Fault Zones Abstract Book

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Fault Zones: Structure, Geomechanics and Fluid Flow

September 2008 Page 1

Fault Zones: Structure,Geomechanics and

Fluid Flow

16-18 September 2008

The Petroleum Group would like to thank BadleyGeoscience, BP and Shell for their support of

this event:


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Tuesday 16 September

08:30 Registration + coffee

09:00 Welcome and opening

09:10 Caine (US Geological Survey)KEYNOTE: New Insight on Structural Inheritance and Fault-Vein Permeability Structures in theColorado Mineral Belt, USA

Session 1Structural Properties of Fault Zones

09:40 Gudmundsson (University of London)

Local stresses, fracture apertures, and fluid transport in fault zones

10:00 Reeves (BGS)Repository Excavations and the Self Sealing of the Excavation Damaged Zone (EDZ) inMudrocks: An Overview

10:20 Shackleton (Midland Valley)Can strain maps be used as an indicator for the extent of fault zone damage?

10:40 Yonkee (Weber State Universi ty)Geometry, Kinematics, and Fracture Network Characteristics with Fault Segment Boundaries,

Wasatch Fault Zone, Utah, USA

11:00 Tea / Coffee

11:30 Schueller (University of Bergen)Characterization of fault damage zone and deformation band populations based on outcropdata

11:50 Wibberley (Total)Mechanics of fault-zone localisation in high-porosity sandstones and impact on flow efficiency

12:10 McLellan (James Cook University)Strain accumulation and fluid flow in and around basin bounding fault zones of the LeichhardtRiver Fault Trough, Qld. Australia

12:30 Agosta (Universita Di Camerino)Structural and statistical analyses of fault-controlled hydrocarbon migration andaccumulation

12:50 Lunch


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14:00 Schlische (Rutgers University)Experimental modeling of extensional fault domains and fault-domain boundaries (transferzones / accommodation zones)

14:20 Thornton (Rockfield Software Limited)Predictive Modelling of the Evolution of Fault Zone Structure: 3-D Sandbox and Field ScaleModelling

14:40 Henza (Rutgers Universit y)Influence of pre-existing fabric on normal-fault development: An experimental study

15:00 Granger (Haley & Aldr ich, Inc)Fault-surface corrugations: Insights from scaled experimental models of extension

15:20 Nottveit (University of Bergen)Fault Facies modeling; possibilities and difficulties

15:40 Freeman (Badley Geoscience Ltd)Using empirical geological rules to reduce structural uncertainty in seismicinterpretation of faults

16:00 Tea / Coffee

16:30 Tueckmantel (University of Leeds)Fault seal prediction of seismic-scale normal faults in porous sandstone: A case study from theeastern Gulf of Suez rift, Egypt

16:50 Frost (University of Southern California)Structural analysis of the exhumed SEMP fault zone, Austria: Towards an understanding offault zone architecture and mechanics throughout the seismogenic crust

17:10 Braathen (University of Bergen)Fault Facies methodology for systematizing analogue outcrop data to 3D fault grids inreservoir models

17:30 Agar (ExxonMobi l)What are the Potential Impacts of Low-offset Faults on Carbonate Reservoir Performance?

17:50 Childs (University College Dublin)KEYNOTE: A geometric model for the development of fault zone and fault rock thicknessvariations

18:35 Wine Reception


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Wednesday 17 September


09:00 Rice (Harvard University)KEYNOTE: How granulated/cracked fault border zones, and their pore fluids, interact withearthquake rupture dynamics

Session 2Fault/fracture mechanisms and mechanics

09:30 Haimson (University of Wiscons in)The effect of the intermediate principal stress on shear band strike and dip in the siltstonestraddling the active Chelungpu Fault, Taiwan

09:50 Greenhough (University of Edinburgh)Geomechanical sensitivity of reservoirs from statistical correlations of flow rates

10:10 Van Marcke (EIG Eurid ice)Excavation induced fractures in a plastic clay formation: observations at the HADES URF

10:30 Tea / Coffee

11:00 Aydin (Stanford University)Fault growth and the related fundamental physical processes

11:20 Moir (University of Strathclyde)Modelling development of a simple fault zone in the Sierra Nevada

11:40 Mitchell (University of Hawaii)Mechanics of sheeting joints

12:00 Ishii (Japan Atomic Energy Agency)Relationship between growth mechanism of faults and permeability variations with depth ofsiliceous mudstone in northern Hokkaido, Japan

12:20 Welch (University of Leeds)

Fault growth in mechanically layered sequences: A modelling approach

12:40 Lunch

13:30 Jostad (Norwegian Geotechnical Institute)Geomechanical integrity of a sealing fault during late life depletion of a petroleum reservoir

13:50 Zhang (GRS)Experimental study on self-sealing of indurated clay


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14:10 Muhuri (Chevron)Kinetics of Time-dependent Processes in Fault Zones: Implications for Fault Seal Analysis

14 :30 Niemeijer (Pennsylvania State University)

Strong velocity weakening in fault gouges: results from rock analogue experiments

14 :50 Zhang (Chinese Academy of Sciences)Characterisation of fault sealing for hydrocarbon migration and entrapment

15:10 Tea / Coffee

Session 3Fault Structure and Earthquakes

15 :40 Bennington (University of Wisconsin )Constrained Inversions of Geophysical Data in the Parkfield Region of California

16 :00 Cooke (University of Massachusetts)The role of slip-weakening friction in damage zone geometry

16 :20 De Paola (University of Durham)The Nucleation of Large Earthquakes Within Overpressured Fault Zones in EvaporiticSequences

16 :40 Evans (Utah State University)The nature of the San Andreas Fault at seismogenic depths: Insight from direct access via theSAFOD boreholes

17 :00 Wojtal (Oberlin College)Displacement field in the borderlands of the San Andreas Fault, Durmid Hill, CA and the originof late sinistral faults

17 :20 Nicol (GNS Science, New Zealand)Fault Interactions and the Growth of Faults on Earthquake and Geological Timescales

17 :40 Cowie (University of Edinburgh)KEYNOTE: Quantifying Fault Slip rates and Earthquake Clustering along Active Normal Faultsin Central Italy: Insights from Cosmogenic Exposure Dating and Numerical Modelling

19 :00 Conference Dinner


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Thursday 18 September


09:00 Talwani (University of South Carolina)KEYNOTE: Seismogenic Permeability

Session 3 contdFault Structure and Earthquakes

09:30 Pitarello (Universita degli Studi di Padova)Energy partitioning during seismic slip in pseudotachylyte-bearing faults (Gole Larghe Fault,Adamello, Italy)

09:50 Balsamo (Universita Roma Tre)Particle size distribution analysis in pristine and faulted quartz-rich, poorly cohesivesandstones: influence of analytical procedures in laser diffraction analysers

10:10 Spivak (Institute o f Geospheres Dynamics of Russian Academy of Sciences)Rigidity of tectonic faults and their temporal variation

10:30 El Hariri (University of Boston)The role of fluids in triggering earthquakes: Observations from reservoir induced earthquakes

10:50 Tea / Coffee

Session 4Faults and fluids

11:15 Medeiros (UFRN, Natal)Results from field pumping experiments testing connectivity across deformation bands inTucano Basin, NE Brazil

11:35 Guillemot (Andra)Different scales of fracturing in the Callovo-Oxfordian argillite of the Meuse /Haute-Marne AndraURL area, France

11:55 Liberty (Boise State University)

Fault imaging in the western US using high resolution seismic reflection methods

12:15 Brinton (University of Idaho)The influence of regional stress on geostatistical patterns of fault permeability at SmithCreek Hot Springs, Neveda, USA

12:35 Masset (Swiss Federal Institute of Technology)Large scale Hydraulic Properties of Faults and Fault Zones of the Central Aar and GotthardMassifs (Switzerland)


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12:55 Lunch

Session 4 contdFaults and fluids

13:45 Woods (BP Institute)Buoyancy driven gas dispersion along an inclined low permeability boundary

14:05 Amano (Japan Atomic Energy Agency)3D Structures of Permeable and Impermeable Faults in Granite: A Case Study in the MizunamiUnderground Research Laboratory, Japan

14:25 Tveranger (University of Bergen)Volumetric fault zone modelling using fault facies

14 :45 Wilson (Stanford University)Using outcrop observations, 3D discrete feature network (DFN) fluid flow simulations, and

subsurface data to constrain the impact of normal faults and opening mode fractures on themigration and concentration of hydrocarbons in an active asphalt mine

