Permeability of carbonate fault rocks: a case study from Malta

2019 ◽  
Vol 26 (3) ◽  
pp. 418-433 ◽  
Author(s):  
Andy P. Cooke ◽  
Quentin J. Fisher ◽  
Emma A. H. Michie ◽  
Graham Yielding
Keyword(s):  
Fluid Flow ◽  
Host Rock ◽  
Damage Zone ◽  
Fault Zones ◽  
High Porosity ◽  
Rock Permeability ◽  
Fault Rock ◽  
Fault Rocks ◽  
Diagenetic Alteration ◽  
Hydraulic Behaviour

The inherent heterogeneity of carbonate rocks suggests that carbonate-hosted fault zones are also likely to be heterogeneous. Coupled with a lack of host–fault petrophysical relationships, this makes the hydraulic behaviour of carbonate-hosted fault zones difficult to predict. Here we investigate the link between host rock and fault rock porosity, permeability and texture, by presenting data from series of host rock, damage zone and fault rock samples from normally faulted, shallowly buried limestones from Malta. Core plug X-ray tomography indicates that texturally heterogeneous host rocks lead to greater variability in the porosity and permeability of fault rocks. Fault rocks derived from moderate- to high-porosity (>20%) formations experience permeability reductions of up to six orders of magnitude relative to the host; >30% of these fault rocks could act as baffles or barriers to fluid flow over production timescales. Fault rocks derived from lower-porosity (<20%) algal packstones have permeabilities that are lower than their hosts by up to three orders of magnitude, which is unlikely to impact fluid flow on production timescales. The variability of fault rock permeability is controlled by a number of factors, including the initial host rock texture and porosity, the magnitude of strain localization, and the extent of post-deformation diagenetic alteration. Fault displacement has no obvious control over fault rock permeability. The results enable better predictions of fault rock permeability in similar lithotypes and tectonic regimes. This may enable predictions of across-fault fluid flow potential when combined with data on fault zone architecture.

scholarly journals Petrophysical Properties and Microstructural Analysis of Faulted Heterolithic Packages: A Case Study from Miocene Turbidite Successions, Italy

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-23 ◽  
Author(s):  
Hannah Riegel ◽  
Miller Zambrano ◽  
Fabrizio Balsamo ◽  
Luca Mattioni ◽  
Emanuele Tondi
Keyword(s):  
Fluid Flow ◽  
Host Rock ◽  
Damage Zone ◽  
Microstructural Analysis ◽  
Fault Zones ◽  
Clay Material ◽  
Fault Rock ◽  
Matrix Permeability ◽  
The Matrix ◽  
The Individual

Geofluid reservoirs located in heterolithic successions (e.g., turbidites) can be affected by vertical and lateral compartmentalization due to interbedded fine-grained facies (i.e., shale, siltstones) and the presence of faults, respectively. A fault can behave as a conduit or barrier to fluid flow depending on its architecture and the individual hydraulic behavior of its components (i.e., fault core, damage zone). The fault core, normally composed by fault rock or smeared clay material, commonly acts as a flow inhibitor across the fault. Fault-related fractures (macro- and microscopic) in the damage zone generally increase the permeability parallel to the fault, except when they are cemented or filled with gouge material. Although macrofractures (which define the fracture porosity) dominate fluid flow, the matrix porosity (including microfractures) begins to have a more important role in fluid flow as the aperture of macrofractures is occluded, particularly at greater depth. This study investigates the variation in matrix permeability in fault zones hosted in heterolithic successions due to fault architecture and stratigraphy of host rock (i.e., sand-rich turbidites). Two key areas of well-exposed, faulted Miocene turbidites located in central and southern Italy were selected. For this study, six separate fault zones of varying offset were chosen. Each impacts heterolithic successions that formed under similar tectonic conditions and burial depths. Across the selected fault zones, an extensive petrophysical analysis was done in the field and laboratory, through air permeameter measurements, thin section, and synchrotron analysis in both host rock, damage zone, and fault core. Results suggest that the amount and distribution of clay layers in a heterolithic sequence affects fluid flow across the fault, regardless of fault offset.

