Along-strike fault core thickness variations of a fault in poorly lithified sediments, Miri (Malaysia)

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Abstract

Fault resistance to across-fault fluid flow is as strong as its weakest point. Processes that determine patches of the fault surface containing transmissible fault rocks must be taken into account to produce reliable predictions of cross fault fluid flow. We use a study site in Miri as a natural laboratory to investigate in detail the fault core thickness variations along-strike and down dip and to quantify the risk of discontinuities in the clay-rich fault core.

Five fault core types have been identified: foliated clay-rich fault core, chaotic clay-rich fault core, attenuated clay-rich fault core, sandy anastomosing shears and sandy breccia. The sandy fault rocks are likely to have lower capillary entry pressure, and higher permeability than the clay-rich rock, so could represent potential cross-fault flow pathways.

We performed a geostatistical analysis, showing a correlation over 3 m scale, suggesting the presence of ‘patches’ of thin and thick fault core generally less than 3m in length. We interpret this as superimposition of two (or more) different deformation processes at a smaller and larger scale. We speculate on the processes that could produce the observed distribution of thickness and composition, in particular processes that could have disrupted the through-going clay-rich core.
Original languageEnglish
Pages (from-to)189-206
Number of pages18
JournalJournal of Structural Geology
Volume116
Early online date25 Aug 2018
DOIs
Publication statusPublished - 30 Nov 2018

Fingerprint

Sediments
Clay
sediment
Rocks
clay
Flow of fluids
fluid flow
rock
capillary pressure
Chemical analysis
breccia
fault plane
low pressure
dip
discontinuity
permeability

Keywords

  • fault core
  • clay smear
  • along-strike thickness
  • variogram

Cite this

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title = "Along-strike fault core thickness variations of a fault in poorly lithified sediments, Miri (Malaysia)",
abstract = "Fault resistance to across-fault fluid flow is as strong as its weakest point. Processes that determine patches of the fault surface containing transmissible fault rocks must be taken into account to produce reliable predictions of cross fault fluid flow. We use a study site in Miri as a natural laboratory to investigate in detail the fault core thickness variations along-strike and down dip and to quantify the risk of discontinuities in the clay-rich fault core.Five fault core types have been identified: foliated clay-rich fault core, chaotic clay-rich fault core, attenuated clay-rich fault core, sandy anastomosing shears and sandy breccia. The sandy fault rocks are likely to have lower capillary entry pressure, and higher permeability than the clay-rich rock, so could represent potential cross-fault flow pathways. We performed a geostatistical analysis, showing a correlation over 3 m scale, suggesting the presence of ‘patches’ of thin and thick fault core generally less than 3m in length. We interpret this as superimposition of two (or more) different deformation processes at a smaller and larger scale. We speculate on the processes that could produce the observed distribution of thickness and composition, in particular processes that could have disrupted the through-going clay-rich core.",
keywords = "fault core, clay smear, along-strike thickness, variogram",
author = "{Sosio De Rosa}, Silvia and Shipton, {Zoe K.} and Lunn, {Rebecca J.} and Yannick Kremer and Titus Murray",
year = "2018",
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AU - Sosio De Rosa, Silvia

AU - Shipton, Zoe K.

AU - Lunn, Rebecca J.

AU - Kremer, Yannick

AU - Murray, Titus

PY - 2018/11/30

Y1 - 2018/11/30

N2 - Fault resistance to across-fault fluid flow is as strong as its weakest point. Processes that determine patches of the fault surface containing transmissible fault rocks must be taken into account to produce reliable predictions of cross fault fluid flow. We use a study site in Miri as a natural laboratory to investigate in detail the fault core thickness variations along-strike and down dip and to quantify the risk of discontinuities in the clay-rich fault core.Five fault core types have been identified: foliated clay-rich fault core, chaotic clay-rich fault core, attenuated clay-rich fault core, sandy anastomosing shears and sandy breccia. The sandy fault rocks are likely to have lower capillary entry pressure, and higher permeability than the clay-rich rock, so could represent potential cross-fault flow pathways. We performed a geostatistical analysis, showing a correlation over 3 m scale, suggesting the presence of ‘patches’ of thin and thick fault core generally less than 3m in length. We interpret this as superimposition of two (or more) different deformation processes at a smaller and larger scale. We speculate on the processes that could produce the observed distribution of thickness and composition, in particular processes that could have disrupted the through-going clay-rich core.

AB - Fault resistance to across-fault fluid flow is as strong as its weakest point. Processes that determine patches of the fault surface containing transmissible fault rocks must be taken into account to produce reliable predictions of cross fault fluid flow. We use a study site in Miri as a natural laboratory to investigate in detail the fault core thickness variations along-strike and down dip and to quantify the risk of discontinuities in the clay-rich fault core.Five fault core types have been identified: foliated clay-rich fault core, chaotic clay-rich fault core, attenuated clay-rich fault core, sandy anastomosing shears and sandy breccia. The sandy fault rocks are likely to have lower capillary entry pressure, and higher permeability than the clay-rich rock, so could represent potential cross-fault flow pathways. We performed a geostatistical analysis, showing a correlation over 3 m scale, suggesting the presence of ‘patches’ of thin and thick fault core generally less than 3m in length. We interpret this as superimposition of two (or more) different deformation processes at a smaller and larger scale. We speculate on the processes that could produce the observed distribution of thickness and composition, in particular processes that could have disrupted the through-going clay-rich core.

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