15:05 Rocher (IRSN, France)Differential fracturing pattern in clay/limestone alternations at Tournemire (Aveyron, France)and in the Maltese Islands

15 :25 Caine (US Geolog ical Survey)Contrasting Styles of Faults and Fault Rocks in the Rio Grande Rift of Central New Mexico,USA: Their Relationships to Rift Architecture and Groundwater Resources

15:45 Tea / Coffee

16:10 Lunn (University of Strathclyde)Assessing temporal changes in fault permeability for radioactive waste disposal

16:30 Simms (John Hopkins University)Fault zone control of fluid flow in extensional basins

16:50 Peacock (Fugro Robertson Ltd)Pull-aparts, scaling and fluid flow

17:10 Cuisiat (Norwegian Geotechnical Institute)Fault formation in uncemented sediments. Insight from laboratory experiments

17:30 Younger (University of Newcastle)KEYNOTE: Extraordinary permeability associated with major W-E rock-mass discontinuitiescutting Carboniferous strata in northern England and central Scotland - some cautionary tales

18 :00 Conference End


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Posters


BastesenExtensional fault cores in carbonates; thickness-displacement relationships

Novakova (tbc)Reactivation of brittle tectonic structures in the Sudetic Marginal Fault vicinity (in north east of BohemianMassif)

Cunningham (SRK Consul ting)

The role of faulting in the concentration of Fe and Zn-Pb ores within the Paleoproterozoic Earaheedy Basin,Western Australia

Bell (National Oceanography Centre)Fault development and control on rift basin evolution in the Gulf of Corinth, Greece

Mller (University of Vienna)Fault zone characteristics of a low-angle normal fault on northern Kea (Western Cyclades, Greece)

Alessandroni (Universi ta d i Camerino)Statistical analysis of stylolites and sheared stylolites in layered carbonate rocks: an attempt for a newmethodological approach

Kanjanapayont (University of Vienna)Kinematics of the Klong Marui continental wrench fault, southern Thailand

Taylor (University of Manchester)A three-dimensional approach to the interpretation of major fault zone properties


Ikari (tbc)

Pore pressure generation in sheared marine sediments

Smith (Durham)Laboratory measurements of the frictional strength of a natural low-angle normal fault: the Zuccale fault,Elba Island, Italy

Storti (Universita Roma Tre)Influence of analytical methods on fault core rock particle size distributions obtained from laser-aidedanalysers


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Mittempergher (Museo Tridentino di Scienze Naturali)Effects of fault orientation on fault rock assemblages of exhumed seismogenic sources

Haimson (University of Wisconsin)

The effect of the intermediate principal stress on shear band strike and dip in the siltstone straddling theactive Chelungpu Fault, Taiwan

Sehhati (Washington State University)Porosity and particle shape changes leading to shear localization in small-displacement faults

Thursday 18 September

Lawther (University of Glasgow)Fluid-fault-rock interactions in faults exhumed from seismogenic depths

Kirkpatrick (University of Glasgow)Fault structure, slip and fluid flow interactions; insights from small seismogenic faults

Fachri (University of Bergen)Sensitivity of fluid flow to faulted siliciclastic reservoir configurations

Pittarrello (Universita degli Studi di Padova)Deep-seated pseudotachylytes from the Ivrea Zone metagabbros (Southern Alps, Italy)

Mittempergher (Museo Tridentino di Scienze Naturali)Hydrogen isotopes in natural and experimental pseudotachylyte-bearing faults: the origin of fluids atseismogenic depth


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KEYNOTE:

New Insight on Structural Inheritance and Fault-Vein Permeability Structures in theColorado Mineral Belt, USA

Jonathan Saul CaineU.S. Geological Survey, P.O. Box 25046, MS 964, Denver, CO, 80225, [email protected]

A long history of mining and geologic mapping in the Front Range of the central ColoradoRocky Mountains has resulted in an exceptionally rich dataset on the geologic structure ofepithermal ore deposits. These regional-scale data were among the first to lead geologists toponder the role of Precambrian structural inheritance in the localization of Tertiary mineraldeposits. Of particular significance was the idea that localization of epithermal, polymetallicfault-veins in this region was controlled by a pre-existing crustal weakness, the ProterozoicIdaho Springs-Ralston ductile shear zone (ISRZ). However, recent compilation of structuraland mineral deposit data from existing 1:24,000 geologic maps, reports, argon geochronologyon fault and hydrothermally altered rocks, and new structural data from outcrop in the Front

Range results in five major observations: 1) There is little correlation between the locations ofinferred mineral deposit-related plutons and the ISRZ or major brittle fault zones. 2) Mappedfeatures suggest that myriad directions of potential permeability structures existed during theTertiary and that metalliferous hydrothermal fluids may have flowed in many directions at anygiven time during evolution of the Colorado Mineral Belt. 3) Small displacement fault-veins withstriated and cataclasized margins that carried ore bearing fluids show steep dips and eitherpreferential ENE trends well correlated with model paleostress directions for the Laramideorogeny or radial trends around Late Cretaceous to Tertiary igneous intrusions. Theserelationships hold regardless of co-planarity with preexisting foliations in metasediments or inmassive unfoliated metaigneous plutons. 4) The total gas

40Ar/

39Ar age of alteration is older

than that of the brittle faults and none are Proterozoic. 5) There are only minor differences inorientation and intensity of potential structures that may have controlled permeability fromwithin the ISRZ compared with similar structures outside the ISRZ. These observations

suggest that Proterozoic inheritance in the Front Range is not the primary control of mineraldeposit permeability structure, location, or orientation. Rather, responsible processes likelyinclude a) proximity to shallowly emplaced plutons, b) self-generated, hydro-fracturing-likepermeability due to thermally driven pore fluid pressure changes associated with plutonemplacement; and c) competition between varying magnitudes and orientations of shallowregional horizontal principal stresses, overburden load, and local stress perturbations related topluton emplacement.


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Local stresses, fracture apertures, and fluid transport in fault zones

Agust Gudmundsson1, Shigekazu Kusumoto

2, Silje S. Berg

3, Trine S. Simmenes

3, Belinda

Larsen3, Sonja L. Philipp

4

1

Department of Earth Sciences, Royal Holloway University of London, UK2School of Marine Science and Technology, Tokai University, Shizuoka, Japan

3Department of Earth Science, University of Bergen, Norway

4Geoscience Centre, University of Gottingen, Germany

Many fault zones are mechanically very heterogeneous and develop heterogeneous localstresses. At depth, much of the fluid transport in active fault zones is through fractures thatsubsequently become mineral veins. Measurements of many veins, mostly 2-6 m long (strikedimension), with a maximum thickness of 10-25 mm, show that the aperture (thickness)normally varies irregularly along the vein length; commonly by 20-40%, but occasionally by 50-70%, of the maximum vein thickness. Such aperture variations may lead to flow channellingand significantly affect fluid transport in fault zones. Most veins are extension fractures, thestress acting perpendicular to them being the minimum compressive (maximum tensile)

principal stress, S3. For such fractures, we define overpressure as the total fluid pressure in thefracture minus S3. In a fault zone where the local stress is heterogeneous, fractureoverpressure may vary irregularly. Here we use Fourier cosine series to provide analyticalsolutions for the displacement and stress fields around a fracture opened by an irregularoverpressure. The solutions can be used to estimate the aperture variation of essentially anyfluid-driven extension-fracture. The results should improve our understanding of fluid transportand flow channelling, as well as that of local stresses and displacements, in fault zones.


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Repository Excavations and the Self Sealing of the Excavation Damaged Zone (EDZ) inMudrocks: an Overview

H.J. Reeves, R.J. Cuss & J.F. Harrington

When a repository opening (tunnel, shaft, gallery or disposal vault is excavated, the stressesacting in the rock are altered by the tunneling activities and by the removal of the rock from thecross-section of newly-formed excavation. A zone of stress concentration is formed around allthe underground excavations in rock. Close to the walls of an excavation, the radial stress fallsand the tangential stress rises. The maximum shear stress is determined by the differencebetween these two principle stresses. Depending on the stress field prior to excavation, theshear stress close to the excavation can be sufficiently large for the stress path to enter thedomain of dilatants her deformation. Rapid radial de-stressing of the rock in the vicinity of anexcavation may also lead to localized extensile failure. Fractures formed in this way aresometimes referred to as unloading cracks. Regardless of the precise rupture mechanism,open fractures may be formed around excavations, leading to a region of enhancedpermeability known as the Engineering Damage Zone (EDZ).

