Geometrical comparison of outcrop data and discrete element models of extensional fault zones in layered carbonates

2020 ◽  
Author(s):  
Hagen Deckert ◽  
Steffen Abe ◽  
Wolfgang Bauer
Keyword(s):  
Fluid Flow ◽  
Fault Zone ◽  
Seismic Data ◽  
Discrete Element ◽  
Fault Zones ◽  
Normal Faults ◽  
Small Displacement ◽  
Small Scale ◽  
Burial Depth ◽  
Multiple Fault

<p>In the course of hydrocarbon or geothermal exploration the characterisation of fault zone architectures is of interest for fluid flow modelling and geomechanical studies. Seismic data normally offer the best information for the identification of fault zone geometries in sedimentary basins. However, the internal structure or the damage zone of a fault can be hardly resolved with seismic data as displacements along single fault strands or fractures are by far too small. Thus, it is not possible to directly map small scale faults with seismic methods, though these structures might significantly influence fluid flow. We try to examine the architecture of extensional fault zones in carbonate rocks at subseismic scales by using discrete element method (DEM) techniques to numerically simulate the evolution of fault zones including their associated damage zones.</p><p>As a case study we have analysed the geometry, displacement and fault width of normal faults in fine grained jurassic limestones in a quarry in Franconia, Germany. The quarry shows a rather simple set of conjugated 60deg dipping normal faults. Displacement is rather small and varies between c. 5cm up to c. 2m, some faults show almost no offset. The fault thickness varies between 2cm and c. 1m. A closer investigation of the fault geometries reveals, next to planar parts, sometimes complex fault zone structures including restraining and releasing bends, multiple fault strands as well as lenses and associated riedel shears. Analysis of high resolution photogrammetric data revealed a high number of small scale fractures between neighbouring discrete fault surfaces which are interpreted as highly fractured damage zones. Some faults with rather small displacement suggest that the overall inclination of the fault is a result of small subvertical sections which are connected in a staircase like appearance. </p><p>The DEM models simulate normal faulting in a layered marl-limestone sequence driven by the displacement of an underlying basement fault. Different layer geometries and effective vertical stresses in the range of 15-45 MPa, equivalent to an overburden thickness of c. 1000-3000m, have been used in the models. The stress range covers the maximum burial depth of the carbonates, which is assumed to be c. 1500m. Material properties used in the DEM were calibrated based on laboratory data, i.e. results of triaxial deformation tests on the studied limestones.</p><p>Results of the models show fault geometries which resemble those observed in the studied outcrop. In particularly under low stress, small offsets and with strongly decoupled layers we observe steeply dipping faults (>70deg) which also show staircase structures composed of sub-vertical fractures within each of the layers and horizontal offsets along the layer interfaces. We also observe the development of multiple fault strands and associated damage zones. </p><p>Our study shows that the DEM models are capable to reproduce observed fault geometries and damage zones. The results help to understand fault zone architectures and depict highly fractured areas in a sub-seismic scale.</p>

3D geometry of outcrop-scale normal faults from Taranaki, New Zealand

2020 ◽  
Author(s):  
Inbar Vaknin ◽  
Andy Nicol ◽  
Conrad Childs
Keyword(s):  
New Zealand ◽  
Fault Zone ◽  
Slip Surface ◽  
Geometric Model ◽  
Fault Zones ◽  
Normal Faults ◽  
Small Scale ◽  
Fault Geometry ◽  
Fault Rock ◽  
Fault Surface

