Fracture attributes in reservoir-scale carbonate fault damage zones and implications for damage zone width and growth in the deep subsurface

AbstractDamage zones of different fault types are investigated in siliciclastics (Utah, USA), carbonates (Majella Mountain, Italy) and metamorphic rocks (western Norway). The study was conducted taking measurements of deformation features such as fractures and deformation bands on multiple 1D scanlines along fault walls. The resulting datasets are used to plot the frequency distribution of deformation features and to constrain the geometrical width of the damage zone for the studied faults. The damage-zone width of a single fault is constrained by identifying the changes in the slope of cumulative plots made on the frequency data. The cumulative plot further shows high deformation frequency by a steep slope (inner damage zone) and less deformation as a gentle slope (outer damage zone). Statistical distributions of displacement and damage-zone width and their relationship are improved, and show two-slope power-law distributions with a break point at c. 100 m displacement. Bleached sandstones in the studied siliciclastic rocks of Utah are associated with a higher frequency of deformation bands and a wider damage zone compared to the unbleached zone of similar lithology. Fault damage zones in the carbonate rocks of Majella are often host to open fractures (karst), demonstrating that they can also be conductive to fluid flow.

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Seismic imaging of fault damaged zone and its scaling relation with displacement

Interpretation ◽

10.1190/int-2016-0230.1 ◽

2017 ◽

Vol 5 (4) ◽

pp. SP83-SP93 ◽

Cited By ~ 3

Author(s):

Behzad Alaei ◽

Anita Torabi

Keyword(s):

Seismic Data ◽

Process Zone ◽

Damage Zone ◽

Frequency Resolution ◽

Segment Length ◽

Time Frequency ◽

Zone Width ◽

Damaged Zone ◽

Fault Bend ◽

Different Depths

We have studied seismically resolved damaged zone of normal faults in siliciclastic rocks of the Norwegian continental shelf. The workflow we have developed reveals structural details of the fault damaged zone and in particular, the subsidiary synthetic faults, horsetail at the main lateral fault tips at different depths and fault bend. These subsidiary or small fault segments form an area that can be clearly followed laterally and vertically. We call this area fault damaged zone. The studied damaged zone on seismic data comprises the fault core and the fault damage zone, as defined in outcrop studies. Spectral decomposition (short-time Fourier transform for time-frequency resolution and continuous wavelet transform) was performed on the data centered around faulted intervals. The magnitude of higher frequencies was used to generate coherence attribute volumes. Coherence attributes were filtered to enhance fault images. This integrated workflow improves fault images on reflection seismic data. Our approach reveals details of damaged zone geometry and morphology, which are comparable with the outcrop studies of similar examples conducted by previous researchers or us. We have extracted the fault geometry data including the segment length, displacement, and damaged zone width at different depths. Our results show that subsidiary faults, fault bends, linkage of fault segments, and branching in the fault tip (horsetail structure or process zone) all affect the width of the damaged zone and the distribution of displacement. We have seen a distinct increase in the fault damaged zone width near the fault bend locations. The fault segment length decreases with depth toward the lower fault tip, which is below the base Cretaceous unconformity. In addition, the displacement increases below the unconformity. In general, there is a positive correlation between fault displacement and the corresponding damaged zone width measured in this study, which is in agreement with previous studies.

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Stratigraphic control on damage zone width in faulted platform carbonates: an example from the Gozo Island, Malta

10.5194/egusphere-egu2020-9747 ◽

2020 ◽

Author(s):

Mattia Martinelli ◽

Andrea Bistaccchi ◽

Riccardo Castellanza

Keyword(s):