The presence of an EDZ is acknowledged to be a particularly important issue in theperformance assessment for the disposal of radioactive waste. Interconnection of fractures inthe EDZ could lead to the development of a preferential flow path extending along theemplacement holes, access tunnels and shafts of a repository towards overlying aquifers andthe biosphere.

The size and the properties of the EDZ depend on the excavation method, the state of stress,the pore water pressure and the hydro-mechanical properties of the rock. Bedding planeanisotropy can be an important factor. In clays and argillaceous rocks, the most pervasiveforms of damage are caused by stress redistribution and unloading. Three basic forms offracturing may be defined: (a) shear fractures, (b) tensile fractures, and (c) extensile fractures.Recent experience during development operations in several Underground ResearchLaboratories clearly demonstrates that the dominant mode of fracturing can be quite different

from one mudrock to another. Examples from tunneling operations in the Boom Clay and theOpalinus Clay will be compared to show this variation.


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Can strain maps be used as an indicator for the extent of fault zone damage?

Shackleton, R., Bond C.E., Munro, L., Shipton, Z.K., and Seed, G.

Areas of damage around faults are of interest for their potential role as a barrier or conduit for

fluids and gases; thus, fault damage zones influence groundwater resources, hydrocarbonextraction and mineralisation, sub-surface waste disposal, and greenhouse gas storage.Consequently, predicting the geomechanical and hydrological properties of damage aroundfaults and the spatial distribution of these zones is a key question for applied geoscience.Previously, prediction of fault damage zone width has focused on fault length/displacementprofiles, which can be sub-grouped lithologically as a proxy for the geomechanical properties ofa given rock type. These studies give a wide spread in the observed scaling relationshipsbetween fault length and displacement. Here, we use strain maps produced by fully three-dimensional (non-plane strain) geomechanical restorations as a proxy for fault damage. Thegeomechanical algorithm restores displacement on faults while minimizing strain in thesurrounding surface using a mass-spring solver. Prescribed mechanical properties govern thebehaviour of the surface and therefore, the distribution of strain around faults. To evaluate theefficacy of the restoration in predicting fault damage, we compare the spatial distribution of

modelled strain to observed fault damage zones in well documented field examples of naturalreservoir analogues.


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Geometry, Kinematics, and Fracture Network Characteristics with Fault SegmentBoundaries, Wasatch Fault Zone, Utah, U.S.A.

Yonkee, W.A.1, Evans, J.P.

2, Bruhn, R.L.

3

1Department of Geosciences, Weber State University, Ogden, UT 84408-2507, U.S.A.

2Department of Geology, Utah State University, Logan, UT 84322, U.S.A.3Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112, U.S.A.

Structural boundaries divide most major fault zones into segments that have differentgeometries and often different rupture histories. Multiple directions of faulting are generallyrequired to transfer displacement across boundaries, resulting in development of complexminor fault networks and concentrated alteration. Such boundaries may act as sites of rupturenucleation or rupture termination, and be associated with microsesimicity between majorfaulting events. Here we describe characteristics of two structural boundaries in the activeWasatch fault zone of northern Utah: 1- the Pleasant View salient that separates the BrighamCity and Weber segments; and 2- the Traverse Mountains area that separates the Salt LakeCity and Provo segments.

The Pleasant View salient is marked by a major bend from northerly strike to ~315 within theboundary, an ~3 km left step in the main fault, and a structurally elevated, complexly faultedblock that continues SW in the subsurface. The footwall contains a damage zone of fracturedand altered quartzo-feldspathic gneiss. Fault-related rocks show a progression from olderchlorite breccia and minor phyllonite that likely formed at deeper levels, to microbreccia zones,to younger highly polished surfaces with well developed slip lineations. North of the boundary,the footwall damage zone is < 30 m thick and has relatively simple kinematics with mostly west-dipping normal faults. Within the structural boundary, the damage zone is >200 m thick andkinematically complex, with SW-dipping, SE-dipping, and NW-dipping faults that have mostly

normal slip (indicating 2~3).

The Traverse Mountains area is also marked by a major bend from a typical northerly strike to~ 270 within the boundary, and a complexly faulted hanging wall block (Traverse Mountains)

that continues to the WSW. The footwall contains a damage zone of fractured and alteredgranite that increases in thickness from ~ 20 m to the north to >200 m in the boundary. Faultrocks show a progression from chlorite phyllonite with plastic deformation of quartz that formednear the base of the seismogenic zone, to cataclastite zones with zeolite veins. Within thestructural boundary, the damage zone is >200 m thick and kinematically complex, with gently tomoderately SW-dipping, steep SE-dipping, and steep NW-dipping faults with normal to oblique

slip (indicating 2~3 along with temporal changes in stress).

Interaction of complex minor fault networks in boundaries may result in geometric hardening iffaults meet at high angles, or in geometric softening if faults meet at low angles with sliplineations parallel to their intersections. Preferred orientations of minor faults and fracturenetworks produce enhanced, anisotropic permeability, modulated by variations in mean anddeviatoric stress, and in reduced, anisotropic elastic moduli. Sealing of minor faults andfractures may strengthen the damage zone, whereas alteration of feldspar to mica andhydrolytic weakening of quartz weaken the zone.


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Characterization of fault damage zone and deformation band populations based onoutcrop data

S. Schueller1, A. Braathen

1,2and H. Fossen

2

1

entre for Integrated Petroleum Research, University of Bergen, Allgaten 41, 5007 Bergen,Norway2University Centre in Svalbard, 9171 Longyearbyen, Norway

Fault damage zones in porous sandstones contain small-scale structures, notably deformationbands, which may influence fluid flow in reservoirs. This study aims to characterize thegeometry of fault damage zone and especially the distribution of deformation bands using anoutcrop-based database. The bulk of these analogue data was gathered mainly in Utah andEgypt. Processing of 106 damage zone scanlines reveals a non-linear relationship between thedamage zone width and the fault throw. The results also indicate a logarithmic decrease indeformation band frequency away from the fault core as well as a fractal spatial distributionresponsible for the clustering of the deformation bands. Parameters such as the footwall andhanging-wall positions or the folding of the damage zone are also analyzed with regard to the

damage zone width and the deformation band density in the media. This database revealsseveral statistical trends that help to characterize damage zones of extensional faults insiliciclastic sedimentary rocks.

The trends derived from this analysis can be used to simulate statistically the growth of thedamage zone, and the evolution of deformation band populations. These probabilistic modelscan then be implemented in reservoir models in order to evaluate reservoir performance of faultdamage zones.


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Mechanics of fault-zone localisation in high-porosity sandstones and impact on flowefficiency

Christopher Wibberley1and Elodie Saillet

2

1

Total, CSTJF, Av. Larribau, 64018 Pau, France. e-mail: [email protected] Azur CNRS, Universit de Nice Sophia Antipolis, 250 rue A. Einstein, 06560

Valbonne, France e-mail: [email protected]

Excellent exposures of Cretaceous high-porosity sands and sandstones from the Bassin duSud-Est, France, allowed us to examine: (i) the role of tectonic loading path on cataclasticdeformation band network development; (ii) the development of larger ultracataclastic faultsduring deformation, and (iii) the likely impact of deformation bands and faults on flow efficiencyin high-porosity sandstone reservoirs. For a study area which had been subjected mainly to lateCretaceous shortening, a 250 m long outcrop recorded a persistent high density of reverse-sense conjugate deformation bands which did not appear to cluster around any mapped faults.For two study areas which had experienced significant Oligocene-Miocene extension, amoderate, undulating background density of normal-sense deformation bands was recorded,

which became focussed into clusters in places. Thus tectonic loading path and the nature of thestress changes causing deformation may strongly influence strain distribution. Largerultracataclastic faults and discrete slip planes are found localised within or at the edges of someof the deformation band clusters, demonstrably post-dating the deformation band cluster in onecase, but other clusters are present without larger faults within them. Hence these structuresformed by progressive localisation of deformation through deformation band clustering to formthe larger ultracataclastic faults, rather than in a damage zone which spreads with displacementincrease after fault initiation. Permeability measurements of these ultracataclastic faults suggestthat they may severely impact on flow efficiency during production of hydrocarbon reservoirs,and sub-seismic prediction of such zones is therefore critical to production management. Low-displacement deformation bands however, have a variable effect on flow efficiency but impactmost when produced by tectonic shortening.