<p>Fault surfaces and fault zones have been shown to have complex geometries comprising a range of morphologies including, segmentation, tip-line splays and slip-surface corrugations (e.g., Childs et al., 2009*). The three-dimensional (3D) geometries of faults (and fault zones) is difficult to determine from outcrop data which are typically 2D and limited in size. In this poster we examine the small-scale geometries of faults from normal faults cropping out in well bedded parts of the Mount Messenger and Mahakatino formations in Taranaki, New Zealand. We present two main datasets; i) measurements and maps of 2D vertical and horizontal sections for in excess of 200 faults and, ii) 3D fault model of a small-fault (vertical displacement ~1 cm) produced by serial fault-perpendicular sections of a block 10x10x13 cm. The sectioned block contains a single fault that offsets sand and silt layers, and comprises two main dilational bends; in the 3D model we map displacement, bedding and fault geometry for the sectioned fault zone. Faults in the 2D dataset comprise a range of geometries including, vertical segmentation, bends, splays and fault-surface corrugations. Although we have little information on the local magnitudes and orientations of stresses during faulting, geometric analysis of the fault zones provides information on the relationships between bed characteristics (e.g., thickness, induration and composition) and fault-surface orientations. The available data supports the view that the strike and dip of fault surfaces vary by up to 25° producing undulations or corrugations on fault surfaces over a range of scales from millimetres to metres and in both horizontal and vertical directions. Preliminary analysis of the available data suggests that these corrugations appear to reflect fault refractions due to changing bed lithologies (unexpectedly the steepest sections of faults are in mudstone beds), breaching of relays and development of conjugate fault sets. The relative importance of these factors and their importance for fault geometry will be explored further in the poster.</p><p> </p><p>*Childs, C., Walsh, J.J., Manzocchi, T., Bonson, C., Nicol A., Schöpfer, M.P.J. 2009. A geometric model of fault zone and fault rock thickness variations. Journal of Structural Geology 31, 117-127.</p>

Iron Oxide (U–Th)/He Thermochronology: New Perspectives on Faults, Fluids, and Heat

Elements ◽  
2020 ◽  
Vol 16 (5) ◽  
pp. 319-324
Author(s):  
Emily H. G. Cooperdock ◽  
Alexis K. Ault
Keyword(s):  
Fluid Flow ◽  
Iron Oxide ◽  
Heat Exchange ◽  
Iron Oxides ◽  
Fault Zone ◽  
Frictional Heating ◽  
Fault Zones ◽  
Chemical Behavior ◽  
Rock Interaction ◽  
Dynamic Motion

Fault zones record the dynamic motion of Earth’s crust and are sites of heat exchange, fluid–rock interaction, and mineralization. Episodic or long-lived fluid flow, frictional heating, and/or deformation can induce open-system chemical behavior and make dating fault zone processes challenging. Iron oxides are common in a variety of geologic settings, including faults and fractures, and can grow at surface-to magmatic temperatures. Recently, iron oxide (U–Th)/He thermochronology, coupled with microtextural and trace element analyses, has enabled new avenues of research into the timing and nature of fluid–rock interactions and deformation. These constraints are important for understanding fault zone evolution in space and time.

scholarly journals Elastic and Frictional Properties of Fault Zones in Reservoir-Scale Hydro-Mechanical Models—A Sensitivity Study

Energies ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4606
Author(s):  
Torben Treffeisen ◽  
Andreas Henk
Keyword(s):  
Fault Zone ◽  
Sensitivity Study ◽  
Fault Zones ◽  
Small Scale ◽  
Fe Model ◽  
Angle Of Internal Friction ◽  
Fault Properties ◽  
Mechanical Models ◽  
The Difference ◽  
A Minor

The proper representation of faults in coupled hydro-mechanical reservoir models is challenged, among others, by the difference between the small-scale heterogeneity of fault zones observed in nature and the large size of the calculation cells in numerical simulations. In the present study we use a generic finite element (FE) model with a volumetric fault zone description to examine what effect the corresponding upscaled material parameters have on pore pressures, stresses, and deformation within and surrounding the fault zone. Such a sensitivity study is important as the usually poor data base regarding specific hydro-mechanical fault properties as well as the upscaling process introduces uncertainties, whose impact on the modelling results is otherwise difficult to assess. Altogether, 87 scenarios with different elastic and plastic parameter combinations were studied. Numerical modelling results indicate that Young’s modulus and cohesion assigned to the fault zone have the strongest influence on the stress and strain perturbations, both in absolute numbers as well as regarding the spatial extent. Angle of internal friction has only a minor and Poisson’s ratio of the fault zone a negligible impact. Finally, some general recommendations concerning the choice of mechanical fault zone properties for reservoir-scale hydro-mechanical models are given.

