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Fourth International Conference on Fault and Top Seals
- Conference date: 20 Sep 2015 - 24 Sep 2015
- Location: Almeria, Spain
- ISBN: 978-94-6282-164-4
- Published: 20 September 2015
1 - 50 of 55 results
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A Post-mortem Study on Fault Retention Capacity
Authors R. Castilla and J. Huyghues DespointesThe main objective of this study is to test the methodology of retention capacity by capillary sealing. In order to accomplish this, we have chosen to study a prospect compartmentalized by faults already drilled by several exploration-appraisal wells simulating, as good as possible, the original exploration conditions before drilling. The predictions of the fault retention capacity study are coherent with the well results proving the reliability of the methodology. Results from wells confirm the predictions from the methodology. All drilled wells have found different OWCs and different pressure regimes of the oil columns. The inherent heterogeneities of the stratigraphy must be incorporated in the definition of faults-horizons intersections. The definition of Top and Base reservoir proved to be insufficient. The predictions became reliable only when a more refined stratigraphic model was incorporated into the prediction process.
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An Innovative Approach for the Prediction of Column Heights in Multi-fault Traps Using Deterministic Fault Seal Analysis
By P.G. BretanThe deterministic method for predicting column heights in traps involves constructing a fault framework model and populating the model with attributes. Shale Gouge Ratio (SGR) is calculated at sand-on-sand juxtapositions and transformed to hydrocarbon column height. The application of the deterministic method is straightforward for traps defined by few faults. Fault-plane sections are inspected visually to identify the column height that could be supported at the fault. However, for traps bounded by multiple intersecting faults identifying column heights through the visual inspection of fault-plane sections is practically impossible. A new automated approach is described that enables leak points and column heights to be quickly derived and evaluated for traps bounded by multiple intersecting faults. Fault 'side walls' defined by branch lines are simultaneously interrogated to derive a unique location of the leak point. The leak point is that point on a fault side wall which, when trappable column heights are calculated, implies the shallowest hydrocarbon contact in the trap. The new approach has shown that the location of a leak point in a trap can depend upon the transformation used to convert SGR to capillary pressure and has important implications for migration studies in complex fault-bounded traps.
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Integrated Fault and Top Seals Study in South Sumatra Wrench Basin
By P. AriyantoThe overprinting of pre-Tertiary structures and Paleogene rifting has created a series of half-graben with NE-SW and N-S trends in South Sumatra Basin. Plio-Pleistocene wrench tectonic then uplifted the basin and creating traps as well as promoting hydrocarbon migration (and leakage) through faults and weakness point of capillary seal. Despite the proven hydrocarbon fetching area and migration focal point, trapping mechanism in Rimau Block still becomes a challenging factor. This paper is aimed to evaluate the main factors that controlling trap and seal quality, which consist of: (1) Structural evolution, (2) Capillary entry pressure, and (3) Caprock/seal facies. Kinematic restoration was applied to reconstruct basement movement in the rift stage as well as inversion characteristic responsible for Plio-Pleistocene petroleum entrapment. Moreover, careful evaluation about the connection between seal depositional setting and MICP measurement was made in order to understand the involvement of fault and lateral stratigraphic seal on petroleum seal capacity. The identification and application of the seal integrated study is expected to minimize risk and improving volumetric calculation criteria for future exploration and development projects.
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Geomechanical Assessment of Flow Barriers Observed from 4D Time-lapse Survey for CO2 Storage in Snøhvit Field
Authors J.C. Choi, E. Skurtveit, B. Bohloli and L. GrandeThis study assesses the characteristic of flow barriers observed from 4D time-lapse survey for CO2 storage in Tubåen Formation, Snøhvit field by geomechanical analysis. The flow barriers are hypothesized as structural compartments (e.g. sub-seismic faults) and then the stability of faults are assessed by both numerical and analytical approaches. The analytical approach results in stable condition of hypothetical sub-seismic faults. However, stability seems to be underestimated mainly due to simplified assumption of the analytical approach. The numerical approach estimates failure of flow barriers that can cause communication even outside the flow barrier, which seems to be inconsistent with the seismic 4D observation. The numerical estimation may imply that the observed flow barrier is a feature of depositional flow channel rather than a structural compartmentalization. However, the assessment was carried out based on conservative scenario. Further work on realistic implementations of complex fault structure into the analysis would be important for better assessment of fault integrity and characterization of flow barrier.
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The Effect of Fluid Flow in Relay Ramps on Seismic Images
Authors C. Botter, N. Cardozo, I. Lecomte, A. Rotevatn and G. PatonUsing an integrated workflow from an outcrop model in the Arches National Park, Utah, fluid flow simulation to seismic modelling, we intend to study the impact of a relay ramp system and its fluid composition on seismic images. Faulting in porous sandstone is associated to deformation bands that decrease the porosity and permeability locally. Based on those modified petrophysical properties, we run a fluid flow simulation and a ray-based pre-stack depth migration (PSDM) simulation to evaluate the impact of parameters such as illumination or wave frequency. We study the relay ramp at two stages of the fluid flow simulation: at the beginning and at the end. Only the changes in porosity around the faults are visible at the beginning, while fluid contacts affect also the model at the end. Resultant seismic images are able to show reflection and diffraction for the two faults when constant fluid saturation at the beginning. However, the thin layer of water at the top of model has a much stronger impact at the end and the faults can hardly be interpreted. Our methodology provides ways to better understand how faulting impact seismic, and therefore to tune acquisition and processing parameters for fault characterization.
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Application of Seismic Attribute Volumes for Detailed Interpretation of Fault Interactions and Growth
Authors H. Joergensen and B. AlaeiThe aim of this study is to correlate outcropped-based knowledge of fault interaction, linkage and growth to seismic fault attribute volumes. This ended up in a better understanding of seismic attribute variations and improved the reliability of interpretation. Advanced fault imaging using seismic attributes has substantially improved imaging of fault characteristics. Utilizing 3D seismic attributes, we followed the fault interaction related structures through different geological layers, which is otherwise hard to follow on outcrop. The present study illustrate the importance of using applications of seismic attribute volumes for detailed interpretation of fault interaction and their evolution through time. This study also provides criteria for more quantitative interpretation of fault attribute volumes instead of just geometrical observations in 3D. Finally, this study propose that the magnitude value of attribute volumes (fault enhance) provides a relationship to the intensity of deformation related to fault interaction.
