Fault zone architecture and permeability structure
TL;DR: In this article, the authors developed qualitative and quantitative schemes for evaluating fault-related permeability structures by using results of field investigations, laboratory permeability measurements, and numerical models offlow within and near fault zones.
Abstract: Fault zone architecture and related permeability structures form primary controls on fluid flow in upper-crustal, brittle fault zones. We develop qualitative and quantitative schemes for evaluating fault-related permeability structures by using results of field investigations, laboratory permeability measurements, and numerical models offlow within andnearfaultzones.Thequalitativeschemecomparesthepercentageofthetotalfaultzone width composed of fault core materials (e.g., anastomosing slip surfaces, clay-rich gouge, cataclasite,andfaultbreccias)tothepercentageofsubsidiarydamagezonestructures(e.g., kinematically related fracture sets, small faults, and veins). A more quantitative scheme is developed to define a set of indices that characterize fault zone architecture and spatial variability.Thefaultcoreanddamagezonearedistinctstructuralandhydrogeologicunits that reflect the material properties and deformation conditions within a fault zone. Whether a fault zone will act as a conduit, barrier, or combined conduit-barrier system is controlled by the relative percentage of fault core and damage zone structures and the inherent variability in grain scale and fracture permeability. This paper outlines a frameworkforunderstanding,comparing,andcorrelatingthefluidflowpropertiesoffaultzones in various geologic settings.
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TL;DR: Fault zones and fault systems have a key role in the development of the Earth's crust and control the mechanics and fluid flow properties of the crust, and the architecture of sedimentary deposits in basins as discussed by the authors.
1,057 citations
Cites background from "Fault zone architecture and permeab..."
...In the original Caine et al. (1996) fault core and damage zone model of fault architecture the fault core was visualised as providing an across-fault barrier to flow and the fractured damage zone as an along/up-fault conduit....
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TL;DR: In this article, the authors use a geometric classification of damage zones into tip-, wall-, and linking-damage zones, based on their location around faults, which can be sub-divided in terms of fault and fracture patterns within the damage zone.
678 citations
Cites background from "Fault zone architecture and permeab..."
...Fault growth commonly produces a fault core composed of slip surfaces and comminuted rock material, and also a broader volume of distributed deformation called the damage zone (McGrath and Davison, 1995; Caine et al., 1996; Vermilye and Scholz, 1998, 1999)....
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TL;DR: In this article, the authors investigated the permeability structure of a fault zone in granitic rocks by laboratory testing of intact core samples from the unfaulted protolith and the two principal fault zone components; the fault core and damaged zone.
619 citations
TL;DR: Deformation bands are the most common strain localization feature found in deformed porous sandstones and sediments, including Quaternary deposits, soft gravity slides and tectonically affected sandstones in hydrocarbon reservoirs and aquifers as discussed by the authors.
Abstract: Deformation bands are the most common strain localization feature found in deformed porous sandstones and sediments, including Quaternary deposits, soft gravity slides and tectonically affected sandstones in hydrocarbon reservoirs and aquifers. They occur as various types of tabular deformation zones where grain reorganization occurs by grain sliding, rotation and/or fracture during overall dilation, shearing, and/or compaction. Deformation bands with a component of shear are most common and typically accommodate shear offsets of millimetres to centimetres. They can occur as single structures or cluster zones, and are the main deformation element of fault damage zones in porous rocks. Factors such as porosity, mineralogy, grain size and shape, lithification, state of stress and burial depth control the type of deformation band formed. Of the different types, phyllosilicate bands and most notably cataclastic deformation bands show the largest reduction in permeability, and thus have the greatest potential to influence fluid flow. Disaggregation bands, where non-cataclastic, granular flow is the dominant mechanism, show little influence on fluid flow unless assisted by chemical compaction or cementation.
589 citations
TL;DR: In this paper, the role of structural heterogeneity in hydrocarbon entrapment, migration and flow is discussed and three common structural heterogeneity types are considered: dilatant fractures (joints, veins, and dikes); contraction/compaction structures (solution seams and compaction bands); and shear fractures (faults).
560 citations
References
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25 Jan 1991TL;DR: The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws -producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events.
Abstract: This essential reference for graduate students and researchers provides a unified treatment of earthquakes and faulting as two aspects of brittle tectonics at different timescales. The intimate connection between the two is manifested in their scaling laws and populations, which evolve from fracture growth and interactions between fractures. The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws - producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events. The third edition of this classic treatise presents a wealth of new topics and new observations. These include slow earthquake phenomena; friction of phyllosilicates, and at high sliding velocities; fault structures; relative roles of strong and seismogenic versus weak and creeping faults; dynamic triggering of earthquakes; oceanic earthquakes; megathrust earthquakes in subduction zones; deep earthquakes; and new observations of earthquake precursory phenomena.