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Strain accumulation and fluid flow in and around basin bounding fault zones of theLeichhardt River Fault Trough, Qld. Australia

J. G. McLellan, Predictive Mineral Discovery Co-operative Research Centre, EconomicGeology Research Unit, James Cook University, Townsville, Queensland, 4811, Australia

The Leichhardt River Fault Trough (LFRT) in the western Mount Isa Inlier, northwestQueensland, provides a good example of a relatively well preserved rifted basinal architecture,which allows a solid framework for rigorous testing of numerical scenarios in such a setting.The Pb-Zn-Ag and Cu mineral endowment of the Mount Isa Inlier is world-class, and thisprovides a strong foundation for current and future exploration in the region. To increase ourpredictive capacity we must try to better understand the early deformational influence (basindevelopment) over fluid pathways and fluid driving mechanisms. The LRFT has undergone aprotracted deformational history and here the deformation, fluid flow and mineralizationprocesses are addressed by several simulations in the numerical code FLAC3D. Duringextensional rifting, deformation is partitioned with major basin bounding structuresaccommodating the majority of the strain, areas of high shear strain, dilation and fluid flow arefocused in basin bounding structures, particularly in and around the western basin margin. This

focussing mechanism on the western basin margin is the result of a self-organised behaviourrelated to the asymmetry of the basin geometry. A thickening wedge to the west and abasement detachment zone which influences the distribution of strain within the upper crustalcomponents of the system. Extension and topography play an important role in facilitatingdownward migration of fluids deep into the system. Deformation induced dilatancy andtopography provide the required conditions suitable for brine reflux within the superbasins,which is an important process for mineralising systems. Later basin inversion facilitatespotential mixing of shallow basinal and deep seated basement derived fluids before migration todepositional sites primarily in the hanging-wall sediments of the Isa Superbasin. The hanging-wall sediments and intersections of N-S trending basin bounding structures and E-W trendingstructures are key areas for focusing shear strain, dilation, high cumulative fluid flux andpotential mineralization in the Leichhardt River Fault Trough, western Mount Isa Inlier.


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Structural and statistical analyses of fault-controlled hydrocarbon migration andaccumulation

*Agosta F. ([email protected]), *Alessandroni M., **Antonellini M., *Tondi E.*Dipartimento di Scienze della Terra, Universit di Camerino, Via Gentile III da Varano, 62032

Camerino (MC), ITALY**CIRSA, Centro Interdipartimentale di Ricerca per le Scienze Ambientali, Universit diBologna, Via Tombesi dall'Ova 55, 48100 Ravenna, ITALY

Excellent outcrops located within a hydrocarbon-rich quarry, cropping out along the northernside of the Majella anticline (Central Italy), allowed us to study both deformation mechanismsand hydraulic properties of normal-oblique faults. By combining large-scale geological mappingwith detailed structural and statistical analyses of their internal deformation, we were able toassess: (i) the mechanisms of fault initiation and fault growth within a carbonate grainstonesprotolith, (ii) the timing of faulting with respect to large-scale folding of the anticline, and (iii) therole played by faults (distinguished in small, medium, and large, respectively) and fractures inthe migrations and accumulation of hydrocarbons.

At a large scale, the oil show (the studied quarry) is located within an extensional relay rampbounded by two oblique normal faults. These large faults developed to a few km in length, andsolved up to 10s meters offset. Their internal architecture is comprised of inner fault coresmade up of brecciated and comminuted fault rocks and major slip surfaces surrounded bythicker damage zones. The latter zones are characterized by intense fracturing, dilation offavourably oriented pre-existing stylolites and sheared stylolites, and minor faults. Within thequarry, hydrocarbons in form of tar are largely present in the faults damage zones, and in theless deformed portions of the fault cores (breccia), as well as along some of the major slipsurfaces bounding these cores.

The whole extensional relay ramp is crosscut by several normal, oblique, and strike-slip faultsthat are classified as medium (1m < offset < 10m) and small faults (offset < 1m). Thearchitecture of medium faults is made up of inner fault cores, comprised of fragmented

carbonates and discontinuous slip surfaces that bound isolated blocks of fault breccias andcomminuted fault rocks, and outer damage zones that include stylolites, sheared stylolites,subvertical cracks and veins, and small faults. These small faults, conversely, rarely showpresence of inner fault cores. Their architecture generally consists of discontinuous bed-bounded slip surfaces, stylolites, sheared stylolites, and rare subvertical cracks and veins. Tardistribution shows that extensional jogs bounded by adjacent normal and oblique small andmedium faults represent the favoured sites for hydrocarbon migration.

The relations among the individual fracture characteristics (orientation, spacing, length, andopening) and tar distribution were statistically analyzed in the damage zones of the two largefaults. The results are consistent with the following conclsuions: (i) Hydrocarbon migration wasnot influenced neither by fracture density nor by fracture length. (ii) Field evidences suggestthat connectivity to, and distance from, nearby larger hydrocarbon conduits (e.g., slip surfaces)

played the most important role. These evidences are more pronounced in the hanging walldamage zones, probably due to the pronounced cracking that occurred in these zones. (iii)Fracture infilling, as well as fracture opening, were also affected by the current hmax acting incentral Italy. These conclusions will be tested soon by the results of well logs (acoustic,resistivity, and gamma ray data), core, and hydraulic analyses of the largest oblique normalfault (offset > 40m).


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Experimental modeling of extensional fault domains and fault-domain boundaries(transfer zones / accommodation zones)

Roy W. Schlische and Martha Oliver Withjack, Department of Earth & Planetary Sciences,Rutgers University, 610 Taylor Road, Piscataway, NJ 08854-8066, USA

([email protected]; [email protected])

Fault domains, in which all or most normal faults dip in the same direction, are common inmany extensional provinces. Fault-domain boundaries are zones that separate adjacent faultdomains, and are variously referred to as transfer zones or accommodation zones. We haveused experimental (analog) models of uniform extension to study the origin, geometry, andevolution of fault domains and their boundaries. Our models show that fault domains and theirboundaries develop with both orthogonal and oblique extension and with both dry sand and wetclay as the modeling material. The size and shape of the fault domains and the number andorientation of their boundaries is highly variable, even for identical models. Generally, fault-domain boundaries are broad zones of deformation, consisting of overlapping tips of normalfaults from adjacent fault domains, fault-displacement folds, and numerous small-scale normalfaults. The fault-domain boundaries in our models differ significantly from those in published

conceptual models of transfer zones / accommodation zones. Specifically, the fault-domainboundaries in our models are broad zones of deformation, not discrete strike-slip or oblique-slipfaults; their orientations are not systematically related to the extension direction; and they canform spontaneously without any prescribed pre-existing zones of weakness.

We infer that the fault domains in our models result from the self-organized growth of faultpopulations in which the stress-reduction zones of large, parallel faults are less likely to overlapand inhibit fault growth. The spatial arrangement of fault domains and their boundaries isgoverned by the spatial distribution and dip direction of the earliest formed large normal faults,the locations of which are, at least in part, controlled by a random distribution of flaws(nucleation points). Our models show that the presence of multiple fault domains affects thesize of normal faults because the length of an individual fault cannot exceed the fault-parallelwidth of its fault domain. Consequently, fault lengths are more likely to be constrained as strain

increases and fault domains interact. Additionally, although the fault population as a whole willshow a positive relationship between fault length and displacement, the displacement-lengthscaling relationship may change with increasing strain. The presence of fault domains maycontribute, in part, to the large scatter in length-displacement data observed for natural faultpopulations.


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Predictive Modelling of the Evolution of Fault Zone Structure: 3-D Sandbox and FieldScale Modelling

D.A. Thornton, Rockfield Software Limited, Technium, Prince of Wales Dock, Swansea, UKA.J.L. Crook, Rockfield Software Limited, Technium, Prince of Wales Dock, Swansea, UKJ.G. Yu, Rockfield Software Limited, Technium, Prince of Wales Dock, Swansea, UK

Predictive modeling of fault zone structure requires reconstruction of the stress anddeformation history using an integrated modelling framework that accounts for thesimultaneous evolution of the internal state of the rock formation due to the imposedboundary conditions. This necessitates the concurrent computation of displacement, fluidpressure and temperature history, together with the additional variables dependent upon thespecific physics included in the model.

This paper describes ongoing research on some of the key elements required for this class ofsimulation methodology and, in particular, presents predictive 3-D simulations of fault zonegrowth and discusses issues relating to the application of fully-coupled geomechanical andfluid flow models to field scale applications. Issues addressed include:

1 The strongly coupled nature of the mechanical deformation and the flow fields.

2 Algorithms for prediction of the onset and evolution of faults.3 Scale up from laboratory-scale sandbox tests to field scale models.4 Appropriate constitutive models for the evolution of the material state boundary surface.