Seismic imaging and statistical analysis of fault facies models

2017 ◽  
Vol 5 (4) ◽  
pp. SP71-SP82 ◽  
Author(s):  
Dmitriy R. Kolyukhin ◽  
Vadim V. Lisitsa ◽  
Maxim I. Protasov ◽  
Dongfang Qu ◽  
Galina V. Reshetova ◽  
...  
Keyword(s):  
Fault Zone ◽  
Seismic Data ◽  
Structural Complexity ◽  
Fault Zones ◽  
Rock Properties ◽  
Zone Structure ◽  
Structure And Property ◽  
Subsurface Fluid ◽  
The Impact ◽  
Seismic Images

Interpretation of seismic responses from subsurface fault zones is hampered by the fact that the geologic structure and property distributions of fault zones can generally not be directly observed. This shortcoming curtails the use of seismic data for characterizing internal structure and properties of fault zones, and it has instead promoted the use of interpretation techniques that tend to simplify actual structural complexity by rendering faults as lines and planes rather than volumes of deformed rock. Facilitating the correlation of rock properties and seismic images of fault zones would enable active use of these images for interpreting fault zones, which in turn would improve our ability to assess the impact of fault zones on subsurface fluid flow. We use a combination of 3D fault zone models, based on empirical data and 2D forward seismic modeling to investigate the link between fault zone properties and seismic response. A comparison of spatial statistics from the geologic models and the seismic images was carried out to study how well seismic images render the modeled geologic features. Our results indicate the feasibility of extracting information about fault zone structure from seismic data by the methods used.

Faults and magma reservoirs along the Southern Andes Volcanic zone (SAVZ): linking oservations and numerical models of stress change controlling magmatic and hydrothermal fluid flow

2020 ◽  
Author(s):  
Javiera Ruz ◽  
Muriel Gerbault ◽  
José Cembrano ◽  
Pablo Iturrieta ◽  
Camila Novoa Lizama ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Stress Field ◽  
Fault Zone ◽  
Numerical Models ◽  
Fluid Pressure ◽  
Seismic Inversion ◽  
Fault Zones ◽  
Fault System ◽  
Far Field ◽  
Trigger Failure