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Relationships between Overburden Brights and Leakage from Underlying Reservoirs in the Barents Sea
Authors C. Hermanrud, T.H. Simmenes, R.A. Ersland and L. GeorgescuAnalyses of hydrocarbon-related bright amplitudes in overburden rocks have demonstrated that such amplitude anomalies can often be associated with gas leakage from faults or fault intersections that offset underlying reservoirs. The position of the gas water contact frequently coincides with the depth of the top reservoir surface where it is intersected by the faults. The acoustic expression of the leaked gas differs significantly among areas, and is largely controlled by the caprock lithology.
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Fault-seal Risk Analysis for CO2 Storage in the Petrel Sub-basin, NW Australia
Authors G. Yielding, C. Consoli and P. BoultThis geomechanical analysis of the faults in the Petrel sub-basin, NW Australia, aimed to constrain the in-situ stresses and rock strength and to evaluate the risk of fault reactivation and leakage. The risk of reactivation (in terms of stress ratios such as Slip Tendency) was highest on faults orientated in an approximately east-west direction. However, a fault intersecting a shallow reservoir has a lower stress state and requires a smaller increase in pore pressure to induce failure (Slip Stability), even if not optimally oriented. Pore-pressure increases during CO2 injection of <5MPa could therefore potentially cause leakage up those faults in the shallowest eastern part the study area. The broader basin prospectivity assessment, of which this study is only a part, has found that within the western areas of highest potential for CO2 injection and storage the risk of failure along identified faults is low. Furthermore, injection simulation modelling has shown that pore-pressure under typical injection conditions and parameters would not approach the pressure required to cause fault leakage.
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Preliminary Analysis of Containment Integrity for Geological Storage of CO2 at the South West Hub Project, Western Australia
Authors L. Langhi, Y. Zhang, B. Ciftci, C. Delle Piane, J. Strand, D. Dewhurst, L. Stalker and K. MichaelThe Mandurah Terrace in the onshore Perth Basin was proposed as a suitable site for CO2 injection. Prior investigations in the area indicate that faults affect the target storage reservoir and shale barriers. Changes in the pore pressure and stress field induced by fluid injection could alter the containment integrity by either exceeding fault capillary resistance or by triggering slip on pre-existing faults. The capillary properties of faults have been assessed using the Shale Gouge Ratio predictive algorithm which can assess the maximum fluid column height trapped by a fault without leaking. Three different scenarios were investigated, representing different juxtaposition geometries. In the south of the area, potential spots for local up and across fault fluid migration are noted. The relationship between the modelled faults and the present-day stress field has been investigated to define critically stressed fault segments most at risk of reactivation resulting from pore-pressure build-up due to injection. The likelihood of fault reactivation is low in the current day stress field with pore pressures required equivalent to a CO2 column exceeding 1000m. Preliminary geomechanical modelling also shows no likelihood of fault reactivation and potential ground uplifts of less than two centimetres at the surface.
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Keynote Speech - Hydrodynamic Constraints on Fault Seal Analysis - Linking Capillary and Fault Reactivation Processes
More LessThe overarching goal of fault zone analysis is to accurately estimate fault mechanical and hydraulic properties that may influence the connectivity either across a fault or along a fault and between reservoirs under variable stress conditions. Fault seal capacity is the term used to describe the ability of the fault to impede the migration of one or more fluid types under certain stress constraints. Academics and industry technologists have developed a number of techniques for assessing various physical characteristics of faults and these have often been grounded either in outcrop analogues or observations of faults in the subsurface thought to be either trapping hydrocarbons or showing evidence of breach. These techniques tend to be process specific, targeting fault rock strength, reactivation potential, across fault capillary seal capacity, or up-fault leakage potential. After examining these various components individually a holistic fault seal analysis can be assembled.
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Relating Structural Elements to Cross-fault Flow - Implications for Fault Permeability Estimation
Authors M. Kettermann, J.L. Urai and P.J. VrolijkThe evolution of cross-fault fluid flow in sand-clay sequences, especially the role of structural elements is not well understood. We present observations from analogue experiments using an underwater sandbox setup that allows dynamic cross-fault flux measurements. We combine the results of flux measurements with observations of the evolving fault zone in map view as well as with structural information of the clay smear after completing deformation. Carefully excavating the clay smear allows finding holes in the clay as well as relays, horses and other structures. Clay veneers of ~0.1 mm remain intact during the excavation process. We present results of eight experiments with the same total clay volume, of which three experiments had two clay layers with each half the thickness of the other experiments. The results show a more linear evolution of flux with smaller total flux. In experiments with a single clay layer we interpret the initial deformation to be hybrid failure with sudden increase of flux while at later stages fault segmentation and shearing of clay fragments causes less distinct increases of flux. Finally, we observe a process potentially capable of resealing discontinuous clay smears.
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Deformation Bands in Chalk and Their Impact on Fluid Flow - An Example from Pegwell Bay, Kent
Authors I. Kaminskaite, Q.J. Fisher and C.A. GrattoniCompactive faulting was systematically investigated on highly porous chalk containing deformation bands from Pegwell Bay. The pore grain radius, porosity, and Klinkenberg-corrected gas permeability were determined for both deformed and undeformed rock. CT-scans show a decrease in porosity by more than 10% in deformation bands compared to the associated undeformed chalk. Microstructural analysis suggests that the porosity reduction occurred due to the collapse of fossils that contained macroporosity. The gas permeabilities range from 0.9 mD to 3.1 mD for the core plugs containing deformation bands and from 1.8 mD to 2.8 mD for the core plugs of the host rock. Mercury injection analysis show that there is considerable overlap between the pore size distribution and threshold pressures of the undeformed chalk and the samples containing the deformation bands. Permeability and threshold pressures are not significantly affected by the presence of the deformation bands because the destroyed macroporosity did not form a connected network.
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Permeability Estimation in a Multi-fractured Top Seal
Authors R.E. Rizzo, D. Healy and L. De SienaPermeability of fracture media is one of the most important parameters characterising fluid flow, but it requires a detailed knowledge of fractures and fracture networks distribution. The unique exposures north to Santa Cruz represents a rare opportunity to observe and fully investigate a recently active bitumen-bearing fractured top seal. Permeability of a fracture network depends on the statistical distribution of fracture length, aperture, orientation, and density. Those fracture attributes are related to the permeability properties though a tensor (the Permeability Tensor). The statistical methods presented here for collecting and analysing fracture attributes shows how to obtain a more accurate data set directly collecting fracture attributes from fields, and how those features are fundamental for estimating permeability in a multi-fractured system.