Periodic Fluid-mediated Weakening and Cementation Drives Cyclic Reorganisation of Shallow Basaltic Fault Zones

2021 ◽  
Author(s):  
Bob Bamberg ◽  
Richard Walker ◽  
Marc Reichow
Keyword(s):  
Host Rock ◽  
Slip Surface ◽  
Damage Zone ◽  
Fluid Pressure ◽  
Fault Zones ◽  
Fault Activity ◽  
Cyclic Activity ◽  
Fault Rock ◽  
Vein Formation ◽  
Rock Mechanical Properties

&lt;p&gt;Faults constitute the major source for mechanical and permeability heterogeneity in basaltic sequences, yet their architecture, and mechanical and physical properties remain poorly understood. These are however critical as basaltic reservoirs are becoming increasingly important for geothermal applications and CO&lt;sub&gt;2&lt;/sub&gt; storage. Here we present a detailed microstructural- to outcrop-scale characterisation of mature (decametre-hectometre displacement) fault zones in layered basalts, in the Faroe Islands. Outcrop scale structures and fault rock distribution within the fault zone were mapped in the field to build 3D virtual outcrop models, with detailed characterisation of fault rock microstructure and petrology obtained from optical and SE-microscopy.&lt;/p&gt;&lt;p&gt;The fault zones exhibit evidence for cyclic activity controlled by fault internal fluid pressure variation. Deformation mechanisms in the core alternate between shear-compaction, evidenced by foliated cataclasite and gouge development, and dilatation through fluid overpressure, leading to hydrofracture and vein formation. Generally, a decametre-wide damage zone of Riedel faults is centrally transected by the fault core. The fault core is organised around a principal slip surface (PSS) hosted in a decimetre-wide principal slip zone (PSZ). The PSS and PSZ are dominantly composed of (ultra-) cataclasites, while the remaining core comprises anastomosing cataclastic bands bounding lenticular zones of various brecciated fault rocks. Further, PSS-proximal zones show significant late-stage dilatation by hydrothermal breccias or tabular veins with up to decimetre apertures, filled with early syntaxial to blocky zeolite and/or late coarse (&amp;#8804; 1&amp;#160;cm) blocky calcite. The structures in the fault core are mutually overprinting, evidencing pulsed fault activity and PSS migration. The native plagioclase-pyroxene assemblage of the host rock is almost completely altered to zeolites and red-brown smectites in the fault core and along surrounding damage of mature faults, while lower displacement faults preserve the host rock mineralogy even in gouge. We infer that fluid flow along initial damage promotes alteration and the associated chemical weakening localises strain into a narrow PSZ. Here, fault activity is governed by alternating deformation styles &amp;#8211; shear&amp;#8209;compaction and dilatation &amp;#8211; suggesting changes in deformation mechanism linked to transient permeability decrease within the PSZ, followed by fluid overpressure and hydrofracture. Overall rock mechanical properties are thus governed by the combined effects of permanent chemical weakening and transient fluid-mediated mechanical weakening, alternating with cementation and healing, and will be explored by direct shear deformation experiments in the future.&lt;/p&gt;

scholarly journals Key controls on the hydraulic properties of fault rocks in carbonates

2020 ◽  
pp. petgeo2020-034
Author(s):  
E. A. H. Michie ◽  
A. P. Cooke ◽  
I. Kaminskaite ◽  
J. C. Stead ◽  
G. E. Plenderleith ◽  
...  
Keyword(s):  
Carbonate Reservoirs ◽  
Rock Properties ◽  
Burial Depth ◽  
Extrinsic Factors ◽  
Fault Rock ◽  
Fault Rocks ◽  
Content Type ◽  
Intrinsic Factors ◽  
Hydraulic Behaviour ◽  
Porosity And Permeability