3,802 citations
"Fault zone architecture and permeab..." refers background in this paper
...They may act as conduits, barriers, or combined conduitbarrier systems that enhance or impede fluid flow (Randolph and Johnson, 1989; Smith et al., 1990; Scholz, 1990; Caine et al., 1993; Forster et al., 1994; Antonellini and Aydin, 1994; Newman and Mitra, 1994; Goddard and Evans, 1995)....
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TL;DR: In this article, the internal structure of the San Gabriel fault and the Punchbowl fault are combined with previous characterizations of the SGF and PF to evaluate possible explanations for the low frictional strength and seismic characteristics.
Abstract: New observations of the internal structure of the San Gabriel fault (SGF) are combined with previous characterizations of the Punchbowl fault (PF) to evaluate possible explanations for the low frictional strength and seismic characteristics of the San Andreas fault (SAF). The SGF and PF are ancient, large-displacement faults of the SAF system exhumed to depths of 2 to 5 km. These fault zones are internally zoned; the majority of slip was confined to the cores of principal faults, which typically consist of a narrow layer (less than tens of centimeters) of ultracataclasite within a zone of foliated cataclasite several meters thick. Each fault core is bounded by a zone of damaged host rock of the order of 100 m thick. Orientations of subsidiary faults and other fabric elements imply that (1) the maximum principal stress was oriented at large angles to principal fault planes, (2) strain was partitioned between simple shear in the fault cores and nearly fault-normal contraction in the damaged zones and surrounding host rock, and (3) the principal faults were weak. Microstructures and particle size distributions in the damaged zone of the SGF imply deformation was almost entirely cataclastic and can be modeled as constrained comminution. In contrast, cataclastic and fluid-assisted processes were significant in the cores of the faults as shown by pervasive syntectonic alteration of the host rock minerals to zeolites and clays and by folded, sheared, and attenuated cross-cutting veins of laumontite, albite, quartz, and calcite. Total volume of veins and neocrystallized material reaches 50% in the fault core, and vein structure implies episodic fracture and sealing with time-varying and anisotropic permeability in the fault zone. The structure of the ultracataclasite layer reflects extreme slip localization and probably repeated reworking by particulate flow at low effective stresses. The extreme slip localization reflects a mature internal fault structure resulting from a positive feedback between comminution and transformation weakening. The structural, mechanical, and hydrologic characteristics of the Punchbowl and San Gabriel faults support the model for a weak San Andreas based on inhomogeneous stress and elevated pore fluid pressures contained within the core of a seismogenic fault. Elevated fluid pressures could be repeatedly generated in the core of the fault by a combination of processes including coseismic dilatancy and creation of fracture permeability, fault-valve behavior to recharge the fault with fluid, post-seismic self-sealing of fracture networks to reduce permeability and trap fluids, and time-dependent compaction of the core to generate high pore pressure. The localized slip and fluid-saturated conditions are wholly compatible with additional dynamic weakening by thermal pressurization of fluids during large seismic slip events, which can help explain both the low average strength of the San Andreas and seismogenic characteristics such as large stress relief. In addition, such a dynamic weakening mechanism is expected only in mature fault zones and thus could help explain the apparent difference in strength of large-displacement faults from smaller-displacement, subsidiary seismogenic faults.
937 citations
"Fault zone architecture and permeab..." refers background in this paper
...Fracture density in the fault core is usually significantly less than in the damage zone (Andersson et al., 1991; Chester et al., 1993)....
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TL;DR: The thrust sheet acts like a great squeegee, driving fluids ahead of it and producing widespread geologic consequences such as faulting, magma generation, migration of hydrocarbons, transport of minerals, metamorphism, and paleomagnetism as discussed by the authors.
Abstract: This paper presents and supports a speculative hypothesis, the essence of which follows. When continental margins in zones of convergence are buried beneath thrust sheets, fluids expelled from the margin sediments travel into the foreland basin and the continental interior. These tectonic fluids have key roles in phenomena such as faulting, magma generation, migration of hydrocarbons, transport of minerals, metamorphism, and paleomagnetism. The thrust sheet, crudely speaking, acts like a great squeegee, driving fluids ahead of it and producing widespread geologic consequences.
750 citations
"Fault zone architecture and permeab..." refers methods in this paper
...The schemes are based on a synopsis of our research and the work of other authors (Sibson, 1981; Oliver, 1986; Chester and Logan, 1986; Parry and Bruhn, 1986; Scholz, 1987; Scholz and Anders, 1994; Parry et al., 1988; Bruhn et al., 1990; Smith et al., 1990; Forster and Evans, 1991; Moore and…...