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Shallow Gas Offshore Netherlands - The Role of Faulting and Implications for CO2 Storage
Authors J.D.O. Williams and C.M.A. GentThe presence of shallow gas within Pliocene–Pleistocene sediments in the North Sea is well known, though there is still some debate regarding its origins. Many of the shallow gas accumulations are coincident with faults developed over salt structures, leading to speculation that faults may have acted as conduits for upward migration of hydrocarbons from greater depths. The role of faults in charging of the Pliocene–Pleistocene reservoirs is investigated for several of the gas accumulations through interpretation of 3D seismic reflection data, revealing the relationship between faults and seismic indications of gas saturated sediments such as bright spots and gas chimneys. In order to invoke the faults as migration conduits for the gas, they must form part of the migration pathway between the gas-charged sediments and thermogenic source rocks. For the accumulations studied, such migration routes exist with salt-withdrawal beneath mini-basins allowing Carboniferous-sourced gas to migrate to the Triassic, and subsequent vertical migration along faults and fractures associated with diapirism. The faults in question are near critically-stressed, and have been active in the recent geological past. The observation of shallow gas seemingly associated with such features may have implications for the sequestration of carbon dioxide in formations affected by similar features.
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Clay Smear Processes in Unlithified Clay-sand Sequences of the Hambach Lignite Mine
Authors M. Kettermann, J.L. Urai, S. Thronberens and S. AsmusClay smears are highly variable three-dimensional structures and the controlling factors are still poorly understood. We present an outcrop based study in unlithified sand-clay sequences of the Hambach open-pit lignite mine, Germany. With the help of an excavator we dug four trenches across a fault with up to 1.5 m displacement. In cross-sections we could study clay smear thicknesses distributions and related host rock deformations (R- and R'-shears). Incremental slicing of cross-sections allowed the creation of a 3D thickness map showing that the thickness of the clay smear is not related to the down-dip position along the fault. Other sections showed that holes in the clay smear are the result of shear bands cross-cutting the clay smear rather than of strain thinning. Furthermore we show the importance of grain-scale mixing on clay smear thickness and continuity. In multilayer sequences a wide shear zone causes the formation of a continuous sand-smear between clay smears, forming an effective up-fault fluid pathway. Excavated clay smear surfaces show the variety of structures forming the smear including re-sheared clay fragments and clay-noses with the potential to thicken the clay smear and reseal discontinuous smears.
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Modeling of Stress and Pressure Dependence of the Sealing and Transport Properties of the Fault
By A.Y. RozhkoFaults (shear cracks) are formed by the coalescence of tensile microcracks in the brittle caprock. The damage zone of the fault consisting of microcracks can serve as a permeable pathway within sealing formations. Like macrofractures, microfractures occur in populations that exhibit well-defined statistical properties such as their size distribution. The are many publications explaining how the aperture size distribution can be related to the sealing and transport properties, described by capillary pressure and effective phase permeabilities, however there are no models which explain how the aperture distribution depends the effective confining stress and on the saturation degree. Available models, developed for porous rock are not applicable to fractured rock, because fracture is much more compressible than the pore throat. In this paper the author proposed a new theoretical model, applied in two steps to the damage zone of the fault. In the first step the author developed new analytical solutions for the effective phase permeabilities and capillary pressure of the rock possessing a single deformable crack. In the second step the author applied the analytical solutions to multi-scale microcrack system of the damage zone of the fault to predict the stress and pressure dependence of the sealing and transport properties of the fault.
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Permeability Heterogeneity in Fault Damage Zones and Its Relationship to Deformation Band Connectivity
Authors P. Edwards, D.J. Sanderson and Y.S. KimWe calculated the width of a connected deformation band volume, or ‘effective damage zone’ using proportion of connecting nodes in the damage networks, and calculating the distance from the fault at which the network is not connected. The geometry of deformation bands in the damage zone (parallel strike to the fault) results in directional differences in fluid flow reduction through the networks. Fault normal flow would be reduced significantly more than fault parallel flow through connected deformation band networks, only if the deformation bands were connected. An increase in the proportion of deformation bands to matrix, moving towards the fault, along with increases in connectivity would result in very low fault normal permeability within the effective damage zone.
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Cataclastic Faulting and Cementation Interplay in Shallow Porous Sandstones - Insight from a Groundwater Context
Authors S. Philit, R. Soliva, P. Labaume and C. GoutThe understanding of the interplay between fault zone cataclasis and cementation is important since both processes can reduce the permeability of faults in porous sandstones significantly. The case of fault cementation in high-porosity sandstone reservoirs at shallow depth (<2 km; T° <80° C) has almost never been investigated. The macro- and microscopic analysis of a fault zone in the porous Cenomanian quartz arenite sands of Provence (France) shows that silica diagenesis occurs in the most intensely deformed cataclastic parts of the fault zone. This fault zone contains clusters of shear bands and 19 to 48% of its thickness is occupied by low-porosity silicified cataclastic structures. The analysis of the alteration profile around the fault zone reveals the presence of groundwater silcretes in the form of tabular, tightly silicified sandstone bodies. Cold-cathodoluminescence microscopy analyses of the silica cements (of the fault and the silcrete) tend to confirm the groundwater origin of the silica cements from diagenetic processes. This study therefore shows that silica cementation can occur in a fault zone in a shallow context of groundwater silcrete. Consequently, its sealing capacity could be acquired potentially early in the burial history of a sandstone reservoir.
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Seismic Imaging of Fault Facies Models – A Pilot Study
Authors D. Kolyukhin, V. Lisitsa, D. Qu, M. Protasov, V. Tcheverda, J. Tveranger and D. VishnevskyOur study focusses on seismic analysis of fault damage zones. A model containing a fault zone populated with fault facies is used as input to seismic forward modeling and imaging. A statistical comparison of the geological input model and the resulting seismic images was carried out, and the link between fault zone model parameters and seismic resolution studied. Our study demonstrates the potential of systematically using detailed geological 3D models of fault zone structures and properties to understand seismic responses from subsurface fault zones.