<p> The Chilean margin is amongst the most active seismic and volcanic areas on Earth. It hosts active and fossil geothermal and mineralized systems of economic interest documenting significant geofluid migration through the crust. By comparing numerical models with field and geophysical data, we aim at pinning when and where fluid migration occurs through porous domains, fault zone conduits, or remains stored at depth awaiting a more appropriate stress field. <span>Dyking and volcanic activity occur within fault zones</span> <span>along the S</span><span>A</span><span>VZ, linked with stress field variations</span> <span>in spatial and temporal association with</span> –<span>short therm-</span> <span>seismicity</span> <span>and -long term- oblique </span><span>plate </span><span>convergence.</span> <span>Volcanoes and geothermal domains are mostly located along or at the intersection of margin-oblique fault zones (Andean Transverse Faults), and along margin-parallel strike slip zones, some which may cut the entire lithosphere (Liquiñe-Ofqui fault system). Wh</span><span>ereas</span><span> the big picture displays</span> <span>fluid flow straight to the surface, at close look significant offsets between crustal structures occur. 3D numerical models using conventional elasto-plastic rheology provide insights on the interaction of (i) an inflating magmatic cavity, (ii) a slipping fault zone, and (iii) regional tectonic stresses. Applying either (i) a magmatic overpressure or (ii) a given fault slip can trigger failure of the intervening rock, and generate either i) fault motion or ii) magmatic reservoir failure, respectively, but only for distances less than the structures' breadth even at low rock</span> <span>strength. However, at greater inter-distances the bedrock domain in between the fault zone and the magmatic cavity undergoes dilatational strain of the order of 1-5x10-5. This dilation opens the bedrock’s pore space and forms «pocket domains» that may store up-flowing over-pressurized fluids, which may then further chemically</span> interact<span> with the bedrock, for the length of time</span> <span>that</span> <span>these pockets remain open. These porous pockets</span> <span>can reach kilometric size, questioning their parental link with outcropping plutons along the margin. Moreover, bedrock permeability may also increase as fluid flow diminishes effective bedrock friction and cohesion. Comparison with rock experiments indicates that such stress and fluid pressure changes may eventually trigger failure at the intermediate timescale (repeated slip or repeated inflation). Finally, incorporating far field compression (iii)</span> <span>loads the bedrock to</span> <span>a state of stress at the verge of failure. Then, failure around the magmatic </span><span>reservoir</span><span> or </span><span>at</span> <span>the fault zone occurs for lower load</span><span>ing</span><span>.</span> <span>Permanent tectonic loading on the one hand, far field episodic seismic inversion of the stress field on the other, and localized failure all together promote a transient stress field, thus explaining the occurrence of transient fluid pathways on seemingly independent timescales. These synthetic models are then discussed with regards to specific cases along the SVZ, particularly the Tatara-San Pedro area (~36°S), where magnetotelluric profiles </span><span>document</span><span> conductive volumes at different depths underneath active faults, volcanic edifices and geothermal vents. We discuss the mechanical link between these deep sources and surface structures</span>.</p>

Dating faults, fractures and fluids with U-Pb calcite geochronology: Application to contrasting fracture and fluid-flow modes of the Cleveland Basin

2020 ◽  
Author(s):  
Jack Lee ◽  
Nick Roberts ◽  
Robert Holdworth ◽  
Andrew Aplin ◽  
Richard Haslam ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Fault Zone ◽  
Failure Modes ◽  
Damage Zone ◽  
Source Rocks ◽  
Normal Faults ◽  
Fluid Composition ◽  
Natural Fractures ◽  
Seal Integrity ◽  
Clumped Isotope

<p>Fractures and faults act as important permeable pathways in the subsurface and are of great significance to the petroleum industry and for future Carbon Capture and Storage. Fractures allow fluid-flow through impermeable units such as mudrocks and can affect how these lithologies act as top seals, source rocks and/or unconventional reservoirs. Natural fractures within mudrocks can strongly influence top seal integrity, primary migration and the performance of unconventional (e.g. shale gas) reservoirs. This project studies the exhumed, early-mature, Jurassic mudrock succession of the Cleveland Basin, NE England, combining structural geology with isotope geochemistry and geochronology. The primary objective is to provide an absolute chronology of faulting and fracturing through novel U-Pb geochronology of fracture-fill calcite. The abundance of well-exposed, natural fractures with different orientations and failure modes provides an opportunity to investigate the properties of these fractures, and provide a basin-wide temporal and spatial framework of evolving deformation. The second objective is to use trace element, stable isotope, and clumped isotope analyses, to constrain fluid composition and temperature. In combination, these objectives will provide an integrated understanding of fracturing, faulting and fluid migration during burial and exhumation of a sedimentary basin.</p><p>Current fracture-fill dates from U-Pb geochronology provide intriguing insights into the history of the Cleveland Basin. We have identified and dated three phases of deformation and associated fluid-flow that have contrasting kinematics and fluid-flow regimes. The E-W trending Flamborough Head Fault Zone (FHFZ) bounds the basin to the south, and calcite preserved in one of the major extensional faults provides ages of 64-56 Ma. Calcite from N-S to NNW-SSE trending normal faults and associated fractures in the north of the Cleveland Basin provide ages of 44-25 Ma, revealing a previously unknown phase of Cenozoic faulting, which we speculatively relate to salt-related deformation. Structural and petrographic information suggest that the E-W and N-S trending faults have contrasting fracture-fluid-flow systems. Large (up to 30 cm), chalk hosted, vuggy calcite cements with geopetal sediment-fills in the E-W fault zone suggest it acted as an open fluid conduit with voluminous fluid-flow, linking the shallow sub-surface with deeper levels of the stratigraphy. In contrast, typically thin (<5 mm) vein fills with varying crack-seal-slip type textures in the N-S mudstone-hosted fractures of the Cleveland Basin provide evidence of episodic slip of variable displacement (44-40 Ma); these fracture openings may partly be controlled by pore fluid pressures and pre-date fault movement along the regional Peak Fault and smaller scales N-S faults (40-25 Ma) which are characterised by damage zone calcite mineralisation and extensional jog structures. Initial stable isotopic results are giving indications of fluid temperatures and sourcing which will be built on further by clumped isotope and fluid inclusions work.</p>