This work is an extension of a previously published study (Crook et al., 2006a, 2006b) thatfocused on predictive modelling of structure evolution in sandbox experiments. Thecomputational approach adopts the Lagrangian finite element method, complemented byrobust and efficient automated adaptive meshing techniques, a constitutive model based oncritical state concepts, and global energy dissipation regularized by inclusion of fractureenergy in the equations governing state variable evolution. The modelling approach has beenbenchmarked by forward simulation of two extensional sandbox experiments that exhibitcomplex fault development. It is emphasized that no initial perturbations or fault seeding isimposed so that structure evolves solely from the prescribed movement on the basal

detachment.

In this study, simulations for compression and inversion tectonic regimes are briefly presentedbased on sandbox experiments investigating the evolution of doubly vergent thrust systems(McClay et al, 2004) and the evolution of inverted listric systems (McClay and Buchanan,1991). Simulations of 3-D extensional sandbox experiments performed by (Yamada andMcClay, 2003) will then be presented. These results, in conjunction with the previouslypresented extensional tectonic simulations Crook et al. (2006a), show that the model is ableto reproduce the experimentally observed faulting style in all three deformational regimes; i.e.the model is truly predictive.

The extension from laboratory-scale to field-scale necessitates coupling of displacement andpore pressure evolution together with an appropriate treatment of the complex constitutive

response. For example: (i) overpressure development; (ii) porosity reduction induced bymechanical and/or chemical compaction; and (iii) strengthening due to cementation, all alterthe position of the stress state relative to the state boundary surface, thereby either increasingor decreasing the likelihood of fault formation. It is shown that in order to capture thesemechanisms the constitutive model must trace the evolution of a state boundary surface thatis defined in terms of the complete stress tensor rather than being only dependent onporosity. While this class of model, formulated by extending critical state concepts, haspreviously been adopted by several researchers (e.g. Luo et al., 1998; Pouya et al., 1998;Dued et al., 2004), generally only mechanical compaction has been considered.Furthermore, most previous studies have focused on relatively simple sedimentationproblems which do not require the additional complex computational framework necessary torepresent evolving faults with large relative displacements.


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A field scale reconstruction with evolving fault architecture driven by tectonically inducedstress will be presented to illustrate the impact of differing assumptions for pore pressureevolution on the predicted fault architecture, and also highlight several issues related topractical field scale coupled geomechanical/flow modelling.


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References

Buchanan, P.G. and McClay, K.R. [1991] Sandbox experiments of inverted listric and planarfault systems. Tectonophysics 188, 97-115.

Crook, A.J.L., Willson, S.M., Yu, J.G., Owen, D.R.J. [2006a] Predictive modelling of structure

evolution in sandbox experiments. J. Struct. Geol. 28, 729-744.Crook, A.J.L., Owen, D.R.J., Willson, S.M., Yu, J.G. [2006b] Benchmarks for the evolution ofshear localisations with large relative sliding in frictional materials. Comp. Meth. Appl. Mech.Engng. 195, 4991-5010.

Deud, V., Dormieux, L., Maghous, S., Bathlmy, J.F., Bernaud, D. [2004] Compactionprocess in sedimentary basins: role of stiffness increase and hardening induced by largeplastic strains. Int. J. Num. Anal. Meth. Geomech. 28, 1279-1303.

McClay, K.R. [1990] Extensional fault systems in sedimentary basins: a review of analoguemodel studies. Marine and Petroleum Geology 7, 206-233.

McClay, K.R., Whitehouse, P.S., Dooley, T., Richards. M. [2004] 3D evolution of fold andthrust belts formed by oblique convergence. Marine and Petrol. Geology 21, 857-877.

Luo, X., Vasseur, G., Pouya, A., Lamoureux-Var, V., Poliakov, A. [1998] Elastoplasticdeformation of porous media applied to the modelling of compaction at basin scale. Marineand Petroleum Geology 15, 145-162.

Pouya, A., Djeran-Maigre, I., Lamoureux-Var, V., Grunberger, D. [1998] Mechanicalbehaviour of fine grained sediments: experimental compaction and three-dimensionalconstitutive model. Marine and Petroleum Geology 15, 129-143.Schneider, F., Hay, S. [2001] Compaction model for quartzose sandstones application to theGarn Formation, Haltenbanken, Mid-Norwegian Continental Shelf. Marine and PetroleumGeology 18, 833-848.

Wangen, M. [2001] A quantitative comparison of some mechanisms generating overpressurein sedimentary basins. Tectonophysics 334, 211-234.

Yamada, Y. , McClay, K. [2003] Application of geometric models to inverted listric faultsystems in sandbox experiments. Paper 1: 2D hanging wall deformation and sectionrestoration. J. Struct. Geol., 25, 1551-1560.

Yamada, Y., McClay, K.3-D Analog Modelling of Inversion Thrust Structures,in K. R. McClay, ed., Thrust tectonics and hydrocarbon systems: AAPG Memoir 82, pp. 276-301


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Influence of pre-existing fabric on normal-fault development: an experimental study

Alissa A. Henza1, Martha O. Withjack

1, Roy W. Schlische

1, Iain K. Sinclair

2

1Department of Earth and Planetary Sciences, Rutgers University, 610 Taylor Rd,

Piscataway, NJ 08854 USA2Husky Energy, Suite 810 Scotia Centre, 235 Water St., St. Johns, NL, Canada

Many rift basins have undergone multiple episodes of extension with differing extensiondirections. Do the normal faults that form during an early episode influence the developmentof normal faults that form during subsequent episodes? Does this influence depend on thecharacteristics of the early-formed faults (i.e., their number, density, length, displacement)?To address these questions, we have conducted a series of scaled experimental (analog)models with wet clay. Each model had two phases of distributed extension, and theextension directions during the first and second phases differed by 45. Because thecharacteristics of the fault populations at the end of the first phase depended on the totalmagnitude of extension, we incrementally varied the total magnitude of the first-phaseextension from 18 to 35%. As the magnitude of extension increased, the number, density,

length, and displacement of the normal faults that formed during the first phase alsoincreased. In all models, the total magnitude of extension was 35% during the second phaseof extension.

The experimental models show that the characteristics of the fault populations that formedduring the first phase of extension profoundly affected the fault patterns that developed duringthe second phase of extension. When the total magnitude of the first-phase extension wassmall (~18%), only a few short normal faults developed during the first phase. This poorlydeveloped fabric associated with these first-phase faults had little influence on thesubsequent deformation. Specifically, the normal faults that formed during the second phaseof extension had orientations, lengths, and displacements similar to those in models without afirst phase of extension. When the total magnitude of the first-phase extension was greaterthan ~20%, numerous large normal faults developed during the first phase, and they

significantly affected the subsequent deformation. Many of the first-phase normal faults werereactivated as oblique-slip faults during the second phase of extension. Additionally,numerous new normal faults developed during the second phase of extension. The second-phase normal faults were most likely to cut the first-phase normal faults when the magnitudeof the first-phase extension was small. Otherwise, most of the second-phase normal faultsnucleated at the first-phase faults or terminated against them. Generally, the second-phasenormal faults had anomalously short lengths compared to the first-phase faults, indicating thatthe presence of the first-phase faults had inhibited the propagation and growth of the second-phase faults. Interestingly, the orientations of the second-phase normal faults were bothorthogonal and oblique to the direction of the second-phase extension. This suggests that theformation of the second-phase normal faults was influenced by local perturbations of thestress state associated with first-phase faults.

The model fault patterns resemble those observed on 3D seismic data from the Grand Banks(e.g., Jeanne dArc basin), an area hypothesized to have undergone two non-coaxialextensional phases. Thus, the models may provide templates for interpreting the faultpatterns and interactions in the Grand Banks as well as other regions with multiple phases ofextension.