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The Role of Mechanical Anisotropy in Controlling Fault Trajectories within Multilayered Carbonate and Clay-rich Rocks
Authors C. Giorgetti, B.M. Carpenter, M.M. Scuderi, T. Tesei, M.R. Barchi and C. CollettiniThe mechanical stratigraphy of multilayered carbonates and clay-rich rocks may have a major influence in petroleum system, since marly horizons potentially act as top seals. Faults affected these heterogeneous lithology show complex geometries. We here investigate, through structural field analysis and laboratory rock deformation experiments, the role of fractures and faults in exhumed mechanically multilayered rocks in order to better constrain the deformation mechanisms characterizing heterogeneous rocks. This study aims at evaluating 1) the fault zone evolution from incipient failure to mature faults, with increasing displacement up to tens of metres; 2) the role of the mechanical properties of multilayered rocks in fault initiation and evolution. Within mechanical multilayers, faults show staircase trajectory characterized by steeper portions in calcareous competent layers and flatter portions in incompetent marly layers. Mechanical data further provide an independent constrain for the high θ angles observed in the outcrop in correspondence of marly layers. With the progressive accumulation of displacement, this refracted trajectory tends to develop dilational jogs at first, then to straighten their trajectory and develop wider fault zones. Moreover, the overall asymmetry of the structure, due to the stress orientation, points out the important role played by the anisotropy in controlling fault geometry.
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Usinskoye Field (Timan-Pechora Province) - Lower Serpukhovian Oil Pools Sealing and Scattering
By E.B. RileThe lower Serpukhovian oil pools of Usinskoye field are exposed to various ways of sealing – by regional anhydrite top seal, by faults. They have also different ways of scattering – through the hydrodynamic window in the top seal, when the anhydrites are replaced with carbonates, or through the gap in the top seal caused by the faults. Faults role is ambiguous – in the case of Usinskoye field they are partly sealing at the anhydrite intervals, and they are not at the carbonate intervals. That is they are increasing or even form oil pools on the uplifted sides because thick anhydrites of the forth bed overlay porous carbonates of the third and destroying oil pools if they are located on the lowered side and come into contact with permeable rocks. In our particular case the faults in general play positive role. The correctness of the hypothesis is verified by correspondence between the discovered controlling object and the level of hydrocarbon-water contact.
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3D Fault Plane Geometry and Fault Scaling Studies Using Seismic Attributes
More LessWe have applied an advanced seismic fault attribute workflow to improve images of faults at different scales. The attribute volumes were used to study the actual geometry of fault plane in 3D in space. This fault plane assessment is independent of uncertainties imposed by traditional seismic-interpretation. We measured fault geometric attributes including fault length, displacement, and height from different seismic fault attributes to study fault-scaling properties. Our study showed that faults are segmented along their length and the number of segments increases towards the upper and lower tips. The distance between fault segments also increases towards the upper and lower tips. Fault length varies almost symmetrically through fault plane and reaches its maximum almost at the center of its extent. The displacement versus depth exhibits a narrow belly-shaped distribution. The depth at which the maximum accumulated displacement occurs does not coincide with the depth where the maximum fault length reaches.
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Characterization of Fault Zones for Reservoir Modeling - An Example from the Illizi Basin, Algeria
Authors L. Mattioni, B. Caradec, L. Jeannin and R.Y. CherifA fault seal analysis was performed in the south-eastern area of the Illizi Basin (Algeria) as an aid to improve reservoir management of this structurally complex region. The objective was to characterize the sealing mechanism, apply modern techniques to evaluate the dynamic behavior of faults in fault-seal analysis, and show how pressure data can be used for calibration with relatively limited subsurface data. The fault sealing analysis was conducted for each of the principal faults and reservoirs in the studied area. The analysis was based on detailed 3D seismic mapping at multiple stratigraphic levels. Intermediate horizons, including non-mapped sands and reservoir bases, were constructed based on the stratigraphy observed in well logs. Data from the already drilled exploration wells provided direct constraints on the stratigraphy in each fault block analyzed. The results of our study show the relevance of this kind of integrated analysis and give a more precise idea of the sealing capacity of faults in the study area of Illizi Basin of Algeria. The methodology could be confidently applied to other prospects/leads within the area to reduce the risk associated to the fault retention.
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Geological Condition and Characteristics for Formation of Deformation Bands - Example from Jizhong Depression, China
More LessDeformation bands mainly developed in high porous rocks whose porosity more than 14.3%. Deformation bands and fissure simultaneously developed in rocks with porosity between 10.1% and 14.3%. In high porous rocks, fault zone has bipartite texture. The fault core has cataclasite features. Deformation bands developed in damage zone. This thesis describes geological condition and characteristics of deformation bands according to well Jin 93-41X which was drilled across fault zone in Shulu Sag. The main controlling factors of the types of deformation bands are clay content and diagenetic stage. In pure sandstones, the grain flow is the deformation mechanism during unconsolidated to semi-consolidated of diagenetic stage, which formed disaggregation bands. Cataclastic bands developed during consolidation of diagenetic stage. In impure sandstones,the phyllosilicate bands formed during unconsolidated to semi-consolidated of diagenetic stage. The features of deformation bands are that the thickness of single deformation bands is several millimeters, and displacement is a few centimeters. They change the physical characteristics of parent rock obviously, and lead to the changes of porosity, permeability and displacement pressure. Cataclastic bands and phyliosilicate bands have the largest reduction in permeability. The changes of physical property promote the heterogeneity of reservoir, which has significant influence on fluid flow.
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Estimating the Coulomb Failure Function Using Seismic Velocities
Authors T. Colson, B. Boterhoven, D. Castillo and M. KeepFault seal capacity is an important component in the conventional petroleum system. Assessing the capacity for a fault to seal or leak can be difficult, particularly where well constraint is lacking. In the frontier basin, in a marine setting, the only data available may be from a seismic survey. However, useful constraints on a faults sealing capacity can be extracted from this data alone. This study investigates the robustness of a number of empirical relations that can assist in extracting useful constraints from seismic velocities. Reliable estimates on maximum and minimum stress tensors and pore pressures can be calculated and combined with basic fault architecture analysis, to aid in placing some practical constraints on fault risk. In this study an area on the Rankin Trend, North West Shelf Australia, found good correlation between well-based and seismic velocity-based pore pressures and stress magnitudes allowing a coulomb failure function based only on stacking velocities to be calculated.
