Structural permeability of fluid-driven fault-fracture meshes

Structural permeability of fluid-driven fault-fracture meshes Fluid redistribution in the crust is influenced by hydraulic gradient, by existing permeability anisotropy arising from bedding and other forms of layering, and by structural permeability developed under the prevailing stress field. Field evidence suggests that mesh structures, comprising faults interlinked with extensional-shear and purely extensional vein-fractures, form important conduits for large volume flow of hydrothermal and hydrocarbon fluids. Meshes may be ‘self-generated’ by the infiltration of pressurised fluids into a stressed heterogeneous rock mass with varying material properties, developing best where bulk coaxial strain is symmetric with existing layering, but they also form under predominantly simple shear. Fluid passage through such structures generates earthquake swarm activity by distributed fault-valve action along suprahydrostatic gradients that may arise from compaction overpressuring, metamorphic dewatering, magmatic intrusion, and mantle degassing. Within mesh structures, strong directional permeability may develop in the σ 2 direction parallel to fault-fracture intersections and orthogonal to fault slip vectors. In particular tectonic settings, this promotes strongly focused flow with high potential for mineralisation. Mesh activation requires the condition P f ~ σ 3 to be maintained for the structures to remain high permeability conduits, requiring fluid overpressuring at other than shallow depths in extensional-transtensional regimes. Favoured localities for mesh development include linkage structures along large-displacement fault zones such as dilational jogs, lateral ramps, and transfer faults. In some circumstances, mesh formation appears to precede the development of major faults. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Structural Geology Elsevier

Structural permeability of fluid-driven fault-fracture meshes

Journal of Structural Geology, Volume 18 (8) – Aug 1, 1996

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Publisher
Elsevier
Copyright
Copyright © 1996 Elsevier Ltd
ISSN
0191-8141
eISSN
1873-1201
D.O.I.
10.1016/0191-8141(96)00032-6
Publisher site
See Article on Publisher Site

Abstract

Fluid redistribution in the crust is influenced by hydraulic gradient, by existing permeability anisotropy arising from bedding and other forms of layering, and by structural permeability developed under the prevailing stress field. Field evidence suggests that mesh structures, comprising faults interlinked with extensional-shear and purely extensional vein-fractures, form important conduits for large volume flow of hydrothermal and hydrocarbon fluids. Meshes may be ‘self-generated’ by the infiltration of pressurised fluids into a stressed heterogeneous rock mass with varying material properties, developing best where bulk coaxial strain is symmetric with existing layering, but they also form under predominantly simple shear. Fluid passage through such structures generates earthquake swarm activity by distributed fault-valve action along suprahydrostatic gradients that may arise from compaction overpressuring, metamorphic dewatering, magmatic intrusion, and mantle degassing. Within mesh structures, strong directional permeability may develop in the σ 2 direction parallel to fault-fracture intersections and orthogonal to fault slip vectors. In particular tectonic settings, this promotes strongly focused flow with high potential for mineralisation. Mesh activation requires the condition P f ~ σ 3 to be maintained for the structures to remain high permeability conduits, requiring fluid overpressuring at other than shallow depths in extensional-transtensional regimes. Favoured localities for mesh development include linkage structures along large-displacement fault zones such as dilational jogs, lateral ramps, and transfer faults. In some circumstances, mesh formation appears to precede the development of major faults.

Journal

Journal of Structural GeologyElsevier

Published: Aug 1, 1996

References

  • Summary of the seismographic observation of Matsushiro swarm earthquakes
    Hagiwara, T.; Iwata, T.
  • Matsushiro earthquake swarm
    Ichikawa, M.
  • Damage zone geometry around fault tips
    McGrath, A.G.; Davison, I.

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