Damage Zone ◽

Ore Deposits ◽

Triaxial Tests ◽

Normal Faults ◽

Published Data ◽

Fault Mechanics ◽

Zone Width ◽

Mechanical Stratigraphy ◽

Study Results ◽

Platform Carbonates

Fault damage zones (DZ) are fractured volumes of rock that surround the fault core(s), and their structure can have an important role on the control of fault mechanics and of the hydraulic properties of the fault zone, with impact on groundwater flow, ore-deposits, hydrocarbon reservoirs, nuclear waste disposal and contaminant transport in the subsurface. It is generally accepted that DZ width is controlled by fault displacement, and that it increases with increasing offset. However, published data on DZ width in faulted carbonates show a scattering over two orders of magnitude, suggesting that this parameter is controlled also by other factors. Here we present the results of a study performed on two units of the platform carbonates of the Malta and Gozo Islands. These two units, that are cross-cut by normal faults, are characterize by different petrographical, petrophysical and mechanical properties and have completely different Damage Zone width along faults characterized by the same tectonic history and with comparable displacement. More competent and rigid grain-dominated carbonates show DZ thickness of several hundreds of meters, while fracturing in the less competent and more elastic micrite-dominated rocks is developed only very close to the fault core, with a DZ width of few tens of meters. In order to explain this counterintuitive facies-controlled behavior, we performed petrophysical (porosity, density, permeability) and geo-mechanical (Uniaxial, Brazilian, Triaxial tests) analyses to characterize the mechanical stratigraphy and develop a numerical modelling study. Results highlight the heterogeneous stress distribution in a multilayer with variable elastic parameters subjected to horizontal extension. The more elastic unit can more easily expand laterally with respect to the less elastic one with the consequence that &#963;3 decrease faster in the last one and this can yield before the more compliant one even if it is stronger. Also the width of the yielding zone is increased in the stiffer layers, leading to a wider DZ.

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Defining the relationship between fault throw and fault damage zone width from seismic data by utilising seismic attributes.

Proc of Indonesian Petroleum Association 42nd Annual Convention ◽

10.29118/ipa18.67.g ◽

2018 ◽

Author(s):

C. Sirait

Keyword(s):

Seismic Data ◽

Damage Zone ◽

Seismic Attributes ◽

Zone Width ◽

Fault Damage Zone ◽

The Relationship

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The effect of geometrical irregularities on damage zone width: Modeling and field observations

10.5194/egusphere-egu2020-5884 ◽

2020 ◽

Author(s):

Yuval Tal ◽

Daniel Faulkner

Keyword(s):

Inelastic Deformation ◽

Field Data ◽

Damage Zone ◽

Fault Zones ◽

Small Displacement ◽

Field Observations ◽

Zone Width ◽

Wide Range ◽

Fracture Damage ◽

Observed Damage

Geological and geophysical observations of fault zones reveal that fault cores are surrounded by regions of damaged rocks consist of fractures at a wide range of length scales with decaying intensity with distance from the fault core. The main mechanisms proposed for the development of off-fault damage include slip on faults with geometrical irregularities, migrating process zones, and dynamic damage from the passage of earthquake ruptures. Field observations of relatively deep exhumed fault zones have shown that fault damage zone width scales with the displacement on a fault. In this study, we combine such observations with numerical modeling to test what is the dominant mechanism producing off-fault damage at depth of several kilometres.The field data [Faulkner et al., 2011] include measurements of micro-fracture damage zone width from small displacement fault zones within the Atacama fault zone in northern Chile that formed at &#8764;6 km depth within a dioritic protolith. An increase in damage zone width with displacement is clearly seen. We perform simulations of slip on synthetic faults, with roughness properties similar to that of natural faults, and examine how the total slip and roughness characteristics affect the extent and intensity of inelastic deformation to constrain the geometrical and frictional properties that could generate the observed damage. To accurately account for the effects of geometrical irregularities on the fault and allow slip that is large relative to the size the minimum roughness wavelength, we use the mortar finite element method, in which non-matching meshes are allowed across the fault and the contacts are continuously updated. Inelastic deformation of the bulk is modelled with Drucker&#8211;Prager viscoplasticity, which is a simple choice for describing cracked medium and is closely related to the Mohr&#8211;Coulomb model. Our results indicate that, for the depth and fault lengths in the field data, geometrical irregularities produce the scaling of damage zone width with displacement observed in the field and suggest that this, rather than the other mechanisms, produce most of the damage.

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