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Characterization and Prediction of Seal Lithological Variability from Log and Seismic Data
By K.D. KurtevAuthor presents an approach for data integration at different scales and for characterisation and prediction of seal properties variations which define seal quality. Presented is an original methodology for seal mud-rich facies recognition from conventional logs and their distribution parameters assignment to the seismic attributes. Sensitivity analysis of the recognition and characterization methods is performed, which allows to quantify seal capacity and its determination uncertainty at seismic scale.
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Geometry, Microstructure and Petrophysical Properties of Compaction and Shear Bands at Silica Dome, Valley of Fire State
Authors A. Torabi, B.E. Jarstø, A. Cilona and S. DengWe characterized and compared shear and compaction bands formed in Aztec Sandstone in Silica Dome, Valley of Fire, Nevada, USA. We investigated various portions of a single sand dune (from bottom-sets to fore-sets), and documented multiple sets of compaction bands and shear bands. We have conducted geometric (length and thickness) and in-situ measurements of permeability and hardness of compaction and shear bands and the surrounding host rock. Microstructural analysis has been performed on thin sections of representative samples to understand and compare the characteristics of shear and compaction bands. Our results confirm that shear bands are longer and thinner than compaction bands in this locality. Density, elastic moduli and permeability of shear bands have a wider range than those of compaction bands. This reflects the heterogeneous microstructures, which relates to different degrees of compaction and cataclasis along the shear bands. Shear bands can reduce porosity and permeability more than compaction bands (in extreme cases), up to two orders of magnitude compared to host rock in this study.
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Growth Juxtaposition Diagrams - A New Angle on an Old Technique
Authors H. Anderson and C. Reilly1D juxtaposition triangles provide a quick way to evaluate across-fault horizon juxtaposition and sealing capacity in the absence of a 3D model. The diagrams are traditionally derived from a single well source and therefore do not incorporate across-fault horizon growth; an assumption which negatively impacts on the accuracy of the modelled juxtapositions. However,constraints on the extent of sedimentary growth is often readily available from secondary wells or adjacent seismic reflection data. Using this data two new types of juxtaposition triangle, “Two-Well” and "Percentage Growth”, can be constructed. Deriving growth data either from a secondary well or as a percentage increase in across-fault thickening, the new techniques are used to model juxtaposition and shale gouge ratio on a kilometre-scale growth fault in the Taranaki Basin, offshore New Zealand. The results indicate that Two-Well and Percentage Growth diagrams provide a more realistic representation of the fault sealing capacity than a 1D solution.
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Filling the Gaps – From Microscopic Pore Structures to Transport Properties in Shales
Authors T. Schäfer, R. Dohrmann, C. Greenwell and M. JensenThe presentation will be the summary of a workshop organized by the NEA Clay Club hold in conjunction with the EUROCLAY 2015 conference in Edinburgh focussing on new method development using electron, x-ray, neutron and laser- based analytical techniques used to characterize porosity, pore size distribution and pore connectivity in compacted clays and tight formations. This data will be discussed in light of molecular dynamic (MD) and 3D pore scale modelling approaches to explain anion and cation transport and mechanical behavior.
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Assessment of Fault-seal Integrity for Underground Storage of Natural Gas in Porous Sandstone
Authors L.D. Meng, X.F. Fu, X.L. Zhang, T.W. Li and J. LiuUnderground gas storage is widely employed for balancing the supply and demand of natural gas, mostly during cold winter periods. We investigate Banzhongbei gas storage (BGS) bounded by B816 and Banqiao fault in Dagang gas storage facilities acting as a swing-supplier to meet peak demand for Beijing, Tianjin and Hebei province. There was wasted natural gas exceeding 7.7×108m³in BGS from 2003 to 2013 that has been one of the most serious problems. There would be big risks on fault-seal integrity. Two aspects included fault membrane seal and fault stability are congsidered in the assessment of fault-seal integrity. We have calibrated the fault membrane seal capacity with the pressure differences across faults from three depressions in Bohai Gulf Basin. Based on that, we conclude that the B816 fault has low lateral capillary sealing capacity resulting in BGS and B814-B to be just one trap bounded by BQ fault. Lateral and vertival membrane seal assessment suggests BQ fault has higher capillary entry pressure (>4.5MPa) than that of stable fault chould sustain (3.0MPa). Hence, according to the stability of BQ fault that the risk of fault seal integrity focus on, modled maximal injection volumn is 13.7×108m3.
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Fault Seal Analysis of a Natural CO2 Reservoir
Authors J. Miocic, G. Johnson, S.M.V. Gilfillan, C.I. McDermott and R.S. HaszeldineFor potential CO2 storage sites it is crucial to know if faults will act as flow baffles or if CO2 will be able to migrate out of the reservoir complex. Geomechanical fault seal analysis for a CO2 reservoirs is very similar to hydrocarbon reservoirs. However, fault rock seals have the potential to act very different in a CO2-rock-water system compared to a hydrocarbon-rock-water system. Natural CO2 reservoirs are common in sedimentary basins world-wide and here we present the results of a fault seal analysis, with emphasis on juxtaposition and fault rock seals, of a natural CO2 reservoir from the Colorado Plateau. The reservoir has leaked CO2 for more than 350 ka along faults. Our results show that the existing gas column can overcome the capillary entry pressure of the fault rocks, leading to migration of CO2 to the surface. Additionally, the fault is orientated favourable for reactivation in the current stress field.
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Predicting Hydraulically Conductive Fractures - A Comparison of Methods
Authors S.A. Weihmann and D. HealyReliable estimation of fracture stability in the subsurface is crucial to the success of exploration and production in the petroleum industry, and wider applications in earthquake hazard, hydrogeology and waste disposal. Being able to predict the stability of fractures in a reservoir (or seal) can enhance recovery and returns. Previous work has suggested that fracture stability is related to fluid flow in rocks: specifically, that more highly stressed fractures tend to exhibit higher rates of fluid flow. Barton et al. (1995) and Ferrill et al. (1999) described positive correlations of fluid conductive properties and ‘active’ fractures in basement rock. This contribution tests the applicability and robustness of the published correlations of stressed fractures and elevated fluid flow by the methods of critically stressed fractures (CSF) and dilatation tendency (Td), by comparing observed intervals of elevated fluid flow to the predicted values of CSF and Td. In this preliminary scoping analysis, the fracture stability of 219 fractures are calculated from wellbore data. Results show that the relationship between active fractures and fluid flow is more complex than described by expressions such as CSF and Td.