Numerical simulation of the in situ stress in a high-rank coal reservoir and its effect on coal-bed methane well productivity

2018 ◽  
Vol 6 (2) ◽  
pp. T271-T281 ◽  
Author(s):  
Shuai Yin ◽  
Airong Li ◽  
Qiang Jia ◽  
Wenlong Ding ◽  
Yanxia Li
Keyword(s):  
Stress Field ◽  
In Situ Stress ◽  
Coal Bed ◽  
Coal Bed Methane ◽  
Small Displacement ◽  
Small Scale ◽  
Burial Depth ◽  
Single Well ◽  
Coal Reservoir

In situ stress has an important influence on coal reservoir permeability, fracturing, and production capacity. In this paper, fracturing testing, imaging logging, and 3D finite-element simulation were used to study the current in situ stress field of a coal reservoir with a high coal rank. The results indicated that the horizontal stress field within the coal reservoir is controlled by the burial depth, folding, and faulting. The [Formula: see text] and [Formula: see text] values within the coal reservoir are 1–2.5 MPa higher than those within the clastic rocks of the roof and floor. The [Formula: see text]–[Formula: see text] values of the coal reservoir are generally between 2 and 6 MPa and increase with burial depth. When the [Formula: see text]–[Formula: see text] value is less than 5 MPa, production from a single well is high, but when the [Formula: see text]–[Formula: see text] value is greater than 5 MPa, production from a single well is low. In addition, the accumulated water production is high when the [Formula: see text]–[Formula: see text] value is greater than 5 MPa, demonstrating that a higher [Formula: see text]–[Formula: see text] value allows the hydraulic fractures to more easily penetrate the roof and floor of the coal seam. In coal-bed methane development regions with high [Formula: see text]–[Formula: see text] values, repeated fracturing using the small-scale plug removal method — which is a fracturing method that uses a small volume of liquid, small displacement, and low sand concentration — is suggested.

scholarly journals On morphology and amplitude of 2D and 3D thermal anomalies induced by buoyancy-driven flow within and around fault zones

2020 ◽  
Author(s):  
Laurent Guillou-Frottier ◽  
Hugo Duwiquet ◽  
Gaëtan Launay ◽  
Audrey Taillefer ◽  
Vincent Roche ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Fault Zone ◽  
3D Models ◽  
Fault Zones ◽  
Rock Properties ◽  
Thermal Anomalies ◽  
Flow Models ◽  
Temperature Anomalies ◽  
Vertical Fault ◽  
Dip Angle