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Fault-surface corrugations: Insights f rom scaled experimental models of extension

Amber B. Granger, Haley & Aldrich, Inc, 299 Cherry Hill Rd, Suite 105, Parsippany, NewJersey 07054-1124, USA ([email protected])

Martha Oliver Withjack and Roy W. Schlische, Department of Earth & Planetary Sciences,Rutgers University, 610 Taylor Road, Piscataway, New Jersey 08854-8066, USA([email protected]; [email protected])

Many fault surfaces, observed in outcrop and 3D seismic data, have complex morphologieswith numerous corrugations that trend parallel to the slip direction. We have used scaledexperimental (analog) models with wet clay to study these features. Our models havesimulated extensional deformation (i.e., normal faulting) using three common basal boundaryconditions: two diverging, overlapping plates; a stretching, basal rubber sheet; and astretching, basal layer of silicone polymer. During the experiments, we photographed the topsurface of the models at regular time increments. After the experiments, we constructedstructure-contour maps for several normal-fault surfaces using closely spaced (1-mm apart)serial sections. The surface photographs, showing exposed fault scarps, and the structure-

contour maps, showing subsurface features, clearly demonstrate that the normal-faultsurfaces in all models are corrugated at various scales. The surface photographs indicatethat many of the large-scale corrugations formed during the linkage of originally separate faultsegments. The origin of small-scale corrugations, however, remains enigmatic. Thesecorrugations are subparallel to the slip direction, and are present along the entire extent of thefault surfaces. These observations suggest that the original small-scale corrugations are nottool-and-groove features because their lengths exceed the net slip. Furthermore, small,relatively isolated normal faults exhibit the same small-scale corrugations as larger normalfaults.

Experimental models with two non-coaxial phases of extension provide insight into the originof the small-scale corrugations. During the second phase of extension, many of the first-phase normal faults reactivate as oblique-slip faults. New small-scale corrugations develop

on the exposed fault scarps of these reactivated faults. These new small-scale corrugationsoverprint the original corrugations, are less well defined than the original corrugations, andare subparallel to the new slip direction. They are not related to fault propagation and linkagebecause they develop on pre-existing, through-going fault surfaces. Does the same processproduce the small-scale corrugations during the first and second phases of extension? Wehypothesize that the small-scale corrugations are related to incremental differential slip alongfault-segment surfaces, both during initial fault development and fault reactivation.


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Fault Facies modeling; poss ibilities and difficulties

Nttveit, H., Espedal, M.S. & Tveranger, J., Centre for Integrated Petroleum Research,University of Bergen, Norway

Depending on their internal structure and distribution of petrophysical properties, fault zonesmay act as barriers and/or conduits in subsurface reservoirs. However, our means forimplementing, and thus also quantifying the impact of 3D fault zone architecture on reservoirflow are limited by technical constraints of conventional modeling software.

The Fault Facies modeling concept offers a means for more realistic description of faults inreservoir models. By providing volumetric fault zone grids, all standard facies andpetrophysical modeling tools developed for sedimentary facies modeling, can be employed forfault zone modeling, facilitating explicit implementation of fault zone features as well as multi-phase flow properties. Uncertainty assessment also benefits from this approach, as thesedimentary and structural heterogeneities are treated equal.

The present work focuses on the property modeling when using the Fault Facies modeling

concept, emphasizing the representation of multi-scale multi-continuum fault properties inFault Facies models.Fault facies modeling of complex fault architectures is demonstrated for two fundamentallydifferent faults zones (carbonates and sandstones).

Fluid flow simulations performed on any scale require estimation of effective properties(upscaling). Upscaling is, however, complicated by the complex scaling relationships withinfaults. A nested local upscaling method is presented, giving improved realism to the estimatedeffective properties.

Faults in highly brittle rocks often involve high-permeable fracture networks. Simulating fluidflow in these faults require a dual-porosity approach. A dual-porosity model-setup isdemonstrated, and implications for upscaling are discussed.


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Using empirical geological rules to reduce structural uncertainty in seismicinterpretation of faults

Freeman, B.1, Boult, P.

2, and Yielding G.

1

1Badley Geoscience Ltd, Hundleby, Spilsby, United Kingdom.

2

Consultant, Adelaide, Australia.

Good seismic interpretation of faults should include a workflow that checks the interpretationagainst known structural properties of fault systems (a knowledge-based rule set). Estimatesof wall-rock strains provide one objective means for discriminating between correct andincorrect structural interpretations of 2D and 3D seismic data - implied wall-rock strain shouldbe below a geologically plausible maximum. We call this the strain minimisation approach.Fault population statistics from several dozen publications show that fault strike lengths andmaximum throws have a log-log distribution, their geometries are scale-invariant, and thatmaximum displacement on faults rarely exceeds 1/10 of their strike length. Interpreters canuse this knowledge base as a check for geologically plausible seismic interpretations. Byassuming that the maximum dip-dimension of faults is the maximum strike dimension, anupper limit of 0.1 can be placed on plausible wall-rock shear strain, and 0.2 for maximum wall-

rock longitudinal strain when measured in the displacement direction. Small-scale variation offault wall-rock strain also adheres to this rule, except in specific areas of strain localisationsuch as relay zones.

We present a case study where these simple rules provided a quantitative check on theplausibility of an interpretation. We reviewed an original structural model (interpretation of 2Dseismic surveys completed by a third party), and by mapping shear and extensional strain ontheir fault planes showed that the computed wall-rock strains for these parameters werecommonly above 0.1 and 0.2 respectively. Thus this third party structural model was verysuspect. We then reinterpreted the area in an iterative manner using the strain minimisationapproach. By using regions of implied high wall-rock strain as an indicator of high uncertaintyin the interpretation, we were able to break out two self-consistent faults sets, which hadgeologically plausible wall-rock strains, where previously there had only been one fault set

with highly implausible wall-rock strains. The new structural interpretation based on the 2Dseismic data was later found to be consistent with an interpretation of a nearby 3D seismicvolume that only became publicly available after the original work.


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Fault seal prediction of seismic-scale normal faults in porous sandstone: A case studyfrom the eastern Gulf of Suez rift, Egypt

Christian Tueckmantel1,2

, Quentin Fisher1, Rob Knipe

1,2, Henry Lickorish

3and Samir Khalil

4

1

Centre for Integrated Petroleum Engineering and Geoscience, School of Earth andEnvironment, University of Leeds, Leeds, LS2 9JT2Rock Deformation Research Limited, University of Leeds, Leeds, LS2 9JT

322 140 Point Drive NW, Calgary, T3D 4W3, Canada

4Geology Department, Faculty of Science, Suez Canal University, Ismailia, 41522, Egypt

A study of normal faults in the Nubian Sandstone Sequence, from the eastern Gulf of Suezrift, has been conducted to investigate the relationship between the microstructure andpetrophysical properties of cataclasites developed along seismic-scale faults and smalleroffset faults (deformation bands) found in their damage zones. This was to quantify theuncertainty associated with predicting the fluid flow behaviour of seismic-scale faults byanalysing small faults in core, a common procedure in the petroleum industry. Themicrostructure of the cataclasites was analysed as well as their single-phase permeability,

threshold pressure and grain-size distribution. Faulting occurred at a maximum burial depth of~1 km. Cataclasites delineate major slip surfaces and build up damage-zone deformationbands. Our results show that the lowest measured deformation-band permeabilities provide agood estimate for the permeability of the major slip cataclasites. This suggests that cataclasticpermeability reduction is mostly established early in the deformation history. Stress at thetime of faulting rather than final strain seems to be the critical factor. For viable predictions itis important that the slip cataclasites and deformation bands originate from the same host. Onthe other hand, a higher uncertainty is associated with threshold pressure prediction, as thelowest slip-cataclasite threshold pressure exceeds the highest deformation-band thresholdpressure by a factor of ~3. This may be due to microfractures introduced during exhumationor sampling, which bypass thin deformation bands but do not affect thick slip cataclasites.


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Structural analysis of the exhumed SEMP fault zone, Austria: Towards anunderstanding of fault zone architecture and mechanics throughout the seismogeniccrust

Frost, E., Dolan, J. F., Sammis, C.G., University of Southern California

Hacker, B., Cole, J., University of California at Santa BarbaraRatschbacher, L., University of Freiberg.

One of the most exciting frontiers in earthquake science is the linkage between the internalstructure and mechanical behavior of fault zones. Little is known about how fault-zonestructure varies as a function of depth, yet such understanding is vital if we are to understandthe mechanical instabilities that control the nucleation and propagation of seismic ruptures.This has led us to the Salzach-Ennstal-Mariazell-Puchberg [SEMP] fault system in Austria, amajor left-lateral strike-slip fault that has accommodated ~ 60 km of displacement duringOligo-Miocene time. Differential exhumation of the SEMP has resulted in a fault zone thatreveals a continuum of structural levels along strike. This provides us with a uniqueopportunity to directly observe how fault-zone properties change with depth, from near-surface levels, down through the seismogenic crust, across the brittle-ductile transition, and

into the uppermost part of the lower crust in western Austria. Here we present results fromfour key outcrops and discuss the mechanical implications of these new data.