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TL;DR: In this article, the authors quantified fault zone permeability in outcrop by detailed geologic mapping and by measurements using a minipermeameter, and found that deformation bands have porosity about one order of magnitude less than the surrounding host rock.
Abstract: Fault zone permeability in outcrop is quantified by detailed geologic mapping and by measurements using a minipermeameter. Deformation bands, zones of deformation bands, and slip planes are structural elements associated with successive stages in the evolution of a fault zone in porous sandstones. Deformation bands have a porosity about one order of magnitude less than the surrounding host rock and, on average, a permeability three orders of magnitude less than the surrounding host rock. The intensity of cataclasis and the clay content control the amount of permeability reduction as measured perpendicular to a band. The wall rock in proximity to slip planes can have permeabilities more than seven orders of magnitude less than the pristine sandstone. Capillary pressure wit in deformation bands is estimated to be 10-100 times larger than that in the surrounding host rock. Thus, deformation bands and slip planes can substantially modify fluid flow properties of a reservoir and have potential sealing capabilities with respect to a nonwetting phase, as evident in outcrop exposure.
595 citations
"Fault zone architecture and permeab..." refers background in this paper
...They may act as conduits, barriers, or combined conduitbarrier systems that enhance or impede fluid flow (Randolph and Johnson, 1989; Smith et al., 1990; Scholz, 1990; Caine et al., 1993; Forster et al., 1994; Antonellini and Aydin, 1994; Newman and Mitra, 1994; Goddard and Evans, 1995)....
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...Grain-size reduction and/or mineral precipitation generally yield fault cores with lower porosity and permeability than the adjacent protolith (e.g., Chester and Logan, 1986; Antonellini and Aydin, 1994; Goddard and Evans, 1995)....
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TL;DR: In this paper, the authors use Darcy's law to model fluid flow from accretionary prisms with matrix and fracture percolation, and assign different permeabilities to the matrix and fractures.
Abstract: Accretionary prisms are composed of initially saturated sediments caught in subduction zone tectonism. As sediments deform, fluid pressures rise and fluid is expelled, resembling a saturated sponge being tectonically squeezed. Fluid flow from the accretionary prism feeds surface biological cases, precipitates and dissolves minerals, and causes temperature and geochemical anomalies. Structural and metamorphic features are affected at all scales by fluid pressures or fluid flow in accretionary prisms. Accordingly, this dynamic tectonic environment provides an accessible model for fluid/rock interactions occurring at greater crustal depths. Porosity reduction and to a lesser degree mineral dehydration and the breakdown of sedimentary organic matter provide the fluids expelled from accretionary prisms. Mature hydrocarbons expulsed along prism faults indicate deep sources and many tens of kilometers of lateral transport of fluids. Many faults cutting accretionary prisms expel fluids fresher than seawater, presumably generated by dehydration of clay minerals at depth. Models of fluid flow from accretionary prisms use Darcy's law with matrix and fractures/faults being assigned different permeabilities. Fluid pressures in accretionary prisms are commonly high but range from hydrostatic to lithostatic. Matrix or intergranular permeability ranges from less than 10−20 m² to 10−13 m². Fracture permeability probably exceeds 10−12 m². A global estimate of fluid flux into accretionary prisms suggests they recycle the oceans every 500 m.y. Fluid flow out of accretionary prisms occurs by distributed flow through intergranular permeability and along zones of focused flow, typically faults. Focused fluid flow is 3 to 4 orders of magnitude faster than distributed flow, probably representing the mean differences in permeability along these respective expulsion paths. During the geological evolution of accretionary prisms, distributed flow through pore spaces decreases as a result of consolidation and cementation, whereas flow along fracture systems becomes dominant. Although thrust faults are most common in the compressional environment of accretionary prisms, normal and strike-slip faults are efficient fluid drains, because they are easier to dilate. Observations from both modern and ancient prisms suggest episodic fluid flow which is probably coupled to episodic fault displacement and ultimately to the earthquake cycle.
551 citations
"Fault zone architecture and permeab..." refers background in this paper
...…(Sibson, 1981; Oliver, 1986; Chester and Logan, 1986; Parry and Bruhn, 1986; Scholz, 1987; Scholz and Anders, 1994; Parry et al., 1988; Bruhn et al., 1990; Smith et al., 1990; Forster and Evans, 1991; Moore and Vrolijk, 1992; Caine et al., 1993; Newman and Mitra, 1994; Goddard and Evans, 1995)....
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...Each of the four end-member architectural styles is associated with a characteristic permeability structure (Chester and Logan, 1986; Bruhn et al., 1990; Forster and Evans, 1991; Moore and Vrolijk, 1992; Newman and Mitra, 1994)....
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