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Geometry and Rock Properties Modelling of the Callovo-Oxfordian Claystone from a 3D High Resolution Seismic Cube
Authors B. Yven, M.G. Garcia and A.C. ChabironIn the context of a deep geological repository of high-level radioactive wastes, the French National Radioactive Waste Management Agency (Andra) has conducted, over the past 20 years, an extensive characterization of the Callovo-Oxfordian argillaceous rock in the Eastern Paris Basin. This research has served to demonstrate the feasibility and safety of deep disposal of high-level wastes and intermediate-level long-lived wastes. Today, this research is helping prepare for industrial disposal centre's construction and operation Therefore, the geometry and physical rock properties of the Callovo-Oxfordian claystone formation (COx formation) are required to position the repository, design its shape and numerically simulate its behaviour. This article details the sedimentological background and the results of the geological modelling of the COx formation in the contemplated repository area.
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Mechanical Anisotropy Characterization of the Draupne Formation, North Sea
Authors E. Skurtveit, J.C. Choi, M. Soldal, L. Grande, R. Maurer and P. HorsrudAnisotropy is an important characteristic for the mechanical characterization of shale. Both strength and elastic parameters vary with orientation of material due to the lithological anisotropy in the material. A triaxial test program on varying plug orientation was designed to investigate the mechanical anisotropy in the Draupne Formation. From the triaxial experiments, clear strength anisotropy is observed especially in certain range of orientation. Post-test CT images shows that the strength anisotropy is mainly related to failure in bedding planes. The observed strength anisotropy implies that orientation dependent failure criteria should be considered for realistic geomechanical modelling of seal integrity.
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Pressure-dependent Permeability of Shales
Authors E.H. Rutter, J. Mecklenburgh, R. McKernan and R. TaylorThe matrix permeability of shales is of great importance in determining the behaviour of shale seals and also of shale gas reservoirs. Methods of permeability determination must take into account sensitivity to variations in confining and pore pressures. We seek to establish whether common generic patterns of behaviour exist and to establish their parameters experimentally. Pressure sensitivities of two shales are compared, but the same pattern also applies to others. They follow the general law k = A exp(- g(Pc – a Pp)) (1 + D/ Pp) in which k is permeability, Pc is confining pressure, Pp is pore pressure, A, g, a and D are empirical parameters. g and a describe the sensitivity to confining pressure and pore pressure and variations of k by more than 3 orders of magnitude can occur over the whole reservoir pressure range. Slip (Klinkenberg) flow begins to be significant at gas pore pressures below about 50 bars. Partial fluid saturation leads to a reduction in permeability, and in all cases flow is highly anisotropic. If pressure sensitivity of permeability is not taken into account, reservoir evaluations from well tests will lead to substantial overestimation of original gas in place and likely yield with time.
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Past and Present Permeability, Fluid Flow and Self Sealing in a Marl-limestone Sequence in Northern Switzerland
Authors M. Mazurek, G. Deplazes, P. Marschall and D. TraberThe Effingen Member in northern Switzerland, a potential host formation for the disposal of radioactive waste, has been studied in boreholes and outcrops, with the objective to describe its hydraulic, geochemical and fluid-flow characteristics. The hydraulic conductivity within the sequence of Oxfordian marls and limestones is generally very low, with the exception of a fractured limestone sequence that constitutes a potential lateral flow path. Calcite-celestite veins occur frequently and, in most cases, efficiently seal pre-existing fractures. Geochemical data, in particular 87Sr/86Sr ratios and δ18O values of carbonate, yield contrasting characteristics in veins and rock-matrix carbonate, leading to the conclusion that the veins are externally sourced and document open-system behaviour. Given the fact that even the micrite of the rock matrix was partially recrystallised during this stage fluid infiltration, it is concluded that at some time in the past the formation had a substantially higher permeability than today over an extended period of time and that since then, vein formation, in addition to clay swelling, resulted in an efficient self sealing of the formation, except in the most carbonate-rich beds.
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Experimental Observations of the Flow of Water and Gas along Fractures in Shales and Clay Gouge
Authors R.J. Cuss, J.F. Harrington, C.C. Graham and A.C. GrahamA series of laboratory experiments has been undertaken to determine the flow characteristics in Opalinus clay (OPA) and Callovo-Oxfordian claystone (COx). The flow characteristics are far from simple. For example, in OPA, initial swelling of the fractures reduced fracture flow by one order of magnitude. Shear reduced flow by a further order of magnitude and is an effective self-sealing mechanism. However, continued shear increased flow by over four orders of magnitude possibly due to the formation of new microfractures or due to the interaction of fracture asperities and the opening of conductive channels. The injection of gas had no detrimental effect on the hydraulic properties of the fracture. The gas entry pressure of OPA appeared to remain unchanged by shearing and this suggests shear was not an effective mechanism to reduce fracture gas transmissivity. COx showed considerable hysteresis during an unloading cycle demonstrating that stress history is an important aspect of predicting the flow of discontinuities; whereby flow is more closely related to the maximum stress experienced, as opposed to the current stress regime.
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Fault Seal Analysis Incorporating Shale Smear - Implications for Upscaling
By N.T. GrantA simple 1D model has been built to include shale smear in quantitative fault seal prediction. The model uses well data in much the same way as the familiar triangle diagram. Instead of presenting the results as complex juxtaposition diagrams however, the model uses graphical outputs that focus only on windows in the predicted shale smear envelope. Individual smears are calculated using the shale Smear factor (SSF). The smear envelope is generated by mapping each potential smear onto the fault plane using a probabilistic approach, tied to a range of different shale smear geometries. The results show that the across-fault connectivity is affected by the smear placement model used together with the critical SSF for smear discontinuity. The 1D model also allows the impact of geocellular up-scaling to be assessed. First a high-fidelity layer model is built using the well data. This is then up-scaled to create a blocked model, which is then resampled to derive the equivalent “upscaled” layering. Layer thickness (rather than cell dimension) is an implicit requirement for smear prediction using the Shale Smear Factor (SSF). The 1D model is able to assess the impact of varying geocell dimensions on the fault seal prediction. Whether a fault becomes more or less sealing due to upscaling is a function of the net/gross and stacking pattern of the reservoir and seal layers.