Our brittle outcrop at Gstatterboden has been exhumed from at least 4 km depth. Here theSEMP juxtaposes limestone of the Wettersteinkalk on the south against dolomite of theRamsaudolomit on the north. Faulting has produced extremely asymmetric damage,extensively shattering and shearing the dolomite while leaving the limestone largely intact.We interpret this brittle damage using both mesoscopic calculations of damage intensity andmicroscopic grain-size-distribution analysis, and propose that strain has progressivelylocalized to a zone ~ 10 m wide. These findings are compared to those from two outcrops(Kitzlochklamm and Liechtensteinklamm) that bracket the brittle-ductile transition, exhumedfrom depths of 10 km. Here, the SEMP juxtaposes Greywacke Zone rocks on the northagainst carbonate mylonites of the Klammkalk to the south. We calculate the strain gradient

in the ductile Klammkalk rocks by analyzing the lattice preferred orientation (LPO) of calcitegrains throughout the outcrop. Deformation in the Greywacke Zone, however, contains asignificant component of solution mass transfer, and we therefore estimate the strain in theserocks by calculating the change in bulk volume. These analyses do not find significant levelsof strain distributed within the Klammkalk or Greywacke Zone, again revealing a highlylocalized fault zone.

Our investigation of the downward continuation of the SEMP into the Tauern Windowindicates that the fault remains discrete at mid-crustal levels, with the majority of strainoccurring in a 100-m-wide ductile shear zone (Cole et al., 2007). Combined with the recentwork of Rosenberg et al. (2007), who have studied the deepest exposures of the SEMP in thewestern Tauern Window, these data allow us to present a three-dimensional picture of faultzone architecture and mechanics from the top of the seismogenic zone all the way into the

ductile lower crust.


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Fault Facies methodology for systematizing analogue outcrop data to 3D fault g rids inreservoir models

Braathen1,2

, A., Tveranger1, J., Fossen

1, H., Schueller

1, S., Espedal1

1Centre for Integrated Petroleum Research, University of Bergen, Norway

2University Centre in Svalbard, 9171 Longyearbyen, Norway

Fault facies methodology aims on systematic description and representation of faultsobserved in nature. The approach has three steps; (i) establishing empirical relationships forfault zoning, (ii) applying facies classification schemes on structural elements in the zones,and (iii) assessing the systematic fault element characteristics by statistical analysis.Together, these steps define datasets that can be used to condition volumetric fault reservoirgrids.

The concept of fault facies encompasses the deformational products of any rock volumeaffected by faults. The presented facies database describes extensional faults in sand-shalesequences, with datasets from Sinai, Utah, Corsica, and Norway. The analogue database isorganized from the fault envelope downwards into core and surrounding damage zones, and

further into Facies Associations that consist of one or more Fault Facies. For example, theCore Architectural Element is commonly made up of various fault rock membranes, lenses,and fracture and deformation band sets. By considering for example lenses of host sandstoneas one Facies Association, several facies can be identified, based on the occurrence ofdeformation band sets within the lenses. Statistical analysis of the fault facies databaseestablishes dimensions, geometries and scales of various structural elements. Criticalassessments of length and width relations of core and damage zone reveal complementaryempirical trends that can be used in fault scaling considerations.

In total, fault facies modeling represents a powerful reservoir assessment tool. It opens forevaluation of fault-parallel flow, capillarity effects and communication between non-juxtaposedcells.


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What are the Potential Impacts of Low-offset Faults on Carbonate Reservoir Performance?

Susan M. Agar1, Stephan Matthai

2, Ravi Shekhar

1, Isha Sahni

1

1. ExxonMobil Upstream Research Company, Houston, TX 770072. Imperial College, London SW7 2AZ

Some of the world's largest hydrocarbon reservoirs are found in weakly deformed carbonate rocks atshallow crustal levels (< 5 km). The assemblages of fractures, stylolites and low-offset faults that aretypically found in these reservoirs can have substantial impacts on the flow behavior, even though thebulk strain is very low. Observations of outcrop analogs for these reservoirs in the Middle East and N.Africa, as well as seismic interpretations, indicate that many low-offset faults in carbonate rocks candevelop substantial vertical and lateral continuity (100 m - 1 km) even though their normal and strike-slip offsets are on the order of 0.5 m - 25 m. Other common characteristics of these fault zonesinclude: a segmented character with numerous small relay zones, clearly-defined, discrete fault slipplanes between segments, very limited or no fault gouge development, very limited or no damagezone development, incomplete cementation, alteration haloes and vuggy, karst / fault breccia-typeporosity.

The scale of continuity of these low-offset faults means that they can have significant impacts on flowperformance, acting either as conduits or baffles. If a low-offset fault acts primarily as a conduit, it canprovide pressure and fluid communication between different reservoir units that would otherwiseremain isolated by the lower-permeability beds between them. In this and the case of dominantlybaffling behavior, there may be substantial reductions in sweep efficiency. Consequently, these verysubtle faults are likely to have substantial economic impacts on hydrocarbon recovery.

Many of these faults are at or below the threshold for seismic resolution and core samples fromsubsurface fault zones are commonly not available. As a result, many assumptions for the specificarchitectures and mineralization of these faults are required for flow simulations. In an attempt tounderstand the sensitivity of flow behavior to these assumptions, preliminary, generic flowexperiments have been undertaken to determine how much difference changes to the low-offset faultarchitecture make to a flow prediction. Our initial results indicate that even with homogeneous matrix

properties the assumptions for the number of fault segments, the degree of overlap between thesegments and the extent of damage zone development can introduce substantial differences in flowpredictions for sub-km volumes of rock.

Recognizing the limitations of the modeling approaches used in these experiments, our preliminaryresults for water injection, suggest that subtle changes in the fault zone characteristics can makelarge differences in predicted times to water breakthrough. The results also reinforce the fact thatwhile well data provide information for a volume-averaged flow response, other approaches areneeded to gain insights to the impacts of specific geologic features on flow paths and velocities onproduction timescales. In this work, our aim is to develop a better understanding of the specific low-offset fault characteristics that have the greatest impact on the distribution of flow velocities in thereservoir. Through this approach, we aim to improve strategies for hydrocarbon recovery and historymatching.


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KEYNOTE:

A geometr ic model for the development of fault zone and fault rock thicknessvariations

Conrad Childs1, Tom Manzocchi1, John J. Walsh1, Christopher G. Bonson2, Andrew Nicol3,Martin P.J. Schpfer

1

1Fault Analysis Group, University College Dublin, Dublin, Ireland

2SRK Consulting (UK) Limited, Cardiff, UK, CF10 2HH

3GNS Science, Lower Hutt, New Zealand.

The thicknesses of fault rock and fault zones and the fault normal separations for intact andbreached relay zones each show a positive correlation with fault displacement. Thedisplacement to thickness ratio for these different structures increases from intact relay zones(median value = 0.28) to fault rocks (median value = 50). The frequently recorded positivecorrelation between fault displacement and fault rock thickness is often interpreted as agrowth trend controlled primarily by fault rock rheology. However recognition of similar

correlations for the other fault components suggests a geometrical model may be appropriate.In this model a fault initiates as a segmented array of irregular fault surfaces. As displacementincreases, relay zones separating fault segments are breached and fault surface irregularitiesare sheared off, to form fault zones containing lenses of fault bounded rock. With furtherdisplacement these lenses are progressively comminuted, and ultimately converted to zonesof thickened fault rock. The final fault rock thickness is therefore influenced strongly by faultstructure inherited from the geometry of the initial fault array. The model is one of progressivestrain concentration within a zone within which the active fault surface progressivelyapproaches, albeit along a potentially complex path, a more planar geometry. The large scalerange on which fault segmentation and irregularities occur provides the basis for applicationof this model over a scale range of 8 orders of magnitude. The model is consistent withoutcrop observations of the internal structure of fault zones, the large variations in fault rockthickness observed for a given displacement and with recently developed discrete element

models of fault zone evolution.


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KEYNOTE:

How granulated/cracked fault border zones, and their pore fluids, interact w ithearthquake rupture dynamics

James R. Rice, Department of Earth and Planetary Sciences, and Division of Engineering andApplied Sciences, Harvard University, Cambridge, MA 02138

Recent contributions on fault zones include insightful field characterizations of their finestructure, new laboratory experiments that reveal response in rapid and/or large slip, and newtheoretical concepts for modeling. The purpose of this talk is to review those newperspectives, particularly those relating to damaged fault border zones and the fluids whichthey host, and their impact on how we think about earthquake rupture dynamics.

