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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 - 20 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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