Abstract. In the first kilometres of the subsurface, temperature anomalies due to heat conduction processes rarely exceed 20–30 °C. When fault zones are sufficiently permeable, fluid flow may lead to thermal anomalies much higher, as evidenced by the emergence of thermal springs or by fault-related geothermal reservoirs. Hydrothermal convection triggered by buoyancy effects creates thermal anomalies whose morphology and amplitude are not well known, especially when depth- and time-dependent permeability are considered. Exploitation of shallow thermal anomalies for heat and power production partly depends on the volume and on the temperature of the hydrothermal reservoir. This study presents a non-exhaustive numerical investigation of fluid flow models within and around simplified fault zones, where realistic fluid and rock properties are accounted for, as well as appropriate boundary conditions. 2D simplified models point out relevant physical mechanisms for geological problems, such as thermal inheritance or splitting plumes showing a pulsating behaviour. When permeability is increased, the classic finger-like upwellings evolve towards a bulb-like geometry, resulting in a large volume of hot fluid at shallow depth. In the simplified 3D models, where fault zone dip angle and fault zone thickness are varied, the anomalously hot reservoir exhibits a kilometre-sized hot air balloon morphology, or, when permeability is depth-dependent, a funnel-shape geometry. For thick faults, the number of thermal anomalies increases but not the amplitude. The largest amplitude (up to 80–90 °C) is obtained for vertical fault zones. At the top of a vertical, 100 m wide, fault zone, temperature anomalies greater than 30 °C may extend laterally over more than 1 km from the fault boundary. These preliminary results should motivate further geothermal investigations of more elaborated models where topography and fault intersections would be accounted for.

scholarly journals Active Faulting in Lake Constance (Austria, Germany, Switzerland) Unraveled by Multi-Vintage Reflection Seismic Data

2021 ◽  
Vol 9 ◽  
Author(s):  
S.C. Fabbri ◽  
C. Affentranger ◽  
S. Krastel ◽  
K. Lindhorst ◽  
M. Wessels ◽  
...  
Keyword(s):  
Fault Zone ◽  
Seismic Data ◽  
Single Channel ◽  
Fault Zones ◽  
Lake Constance ◽  
Earthquake Catalog ◽  
Tectonic Structures ◽  
Reflection Seismic ◽  
The North ◽  
Major Fault

Probabilistic seismic hazard assessments are primarily based on instrumentally recorded and historically documented earthquakes. For the northern part of the European Alpine Arc, slow crustal deformation results in low earthquake recurrence rates and brings up the necessity to extend our perspective beyond the existing earthquake catalog. The overdeepened basin of Lake Constance (Austria, Germany, and Switzerland), located within the North-Alpine Molasse Basin, is investigated as an ideal (neo-) tectonic archive. The lake is surrounded by major tectonic structures and constrained via the North Alpine Front in the South, the Jura fold-and-thrust belt in the West, and the Hegau-Lake Constance Graben System in the North. Several fault zones reach Lake Constance such as the St. Gallen Fault Zone, a reactivated basement-rooted normal fault, active during several phases from the Permo-Carboniferous to the Mesozoic. To extend the catalog of potentially active fault zones, we compiled an extensive 445 km of multi-channel reflection seismic data in 2017, complementing a moderate-size GI-airgun survey from 2016. The two datasets reveal the complete overdeepened Quaternary trough and its sedimentary infill and the upper part of the Miocene Molasse bedrock. They additionally complement existing seismic vintages that investigated the mass-transport deposit chronology and Mesozoic fault structures. The compilation of 2D seismic data allowed investigating the seismic stratigraphy of the Quaternary infill and its underlying bedrock of Lake Constance, shaped by multiple glaciations. The 2D seismic sections revealed 154 fault indications in the Obersee Basin and 39 fault indications in the Untersee Basin. Their interpretative linkage results in 23 and five major fault planes, respectively. One of the major fault planes, traceable to Cenozoic bedrock, is associated with a prominent offset of the lake bottom on the multibeam bathymetric map. Across this area, high-resolution single channel data was acquired and a transect of five short cores was retrieved displaying significant sediment thickness changes across the seismically mapped fault trace with a surface-rupture related turbidite, all indicating repeated activity of a likely seismogenic strike-slip fault with a normal faulting component. We interpret this fault as northward continuation of the St. Gallen Fault Zone, previously described onshore on 3D seismic data.

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