A significant knowledge gap exists when analysing and predicting the hydraulic behaviour of faults within carbonate reservoirs. To improve this, a large database of carbonate fault rock properties has been collected from 42 exposed faults, from seven countries. Faults analysed cut a range of lithofacies, tectonic histories, burial depths and displacements. Porosity and permeability measurements from c. 400 samples have been made, with the goal of identifying key controls on the flow properties of fault rocks in carbonates. Intrinsic and extrinsic factors have been examined, such as host lithofacies, juxtaposition, host porosity and permeability, tectonic regime, displacement, and maximum burial depth, as well as the depth at the time of faulting. The results indicate which factors may have had the most significant influence on fault rock permeability, improving our ability to predict the sealing or baffle behaviour of faults in carbonate reservoirs. Intrinsic factors, such as host porosity, permeability and texture, appear to play the most important role in fault rock development. Extrinsic factors, such as displacement and kinematics, have shown lesser or, in some instances, a negligible control on fault rock development. This conclusion is, however, subject to two research limitations: lack of sufficient data from similar lithofacies at different displacements, and a low number of samples from thrust regimes.Thematic collection: This article is part of the Fault and top seals collection available at: https://www.lyellcollection.org/cc/fault-and-top-seals-2019

Thermophysical reservoir properties of the Hauptdolomit-facies underneath the Viennese basin across fault zones analogues – a reservoir study for the GeoTief EXPLORE project

2020 ◽  
Author(s):  
Doris Rupprecht ◽  
Sven Fuchs ◽  
Andrea Förster ◽  
Mariella Penz-Wolfmayr
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Fractured Rocks ◽  
Damage Zone ◽  
Fault Zones ◽  
Rock Properties ◽  
Zone Model ◽  
Geothermal Resources ◽  
Fault Rocks ◽  
The Impact

&lt;p&gt;The GeoTief EXPLORE project aims to explore the geothermal potential and quantify the geothermal resources of the Vienna Basin (Austria) and the underlying Northern Calcareous Alpine basement. The main target of geothermal interest is the massive and tectonically remolded Hauptdolomite facies that has been identified as potential geothermal reservoir in previous studies. Now, this formation is studied using outcrop analogues for the investigation of their petrophysical characterization and specific thermal properties (thermal conductivity and thermal diffusivity).&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Here, we report new measurements on a total of 60 samples from 6 outcrops in and around the area of Vienna applying different methods for the laboratory measurement of thermal and hydraulic rock properties. The petrophysical analysis considers the impact of deformation along and across fault zones, which introduces heterogeneity of storage properties and consequently in the thermophysical properties. Using the standard fault core and damage zone model, outcrop samples were grouped into unfractured and fractured protoliths, as well as in fault rocks, like breccias and cataclasites. Rock samples are then classified by their fracture density (m&amp;#178; fracture surface per m&amp;#179; rock) and by their matrix content and differences in grain sizes, respectively.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;The measured thermal rock properties vary significantly between the selected rock groups. The total range [90 % of values] is between 3.2 and 5.0 W/(mK) for thermal conductivity and between 1.3 and 2.7 mm&amp;#178;/s for thermal diffusivity. The results generally met the expected trend for fractured rocks as conductivity and diffusivity decreases with increasing porosity under unsaturated and saturated conditions. The total porosities are less than 5%. The variability of thermal conductivity under saturated conditions shows complex trends depending on the different rock classifications where fault rocks and highly fractured rocks of the damage zone show lower increase in thermal conductivities.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;The new petrophysical characterization will be the base for further numerical investigations of the hydraulic and thermal regime as well as for the analysis of the geothermal resources of the Hauptdolomite.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

On the straight and narrow: extreme localization of brittle fault damage and displacement along the Glade Fault Zone, Eastern Fiordland, New Zealand

2020 ◽  
Author(s):  
Michael Ofman ◽  
Steven Smith
Keyword(s):  
New Zealand ◽  
Fault Zone ◽  
Damage Zone ◽  
Shear Zones ◽  
Strike Slip ◽  
Fault Rock ◽  
Fault Rocks ◽  
X Ray ◽  
Fracture Damage ◽  
Host Rocks