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Permeability Anisotropy in Faulted Sandstone - Implications for Fault Seal
Authors N. Farrell and D. HealyQuantifying the permeability of fault zones and fault rocks is critical to the success of exploration and production. Directional variations in permeability have previously been reported from clay-rich fault rocks, but here we describe significant permeability anisotropy in fault rocks produced from two different sandstones, an arenite and a sub-arkose. In both cases, the maximum permeability of the fault rock is aligned with the fault slip vector in these normal faults, and the minimum permeability is oriented in the fault normal direction. Permeability anisotropy spans 3-5 orders of magnitude in both cases, and has major implications for the prediction of sealing behaviour in the subsurface. While the across fault permeability in our samples is low and the faults might be predicted as sealing, the along fault (up-dip) permeability is so high that leakage along the fault is a real possibility. Our results highlight the need for careful analysis of directional variations in permeability, especially in fault zones and fault rocks.
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Tectonic Control on Cataclastic Strain Distribution and Permeability Reduction in Porous Sandstone Reservoirs
Authors G. Ballas, R. Soliva, H. Fossen and R.A. SchultzWe combine a thorough structural and petrophysical analysis of multiple deformation band sets (France, USA, Germany, Taïwan, Uk) with a broad dataset synthesis of deformation band permeability from the literature. Our analysis first reveals that strain localization in porous sandstones is characterized by fault zones surrounded by sets of shear bands showing a high degree of comminution. In contrast, distributed strain, does so in the form of pervasive and closely spaced compactional shear band and shear-enhanced compaction-band sets, showing moderate and low degree of comminution, respectively. Shear strain localization is inherent to the normal fault Andersonian regime and locations of upward-propagating underlying faults. In contrast, compactional strain distribution is inherent to thrust fault Andersonian regime. A synthesis of band permeability data reveals strong permeability decrease with the increase of comminution, especially in the normal fault regime. This demonstrates a major control of tectonic setting (extension/contraction) on fluid transmissibility of porous sandstones reservoirs containing cataclastic band networks. These results are consistent with a mechanical model proposed earlier based on the analysis of porous granular materials subjected to burial, different stress conditions and material properties.
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The Rôle of Faults on Hydrothermal Circulations in the Têt Valley (Eastern Pyrénées)
Authors A. Taillefer, G. Martin and R. SolivaHot springs in continental systems often localize near major faults. Faults may act as drains or barrier for hydrothermal circulation, depending on their core zone constitution and permeability, and the fracture density, opening, and connectivity in their damage zone. The interplay between these processes is still unknown and remains to be studied. The french eastern Pyrénées hot springs are an ideal case to understand how faults controls hydrothermal circulations and hot springs distributions. They align with the brittle normal Têt fault. The basement rocks affected are composed of highly fractured, foliated, gneisses, granites, and metasediments. Photo-interpretation and field work reveal that hot springs discharge in the footwall, along a ductile fault (CMNC), or at the Têt fault linkages with subsidiary brittle faults. Because of the topographic gradient induced by the fault offset, fractures and foliation drive meteoric water toward the deep reservoir where it acquires temperature. Hot waters then use damage zone fracture to rise up, restricted in the footwall because of the presence of main drains in the damage zone and poorly permeable fault rocks in the core zone. Well oriented in-situ stress or seismic activity, could help to maintain the fractures opening, which are generally cemented by zeolites.
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Flow Around Fault zones in Siliciclastic Reservoirs Based on Limited Available Data During Hydrocarbon Exploration
Authors J.H. ter Heege and G. De BruinThe sealing capacity of faults is one of the main controlling factors determining column heights of hydrocarbons in structural traps and potentially bypassed gas in undrained reservoir compartments. Limited available data in early exploration phases often hampers full incorporation of fault seal analysis and fault zone permeability in exploration efforts. In this study, an analytical model has been derived that constrains flow around fault zones in siliclastic reservoirs, including effects of non-isotropic permeability in fault core, damage zone and intact reservoir. It is shown how limited site-specific data can be combined with data from literature to constrain the model parameters. Once model parameters are constrained for a specific compartmentalized reservoir, the model can be used to determine the interplay between matrix, damage zone and fault core permeability in determining flow around fault zones and optimize well planning.
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Dynamic Modelling of Faults for CO2 Storage - Insights from the CO2CRC Otway Project
Authors E. Tenthorey, T. Dance, J. Ennis-King, Y. Cinar and J. StrandIn this paper, we present the methodology and results of the various fault modelling that was conducted so that the project could confidently proceed from the safety and integrity perspective. The work is broadly divided into two components. The first component is to assess the likely pressures generated by CO2 injection and to assess whether or not the faults would remain stable under such perturbations. The second component of the work assesses both the across-fault and up-fault hydraulic properties of the fault that is proximal to the injection well. Subsequently, the fault parameters are incorporated into dynamic simulations to determine how far vertically up the fault CO2 is likely to migrate. The incorporation of fault properties into commercially available simulator is not a straight forward workflow, and we will discuss approaches that can be taken in this regard.
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Widening of Normal Fault Zones During Vertical Propagation
Authors V. Roche, C. Homberg, M. van der Baan and M. RocherIn this paper, we document the early stage of faulting, based on detailed observations on mesocale faults in layered rocks. The vertical propagation of the studied faults is stopped by layer-parallel faults. This restriction involves a modification of the fault structures: far from the restricted tip, fault structures correspond to a simple planar slip surface, near the restricted tips, their structures range from a planar structure to a complex fault zone characterized by abundant parallel fault segments. Based on the observations, we developed a model of fault zone evolution in which fault zone complexity, specifically the number of sub parallel segments, increases to accommodate increasing strain, during restriction. Eventually, the fault should finally propagate beyond the layer-parallel faults with a complex geometry inherited from the period of restriction. This model implies that fault widening is controlled by the host rock and formerly developed fractures. Wide fault zones are expected in layered rocks with strong mechanical heterogeneities and with preexisting joints and layer-parallel faults. Likewise, fault growth occurs with non-linear increasing in maximum displacement, length, and thickness, due to restriction. Such a model of fault impacts on the vertical permeability and the seismic behavior of the rock.
