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| Titel |
The hydro-mechanical properties of sealing horizons consisting of mechanical multilayers |
| VerfasserIn |
Carolina Giorgetti, Marco M. Scuderi, Massimiliano R. Barchi, Cristiano Collettini |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250130003
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| Publikation (Nr.) |
 EGU/EGU2016-10189.pdf |
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| Zusammenfassung |
| Sealing horizons are often sedimentary sequences characterized by alternating strong and
weak clay-rich lithologies. When involved in fracturing and faulting processes mechanical
multilayers, characterized by competence contrasts, develop complex fault geometries that
strongly influence their sealing maintenance. Here we investigate fault initiation and
evolution integrating field observations, on outcropping faults affecting a mechanical
multilayer, and rock deformation experiments, on the lithologies collected in the
field.
Faults initiate with a staircase trajectory that partially reflects the mechanical properties of
the involved lithologies, as suggested by triaxial and biaxial deformation experiments.
However, the small angles of fault initiation in calcite-rich (i.e. θi = 5˚ -20˚ ) and the high
angles in clay-rich layers (i.e. θi = 45˚ -86˚ ) indicate an important role played by
structural inheritance, i.e. joints and foliation, at the onset of fault development.
With increasing displacement (5 cm - 20 m), faults evolve towards more straight
trajectories and wider fault zones. At early stages fault rock consists of a calcite-rich
cataclasite. Then it evolves toward a well-organized marly foliated fault rock that
embeds sigmoidal fragments of limestones and localizes slip along surfaces where
ultra-cataclasite forms. The angles of fault reactivation concentrated between 30˚
and 60˚ , consistently with the low friction coefficient (μs = 0.3) measured in our
laboratory experiments, indicates that clay minerals exert a main control on fault
friction. Moreover, the presence of calcite mineralization in all the investigated
faults, i.e. within cataclastic fault rocks, dilational jogs and in form of slikenfibers,
suggests that faulting is the main mechanism allowing fluid flow within the sealing
horizon. This is supported by our triaxial deformation experiments showing fluid
flow across the sealing lithology only during the development of a thoroughgoing
fault.
Our integrated analysis indicates that incipient faults with a staircase trajectory promote
fluid flow through the opening of dilational jogs. With accumulating displacement, the
development of an impermeable foliated fault rock allows for fluid flow only during
fluid-assisted fault reactivation. This suggests that the overall fluid flow within the mechanical
multilayer is localized along small displacement faults and the sealing integrity can
be compromised only by larger faults cutting across the entire sealing horizon. |
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