&lt;p&gt;The southern Glade Fault Zone is a crustal-scale, subvertical dextral strike-slip fault zone on the eastern margin of Fiordland, New Zealand. For a distance of c. 40 km between Lake Te Anau and the Hollyford Valley, the fault cuts plutonic host rocks and has an estimated total dextral separation of c. 6-8 km. We report previously unidentified mylonites, cataclasites, pseudotachylites and fault gouge subparallel to pervasive sets of planar cooling joints in the Hut Creek-Mistake Creek area plutonic suites. The outcropping assemblage of joints and fault rocks record thermal, seismic and rheological conditions in the southern Glade Fault. Here we integrate methods to characterise the fault rocks and fracture damage zone of the southern Glade Fault from Glade Pass to Mt Aragorn. We use (i) EDS (Energy Dispersive x-ray Spectroscopy), XRD (X-Ray Diffraction) and EBSD (Electron Backscatter Diffraction) analysis to describe the mineralogy, kinematics and microstructures of fault rocks and, (ii) drone orthophotography and traditional structural measurements to detail geometrical relationships between structural features. Field mapping of glacially polished outcrops identifies the zone of brittle fault-related damage (i.e. damage zone + fault rock sequence) is up to one order of magnitude narrower than documented along other strike-slip faults with similar displacements, suggesting that the Glade Fault Zone represents an &amp;#8220;end-member&amp;#8221; of extreme localization of brittle deformation and fault displacement. This is interpreted to result from linkage of pre-existing cooling joints (and mylonitic shear zones), which allowed the younger brittle fault zone to establish its length and planarity relatively efficiently compared to the case of fault nucleation and growth in more isotropic host rocks.&lt;/p&gt;

scholarly journals Determination of the Youngest Active Domain in Major Fault Zones Using Medical X-ray Computed Tomography-derived Density Estimations

2021 ◽  
Author(s):  
akiyuki iwamori ◽  
Hideo Takagi ◽  
Nobutaka Asahi ◽  
Tatsuji Sugimori ◽  
Eiji Nakata ◽  
...  
Keyword(s):  
Fault Zone ◽  
Atomic Number ◽  
Density Ratio ◽  
Effective Atomic Number ◽  
Fault Zones ◽  
Ct Number ◽  
Fault Rock ◽  
Fault Rocks ◽  
X Ray Computed

Abstract Determination of the youngest active domains in fault zones that are not overlain by Quaternary sedimentary cover are critical for evaluating recent fault activity, determining the current local stress field, and mitigating the impacts of future earthquakes. Considering the exhumation of a fault zone, the youngest active domain in a fault zone is supposed to correspond to the activity at the minimum fault depth of a buried fault, such that the most vulnerable area, which possesses the lowest rock/protolith density ratio, is assumed to be indicative of this recent fault activity. However, it is difficult to measure the density of fault rocks and map the rock/protolith density ratio across a given fault zone. Here we utilize medical X-ray computed tomography (CT), a non-destructive technique for observing and analyzing materials, to investigate the fault characteristics of several fault zones and their surrounding regions in Japan, and attempt to determine the youngest active domain of a given fault zone based on its CT numbers, which are a function of the density and effective atomic number of the fault rock and protolith. We first investigate the density, void ratio, and effective atomic number of active and inactive fault rocks, and their respective protoliths. We then calculate the CT numbers after reducing the beam-hardening effects on the rock samples, and study the relationships among the CT number, density, and effective atomic number. We demonstrate that the density, effective atomic number, and CT number of the fault rock decrease as the youngest active zone is approached, such that the region with the lowest CT number and rock/protolith density ratio defines the youngest active domain of a given fault zone.

scholarly journals Carbonate clumped isotope thermometry of fault rocks and its possibilities: tectonic implications from calcites within Himalayan Frontal Fold-Thrust Belt