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Importance of Decompaction and Restoration for Temporal Fault Displacement and Fault Seal Analysis
Authors C. Reilly and H. AndersonTemporal fault analysis can give previously unexplored insights into the sealing and leaking capacity of faults over geological time and offer robust estimations of the timing and kinematics of fault histories. A fundamental aspect of temporal fault analysis, particularly quantitative fault seal studies, involves the sequential incorporation of decompaction and valid structural restoration to produce accurate representations of fault and horizon palaeo-geometries. This study uses Midland Valley’s Move™ software to detail the differences seen in fault displacements analyses when compaction is taken into account. Real and synthetic models have been used to highlight the importance of decompaction in displacement and seal analyses. Magnitudes of displacement are shown to be underestimated by up to several hundred metres when decompaction is not carried out and periods of reactivation on a fault can be obscured. Furthermore, estimation of temporal shale gouge ratios and palaeo-juxtapositions are likely to be more realistic with the use of sequential restoration, accounting for sediment compaction. We propose a sequential restoration and decompaction methodology as a fundamental part of any temporal fault displacement and fault seal analysis.
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Structural Architecture and Paleofluid Evolution of Strike-slip and Normal Fault Zones, Jabal Qusaybah Anticline, Oman
Authors L. Clemenzi, F. Balsamo, F. Storti, M. Mozafari, J.G. Solum, R. Swennen, C. Taberner and C. TueckmantelThe E-W-trending Jabal Qusaybah anticline is located at the western termination of the Salakh Arc, Oman Mountains. Jabal Qusaybah exposes the Cretaceous Natih carbonates, folded in a ~10 km long anticline characterized by a complex fault pattern which mainly includes (i) NE-SW left-lateral strike-slip and (ii) N-S extensional fault zones. The N-S striking extensional fault zones are perpendicular to the fold axis and best developed in the central sector of the anticlinal crest. They are geometrically confined within major NE-SW left-lateral strike-slip fault zones, forming an overall transtensional horsetail array. Collectively, our findings show that, in this transtensional setting, the fault zones acted as preferential pathways for fluid flow during folding, and that the central part of the anticline is the more dilatant sector. Furthermore, damage zone H/S ratio versus displacement diagram indicates that the structural position, rather than fault throw, is the parameter controlling the location of the more dilatants fault segments.
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Investigating Fault Zone Development, Geometries and Properties in Mixed Carbonate and Clastic Successions
Authors T.J. Cain, S.M. Clarke and A.G. LeslieFaults and associated fault zones are key controls on many processes within the brittle upper crust; their individual properties are a controlling factor on the mechanical and fluid transport properties of their protoliths. Despite an impressive volume of work ranging from classic concepts to recent key advances, many features of fault structure and along-strike fault heterogeneity are poorly constrained. This knowledge gap can partially be attributed to outcrop studies that are hindered by a lack of continuous, truly three-dimensional exposures. This work aims to address this paucity in data and presents the preliminary results from an unparalleled dataset comprising LiDAR, photogrammetrically-derived point clouds, wireline geophysics, coal-seam survey data and field observations of fault, and fault-zone architectures. We aim to present preliminary results from a study of fault, and fault zone architecture within mixed siliciclastic and carbonate rocks contained within the Midland Valley basin, Scotland, UK. Three-dimensional fault architecture models have been created using LiDAR, photogrammetrically-derived point clouds and surveyed coal data interpreted in a three-dimensional virtual environment. Models are augmented with measured fault core geotechnical data in order to accurately numerically simulate fluid flow.
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Static and Dynamic Fault Seal Potential in Carbonates
By J.G. SolumConstraining the seal potential of faults in carbonates will undoubtedly be more complicated than with faulted clastics due to the greater chemical reactivity of carbonates, and will require integration of geochemistry/diagenesis and structural geology. Nevertheless, rules to predict fault seal potential in carbonates must be developed since the lack of an ability to quantitatively risk carbonate fault seal hinders estimates of in place hydrocarbon volumes (is an unpenetrated fault block likely to be filled?) and well development plans (what values of fault transmissibility or permeability anisotropy can be expected; how many wells will be required?. The need to develop the ability to characterize seal potential of faults in carbonates in the near future is highlighted by three observations: 1) Carbonate reservoirs that are defined at least part by faults are common and have a global distribution; 2) There is a growing number of carbonate-carbonate juxtapositions that appear to be sealing over geologic and/or production time scales; 3) There are a number of processes by which faults in carbonates can develop seal potential.
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Frictional and Hydraulic Behaviour of Carbonate Fault Gouge During Fault Reactivation - An Experimental Study
Authors C. Delle Piane, A. Giwelli, B. Clennell and J. RaimonWe presents results from an experimental program designed to shed light on the effect of stress and deformation history on the permeability and slip behaviour of faults in carbonate rocks. We investigate the mechanical and hydraulic behaviour of experimentally created fault cores and damage zones in natural travertine rock samples and also explore the role of a sealing layer on the frictional and hydraulic response of the rock. Following direct shear testing on the blocks, cylindrical plugs with diameter of 38mm were drilled across the slip surface to be tested in a conventional triaxial configuration monitoring the permeability and frictional behaviour of the samples. The results indicate that the fault cross cutting the sample is acting as seal and its permeability is negatively affected by an increase in mean effective stress; slip on the fault plane does not improve the permeability of the fault. It can be therefore concluded that leakage along an un-cemented carbonate gouge cannot be achieved by movement on the fault plane alone, at least not within the range of slip measureable with our apparatus (; other mechanisms (e.g. cementation of the gouge) need to be explored to assess the possible leaking scenarios in faulted carbonate rocks.
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Using Field and Lab Data to Improve the Simulation of Faulted Carbonate Reservoirs
Authors E.A.H. Michie, G. Yielding and Q.J. FisherAlthough the ability to predict the sealing potential and transmissibility of carbonate-hosted fault zones has received significant interest, there is surprisingly little published data on the petrophysical properties of variable fault rock types within carbonate reservoirs. Intact and deformed carbonates have a high heterogeneity and propensity to react with fluids; however patterns to this heterogeneity can be observed and used as predictive tools when considering fluid flow across carbonate fault zones. Several carbonate-hosted fault zones have been examined to determine the type and distribution of fault rocks and their influence on fluid flow. Analysis of these fault zones has revealed that fault rock type, and corresponding porosity and permeability, is mainly controlled by lithofacies variation, lithofacies juxtaposition and displacement. Varying textures in different lithofacies control whether the strain is localised, causing grain crushing, or dispersed creating fractures that can hydraulically brecciate to produce a variety of breccia types. Each fault rock type has different porosity and permeability values, creating a large range to both porosity (1.6-34.7%) and permeability (0.0001-1000 mD). However, trends to these petrophysical properties are observed, depending on the three main controlling factors stated above, and can be used to predict a fault's transmissibility.
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