Permeability of fault-related rocks, and implications for hydraulic structure of fault zones

Permeability of fault-related rocks, and implications for hydraulic structure of fault zones The permeability structure of a fault zone in granitic rocks has been investigated by laboratory testing of intact core samples from the unfaulted protolith and the two principal fault zone components; the fault core and the damaged zone. The results of two test series performed on rocks obtained from outcrop are reported. First, tests performed at low confining pressure on 2.54-cm-diameter cores indicate how permeability might vary within different components of a fault zone. Second, tests conducted on 5.1-cm-diameter cores at a range of confining pressures (from 2 to 50 MPa) indicate how variations in overburden or pore fluid pressures might influence the permeability structure of faults. Tests performed at low confining pressure indicate that the highest permeabilities are found in the damaged zone (10 −16 –10 −14 m 2 ), lowest permeabilities are in the fault core (< 10 −20 –10 −17 m 2 ), with intermediate permeabilities found in the protolith (10 −17 –10 −16 m 2 ). A similar relationship between permeability and fault zone structure is obtained at progressively greater confining pressure. Although the permeability of each sample decays with increasing confining pressure, the protolith sustains a much greater decline in permeability for a given change in confining pressure than the damaged zone or fault core. This result supports the inference that protolith samples have short, poorly connected fractures that close more easily than the greater number of more throughgoing fractures found in the damaged zone and fault core. The results of these experiments show that, at the coreplug scale, the damaged zone is a region of higher permeability between the fault core and protolith. These results are consistent with previous field-based and in-situ investigations of fluid flow in faults formed in crystalline rocks. We suggest that, where present, the two-part damaged zone-fault core structure can lead to a bulk anisotropy in fault zone permeability. Thus, fault zones with well-developed damaged zones can lead to enhanced fluid flow through a relatively thin tabular region parallel to the fault plane, whereas the fault core restricts fluid flow across the fault. Although this study examined rocks collected from outcrop, correlation with insitu flow tests indicates that our results provide inexact, but useful, insights into the hydromechanical character of faults found in the shallow crust. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Structural Geology Elsevier

Permeability of fault-related rocks, and implications for hydraulic structure of fault zones

Journal of Structural Geology, Volume 19 (11) – Nov 1, 1997

Loading next page...
 
/lp/elsevier/permeability-of-fault-related-rocks-and-implications-for-hydraulic-TXAb0yAmkj
Publisher
Elsevier
Copyright
Copyright © 1997 Elsevier Ltd
ISSN
0191-8141
eISSN
1873-1201
DOI
10.1016/S0191-8141(97)00057-6
Publisher site
See Article on Publisher Site

Abstract

The permeability structure of a fault zone in granitic rocks has been investigated by laboratory testing of intact core samples from the unfaulted protolith and the two principal fault zone components; the fault core and the damaged zone. The results of two test series performed on rocks obtained from outcrop are reported. First, tests performed at low confining pressure on 2.54-cm-diameter cores indicate how permeability might vary within different components of a fault zone. Second, tests conducted on 5.1-cm-diameter cores at a range of confining pressures (from 2 to 50 MPa) indicate how variations in overburden or pore fluid pressures might influence the permeability structure of faults. Tests performed at low confining pressure indicate that the highest permeabilities are found in the damaged zone (10 −16 –10 −14 m 2 ), lowest permeabilities are in the fault core (< 10 −20 –10 −17 m 2 ), with intermediate permeabilities found in the protolith (10 −17 –10 −16 m 2 ). A similar relationship between permeability and fault zone structure is obtained at progressively greater confining pressure. Although the permeability of each sample decays with increasing confining pressure, the protolith sustains a much greater decline in permeability for a given change in confining pressure than the damaged zone or fault core. This result supports the inference that protolith samples have short, poorly connected fractures that close more easily than the greater number of more throughgoing fractures found in the damaged zone and fault core. The results of these experiments show that, at the coreplug scale, the damaged zone is a region of higher permeability between the fault core and protolith. These results are consistent with previous field-based and in-situ investigations of fluid flow in faults formed in crystalline rocks. We suggest that, where present, the two-part damaged zone-fault core structure can lead to a bulk anisotropy in fault zone permeability. Thus, fault zones with well-developed damaged zones can lead to enhanced fluid flow through a relatively thin tabular region parallel to the fault plane, whereas the fault core restricts fluid flow across the fault. Although this study examined rocks collected from outcrop, correlation with insitu flow tests indicates that our results provide inexact, but useful, insights into the hydromechanical character of faults found in the shallow crust.

Journal

Journal of Structural GeologyElsevier

Published: Nov 1, 1997

References

  • Permeability and frictional properties of San Andreas fault gouge
    Chu, C.L.; Wang, C.Y.
  • Groundwater flow systems in mountainous terrain 1
    Forster, C.B.; Smith, L.
  • Steady-state groundwater flow across idealized faults
    Haneberg, W.C.
  • Fluid flow in fault zones: Analysis of the interplay of convective circulation and topographically driven groundwater flow
    Lopez, D.L.; Smith, L.
  • Permeability of rock samples from Cajon Pass, California
    Morrow, C.A.; Byerlee, J.
  • Permeability differences between surface-derived and deep drillhole core samples
    Morrow, C.A.; Lockner, D.A.
  • Permeability and strength of San Andreas gouge under high pressure
    Morrow, C.A.; Shi, L.Q.; Byerlee, J.D.

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Search

Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly

Organize

Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.

Access

Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

DeepDyve

Freelancer

DeepDyve

Pro

Price

FREE

$49/month
$360/year

Save searches from
Google Scholar,
PubMed

Create folders to
organize your research

Export folders, citations

Read DeepDyve articles

Abstract access only

Unlimited access to over
18 million full-text articles

Print

20 pages / month

PDF Discount

20% off