Maturely slipped faults show a generally broad zone of damage by cracking and granulation,but nevertheless suggest that shear in individual earthquakes takes place with extremelocalization to a long-persistent slip zone, < 1-5 mm wide, within a finely granulated,ultracataclastic fault core. Relevant fault weakening processes during large crustal events are

therefore likely to be thermal and, given the damage zones and geologic evidence of water-rock interactions within them, it seems reasonable to assume pore fluid presence.

It is suggested that there are two primary dynamic weakening mechanisms during seismicslip, both of which are expected to be active in at least the early phases of nearly all crustalevents. Those are (1) Flash heating at highly stressed frictional micro-contacts, and (2)Thermal pressurization of fault-zone pore fluid. Both have characteristics which promoteextreme localization of shear. At sufficiently large slip, macroscopic melting will occur in casesfor which those processes have not efficiently enough reduced heat generation, and thuslimited temperature rise. Thermally driven decompositions may instead occur in lithologiessuch as carbonates and, in silica-rich lithologies, formation of a thixotropic gel-like layer maycontribute to weakening at large slip.

Theoretical modeling based on mechanisms (1) and (2), as constrained with lab-determinedhydrologic and poroelastic properties of fault core material and high-speed friction studies,suggests that earthquakes on mature faults might be plausibly described by thosemechanisms. Results suggest that faults may be statically strong but dynamically weak undertypical seismic conditions. Such allows major faults to operate under low overall drivingstress, with realistic seismic stress drops, a self-healing rupture mode, low heat outflow, andan absence of shallow fault melting.

Another source of dynamic weakening, at least in mode II slip, comes from contrast acrossthe fault of far-field elastic stiffness and density of the bordering crustal rock. Recent work hasshown that contrast across the fault of permeability and poroelastic properties within fluid-saturated damage fringes along the fault walls has an analogous effect. Both allow forreductions of effective normal stress during suitably directed non-uniform slip, like at a rupture

front, although the "preferred" rupture direction based on one effect may either align with, ormay oppose, that based on the other.

Other new perspectives in recent work involve understanding the interaction of rupture withoff-fault damage (branches, damage zones) and the induction of off-fault plasticity, togetherwith their interaction back onto rupture dynamics. As examples, in some cases the transitionto supershear may be suppressed, or at least ling delayed, by plasticity and, for dissimilarmaterials, the inclusion of elasticity can reverse an elastically preferred direction.


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The effect of the intermediate principal st ress on shear band strike and dip in thesilts tone straddling the active Chelungpu Fault, Taiwan

Bezalel Haimson1and John Rudnicki

2

1University of Wisconsin, USA

2

Northwestern University, USA

The Taiwan Chelungpu-fault Drilling Project (TCDP) was initiated in order to investigate therupture mechanism of the 1999 disastrous Chi-Chi earthquake (Mw 7.6). Two adjacent (40 mapart) scientific boreholes were drilled, which intersected the fault at about 1120 m andreached depths of 2000 m (hole A) and 1400 m (hole B). We conducted true triaxialcompression tests in the Pliocene Chinshui siltstone, which hosts the Chelungpu fault.Rectangular prismatic specimens were prepared from three cores, one from the hanging wall(depth of 891 m) in hole A, and two from the footwall (1251 m in hole A and 1285 m in holeB). Specimens were subjected to constant least (3) and intermediate (2) principal stressesand an increasing maximum principal stress (1) until brittle failure occurred (at 1,peak) inthe form of a shear band or fault. Several sets of experiments were conducted, each for afixed 3, and a 2 that was kept constant during testing but was varied from test to test

between 2 = 3 and 2 1,peak. Minor differences were observed between the two coresfrom hole A, and more substantial ones between the two footwall cores in holes A and B(Haimson et al, 2008). However, all tests showed a consistent pattern of significant increasein 1,peak as 2 was raised above the fixed 3, in contrast to predictions based on the Mohr-Coulomb condition that neglects the intermediate principal stress effect. Similar increases inelastic modulus and onset of dilatancy were also discerned. Some of the more importantobservations were related to the induced faults attitude.

Upon reaching 1,peak, specimens invariably develop a through-going shear band or faultthat strikes subparallel to 2 direction and dips steeply in the 3 direction. Measurementsrevealed that fault dip angle () decreases monotonically with increasing 3 for a constant 2,and increases monotonically with 2 for fixed 3. This variation of with intermediateprincipal stress is inconsistent with Mohr Coulomb theory, which asserts that the angle should

be independent of 2. The observations do indicate that for constant 3 fault dip angleincreases as the deviatoric stress state parameter (N) varies from for axisymmetric

compression (2 = 3) to for axisymmetric extension (2 = 1). The increase of withdecreasing N is consistent with the Rudnicki and Rice (1975) prediction based on shearlocalization theory using a Drucker-Prager (two invariant) type material relation. Sameexperimental data show a decrease in with increasing mean stress ( = ( 1+ 2 + 3)/3).In the plot of observed fault angles as a function of mean stress () the line fit for pure shear(N = 0), yields predictions for that are lower than observed; the line fit for axisymmetric

compression (N = ) yields predicted fault angles that are higher than observed. Despitethe discrepancy between the two predictions, the results are consistent with the observeddependence of fault dip angle on 2, which is not inherent in Mohr-Coulomb theory.


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Geomechanical sensitivi ty of reservoirs from statistical correlations of f low rates

John Greenhough1, Kes Heffer

2, Ian Main

1, Xing Zhang

3, Nick Koutsabeloulis

3

1University of Edinburgh

2Reservoir Dynamics Ltd.

3

Schlumberger Reservoir GeoMechanics Center of Excellence

While conventional reservoir modelling neglects geomechanical effects, there exists growingevidence that they play a key role in fluid flow. Coupled modelling of geomechanics and flowsupports the possibility of fault reactivation via changes in fluid pressure and temperature,andsuch faults are likely to have considerable influence on flow paths. Furthermore, recentdevelopments in statistical techniques highlight flow correlations that are not only long-rangebut related to faults and stresses; knowledge of all these characteristics is therefore of greatpotential value in reservoir management. Using various North Sea fields as examples, wepresent a novel, parsimonious model that identifies only well-pair correlations of the higheststatistical significance, combined with a geomechanical model, and suggest ways in whichthese tools might be integrated with other management processes.


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Excavation induced fractures in a plastic clay formation: observations at the HADES URF

Philippe Van Marcke, Wim Bastiaens, EIG Euridice, Boeretang 200, 2400 Mol, Belgium

The geological disposal of radioactive waste has been studied in Belgium since the earlyseventies by the Belgian Nuclear Research Center (SCKCEN). The research is focused onthe Boom Clay layer: a poorly-indurated clay that is found from a depth of 190 metres underthe site in Mol where it has a thickness of about 100 metres. It displays a plastic behaviourwhich results in self-sealing properties and a relatively high convergence when excavatinggalleries at depth. The hydraulic conductivity is in the order of 10

12m/s.

In 1980 SCKCEN started the construction of an underground research facility HADES. Itspurpose was to examine the feasibility to construct a repository and to provide SCKCEN withan underground infrastructure for experimental research on the geological disposal ofradioactive waste. Not much knowledge and experience on excavating galleries in a deepplastic clay formation was available at that time. The evolution of excavation techniques andgeomechanical understanding throughout time is reflected in the successive excavationphases of HADES. By the later construction of a second shaft and new galleries by industrialtechniques (1997-2007) the feasibility to build an underground repository in the Boom Clayhas been demonstrated.

In 2002 the second shaft was linked to the existing underground infrastructure by theconnecting gallery. Several measurement and research programmes were carried out before,during and after the construction works. The fracture pattern in the clay massif wassystematically observed. The focus was on shear planes, recognisable by their slickensidedsurface. The fracture pattern consisted of two conjugated fracture planes: one in the upperpart dipping towards the excavation direction, the other in the lower part dipping towards theopposite direction. The distance between fractures is a few decimetres and they originate atabout 6 metres ahead of the front. Borings performed shortly after the construction of thegallery revealed the presence of fractures up to a radial extent of 1 metre into the clay. The

orientation of the observed fracture planes could be explained by the stress state around thegallery.

In addition laboratory measurements and numerical modelling were performed to characterisethe geomechanical behaviour of the clay and to assess the impact of the excavation on theclay massif. Several European Commission projects were dedicated to this subject:SELFRAC, TIMODAZ and CLIPEX. The impact is probably limited by the sealingmechanisms that have been evidenced by laboratory measurements. Furthermore it has beenevidenced that the behaviour of the Boom Clay is characterised by a strong hydromechanicalcoupling, already noticeable at an unexpectedl

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Fault Zones Abstract Book