~4%. The
total porosity is ~17%.
Previous studies performed on limestone, even the ones with very low porosity like
Carrara marble, show at room temperature, a transition with increasing pressure from brittle
regime to catalastic flow. Two mechanisms are involved during failure of limestone: cracking,
and crystal plasticity, which can be activated at room temperature.
To investigate the brittle-ductile transition in this porous limestone, we performed 8
conventional triaxial experiments, at confining pressure in the range of 5-100 MPa, at room
temperature and at a constant strain rate of 2.10-4s-1. In addition, the evolutions of
elastic wave velocities were measured periodically with loading. The elastic wave
velocities are affected by two competing mechanisms: porosity reduction -which
increases the velocities-, and cracking -which decreases the velocities-. However
the elastic wave velocities are much more sensitive to cracking than to porosity
reduction.
Our results show that diltatant (nucleation and propagation of cracks) and compaction
micro-mechanisms (plastic pore collapse) compete. Two limit cases can be distinguished.
During hydrostatic compression, the inelastic volumetric strain seems to be mainly associated
with plastic pore collapse, whereas for the triaxial experiments at confining pressure <
30 MPa, the inelastic volumetric strain seems to be mainly associated with the
development of shear-induced cracks. For the triaxial experiments at confining
pressure > 30 MPa, we are able to distinguish a first critical stress state where
plastic pore collapse occurs, and a second stress state where shear-induced cracks are
initiated.
Reference:
J. Fortin, S. Stanchits, G. Dresen and Y. Gueguen, 2009. Micro-mechanisms involved
during inelastic deformation of porous carbonate rocks. Poromechanics IV, Proceedings
of the fourth Biot conference, edited by H. Ling, A. Smyth, and R. Betti, 378-38 |
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