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Dyuti Prakash Sarkar ◽  
Jun-ichi Ando ◽  
Akihiro Kano ◽  
Hirokazu Kato ◽  
Gautam Ghosh ◽  
...  
Keyword(s):  
Fault Zone ◽  
Analytical Techniques ◽  
Fault Zones ◽  
Low Grade ◽  
Fault Rock ◽  
Fault Rocks ◽  
Main Boundary Thrust ◽  
Element Partitioning ◽  
Clumped Isotope ◽  
Northwest India

AbstractDisentangling the temperature and depth of formation of fault rocks is critical for understanding their rheology, exhumation, and the evolution of fault zones. Estimation of fault rock temperatures mostly relies on conventional geothermometers of metamorphic minerals and element partitioning analysis, which are largely inapplicable in shallow crustal fault rocks. Here, we demonstrate the applicability of the carbonate clumped isotope thermometer in low-grade carbonate-bearing fault rocks from the Himalayan frontal wedge (northwest India). Coalescing carbonate clumped isotope thermometry and calcite e-twin morphology allows us to constrain the temperature and depth of formation of the two main thrusts of the Himalayan frontal wedge, the Nahan thrust (170 ± 10 °C; 6–7 km depth), and the Main Boundary thrust (262 ± 30 °C; 10–11 km depth). The integration of the adopted analytical techniques can promote the application of calcite-based clumped isotope thermometry to the fault zone processes and refinement of shallow crustal fault zone models.

Magnetic fabric in brittle faults and ductile shear-zones: Examples from cataclasites from the Iberian Peninsula

2020 ◽  
Author(s):  
Marcos Marcén ◽  
Antonio Casas-Sainz ◽  
Teresa Román-Berdiel ◽  
Belén Oliva-Urcia ◽  
Ruth Soto ◽  
...  
Keyword(s):  
Shear Zones ◽  
Fault Zones ◽  
Magnetic Fabric ◽  
Fault Rock ◽  
Fault Rocks ◽  
Magnetic Lineation ◽  
Magnetic Fabrics ◽  
Transport Direction ◽  
Wide Range ◽  
Magnetic Lineations

&lt;p&gt;Shear zones, or their counterparts in near-surface conditions, the brittle fault zones, constitute crustal-scale, narrow, planar domains where deformation is strongly localized. The variation with depth of deformation conditions (P-T), rheology and strain rates entails a wide range of fault rock types, characterized by different petrofabrics and classically grouped into mylonitic (fault rocks undergoing crystalline plasticity) and cataclasitic (fault rocks undergoing frictional deformation) series. Magnetic fabric methods (most frequently anisotropy of magnetic susceptibility, AMS) have been established as a useful tool to determine fault rock petrofabrics in shear/fault zones, being interpreted as kinematic indicators with a considerable degree of success. However, mylonites and cataclasites show remarkable differences in magnetic carriers, shape and orientation of the fabric ellipsoid. Here, we present a study of ten brittle fault zones (one of them at the plastic-brittle transition) located in various locations in the Iberian Plate, with an aim &amp;#160;to interpret patterns of AMS in cataclasites.&lt;/p&gt;&lt;p&gt;Reviewing AMS studies dealing with SC mylonites, three fundamental features can be drawn: i) the presence of composite magnetic fabrics with shape and lattice-preferred orientations, ii) the fabric is carried predominately by ferromagnetic minerals and iii) surprisingly in composite fabrics, the absolute predominance of magnetic lineations parallel to (shear) transport direction (88% of the reviewed sites), independently of fabrics being defined by paramagnetic or ferromagnetic carriers. Based on our study, magnetic fabrics in cataclasites: i) are mainly carried by paramagnetic minerals and ii) show a strong variability in magnetic lineation orientations, which in relation with SC deformational structures, are either parallel to transport direction (44% of sites) or parallel to the intersection lineation between shear (C) and foliation (S) planes (41%). Furthermore, changes between the two end-members can be frequently observed in the same fault zone. Sub-fabric determinations (LT-AMS; AIRM and AARM) also indicate that the type of magnetic lineation cannot be consistently related with a specific mineralogy (i.e. paramagnetic vs ferromagnetic minerals).&lt;/p&gt;&lt;p&gt;The wide range of deformation conditions and fault rocks covered in our study allowed us to analyse the factors that control these different magnetic lineation orientations, especially in brittle contexts. Plastic deformation results into a mineral stretching parallel to transport direction which can be directly correlated with the development of transport-parallel magnetic lineation. In brittle fault zones, the degree of shear deformation can be directly correlated with the type of magnetic lineation. The fault cores, where strain and slip are localized, show a predominance of transport-parallel magnetic lineations, most probably related with the development of lineated petrofabrics. Furthermore, the minor development of shear-related petrofabrics enhance the frequency of intersection-parallel magnetic lineations, also contributing the presence of inherited, host rock petrofabrics in the fault rocks.&lt;/p&gt;

Simulation of brine migration along geological fault zones using a consistent mesh approach

2020 ◽  
Author(s):  
Falko Vehling ◽  
Firdovsi Gasanzade ◽  
Jens-Olaf Delfs ◽  
Sebastian Bauer
Keyword(s):  
Fluid Flow ◽  
Corner Point ◽  
Fault Plane ◽  
Damage Zone ◽  
Gas Injection ◽  
Gas Storage ◽  
Fault Zones ◽  
Formation Pressure ◽  
Brine Migration ◽  
Fault Damage Zone

&lt;p&gt;Upward brine migration through permeable fault damage zones could endanger near-surface drinking water resources. Deep porous rock formations offer a large potential for gas storage, like e.g. methane or CO&lt;sub&gt;2&lt;/sub&gt;. But gas injection induces formation pressure build up, that can potentially lead to vertical or horizontal brine displacement. Here fault zones play an important role as they can act either as lateral no-flow boundaries or as permeable pathways, that allow for fluid flow and pressure dissipation. Numerical reservoir simulations, which have become an important tool for investigating these effects quantitatively, have to be performed on a regional scale, in order to include the large-scale geological faults zones. Fault zones have to be implemented into the model in a geometrically and hydraulically flexible way, to account for the variety of natural conditions encountered, as e.g. open or closed fault zone.&lt;/p&gt;&lt;p&gt;In order to model that complexity, the corner point grid approach has been applied by geologists for decades. The corner point grid utilizes a set of hexahedral blocks to represent geological formations. At the fault plane, where geological layers are vertically shifted, hanging nodes appear and the corner point grid cannot be used directly, if permeable fault zones have to be represented in the model. In this study we present an extension of a mesh converter, which removes hanging nodes at the fault plane by point combination, thus providing a consistent finite element mesh. Our numerical model can account for heterogeneous hydraulic properties of the fault damage zone and the enclosed fault core. The fault core is represented by one layer of 3D finite elements on each side of the fault plane. The fault damage zone consists of a continuous layer of quadrangular 2D finite elements, which are attached at the outer face of the 3D fault core elements. This model allows for fluid flow along the fault plane while fluid flow through the fault core could be adjusted by element permeability. This concept was implemented into a workflow using the FEM-simulator OpenGeoSys in combination with a mesh converter.&lt;/p&gt;&lt;p&gt;The concept and workflow are shown to run stable using dedicated test cases for method validation, accounting for the coupled transport of water, heat and salt mass for different fault zone setups in a synthetic multi-layered subsurface. Here we focused on brine displacement and uprising due to formation pressure increase after gas injection, which is numerically realized by Dirichlet pressure boundary conditions. Further, we will investigate the relation between computational efficiency and flow solution differences by comparing this concept with the approach of fully discretized faults. Additionally, we will apply our workflow on a real geological case in the Northern German Basin, where a fault system is close to a potential gas storage side. &amp;#160;&lt;/p&gt;

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