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2nd EAGE International Conference on Fault and Top Seals - From Pore to Basin Scale 2009
- Conference date: 21 Sep 2009 - 24 Sep 2009
- Location: Montpellier, France
- ISBN: 978-90-73781-69-6
- Published: 21 September 2009
61 - 78 of 78 results
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Sub Log-scale Heterogeneity of Fine-grained Sediments – Implications for Effective Permeability and Top Seal Risking
Authors M. Drews, K.D. Kurtev, J. Ma and A.C. AplinEffective permeability plays an important role in prediction of leakage rates, seal capacity and quality. Current best practice uses conventional log data (15 cm as maximum resolution) to assess effective flow properties in seal sections and, with a maximum resolution of 15 cm, miss out the cm-scale sedimentological variability which is quite common in some mud-rich settings. The aim of this study was to identify and classify a reasonable number of different sedimentological heterogeneities and to investigate their impact on flow properties based on high-resolution data (microresistivity and core images). Four types of fine-grained sediments were defined on a basis of lithological variability and internal structure. Methods from geostatistics, such as the variogram as a descriptor for sedimentary structures derived from microresistivity and core images, were employed to quantify differences on a cm-scale between the four fine-grained sediment types. Furthermore, 2D flow models on a meter scale based on microresistivity and core images were used to determine ranges of effective permeabilities for the different types of fine-grained sediments. Finally, these effective permeabilities were upscaled in 1D and used to compare the differences due to the sampling rate of conventional and high resolution measurements.
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Risking Vertical Fault and Top Seal Using Gas Chimneys
More LessGas chimneys and related hydrocarbon migration pathways have been highlighted in seismic data using a supervised neural network, to visualize them in 3D and map their morphology. Using this information on over 125 fields and dry holes (containing effective reservoir)traps were divided into top seal and fault traps.Fault traps have been divided into three classes. Fault Flank Trap where the fault is involved in charging the trap from the flank are low risk high integrity traps. Fault Seal Traps show clear evidence of chimneys related to deep seated faults which terminate at the reservoir interval. They are high integrity traps. Fault Leak Traps have fault related chimneys observed at the crest of the structure. They are moderate to low integrity traps (LIT-MIT), and represent higher risk for vertical seal integrity. Top seal traps have been divided into four classes based on the nomenclature of Cartwright et. al. Gas Cloud Traps are low risk, but moderate integrity traps. Seepage Pipe Traps, Blowout Pipe Traps, and Mud Volcano Traps have increasing risk of seal failure, but can hold economic quantities of hydrocarbons, if buried or being recharged.
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Relationship Between Pore-scale Characteristics and Petrophysical Properties
Authors Z. Jiang, K. Wu, G.D. Couples, A. Ryazanov, M.I.J. van Dijke and K.S. SorbieFluid flow properties of geomaterials are fundamentally controlled by the characteristics of the pore system and the interaction of different fluid phases occupying complex pore shapes. Both the geometric and topological characteristics of the pore system are important, and each separately influences the flow of fluids. Here, we report a study in which we use network models to assess fluid flow through pore systems extracted from coarse-grained and fine-grained materials. Arbitrary changes to the pore systems, which mimic the effects of compaction, diagenesis, and possibly deformation, produce changes in the multi-phase flow properties, but the roles of pore size and connectivity vary in different materials. Continuing studies aim to identify predictive relationships between readily-obtainable descriptors and the hard-to-determine flow characteristics.
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Seals, Superseals and Faults
Authors J.W. Wheeler and K.E. WilliamsSuperseals are qualitatively different from conventional hydrocarbon seals because they confine water and abnormal pressure, not merely fluids that are immiscible with water. In the normal course of dewatering, common shales are largely invisible to expelled water. In some basins, sediment can accumulate so fast that thick common shales can interfere with dewatering sufficiently to cause transient overpressure. Superseals, such as the Woodford Shale, are impermeable to water and can retain overpressure indefinitely. The identification of superseals may have an impact on both the sequestration of carbon dioxide and the isolation of certain waste materials. Common shales are able to trap hydrocarbons because the pore entry pressures for fluids other than water are very high (a capillary seal), but the shale remains transmissive to water and to some solutes. A common shale seal is unsuitable as a barrier to carbon dioxide. A shale superseal will retain CO2. Horizontal pressure compartments are also very common and must also be accounted for in basin models. The sealing capacity of a fault is determined by the capillary entry pressure of the sealing rock unit (or fault gouge zone). The sealing capacity is increased where there is a pressure differential across the fault.
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Using 3D Geomechanical Modelling To Evaluate Stress-related Fault Seal Risk – A Timor Sea Case Study
Authors L. Langhi, Y. Zhang, A. Gartrell, J. Underschultz and D. DewhurstObservations from the Timor Sea suggest that the high incidence of breached Jurassic traps is a result of recent fault reactivation. Based on comparison between structural evolution and charge history, it has been proposed that the variation in strain accommodation between faults was critical in determining up-fault flow patterns. A geomechanical 3D model is used to simulate the response of trap-bounding faults to extensional reactivation. The model makes predictions on stresses/strains and fluid flow partitioning and is used to characterise the interaction between the deformation state and fault seal efficiency over an area including the Laminaria and Corallina oil fields. When integrated with well data and evidences of fluid remigration, the model results show their ability to constrain trap integrity predictions and isolate leaking/sealing fault segments. The model captures the inhomogeneous distribution of sealing fault segments driven by strain partitioning and structural architecture. It emphasises that fault tip interaction, fault growth process and fault plans arrangement all play a major role in controlling fault seal evolution.
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Fault Core Composition and Thickness-displacement Relationships of Extensional Faults in Fine Grained Carbonates
Authors E. Bastesen and A. BraathenConventional fault seal methods derive transmissibility properties of faults by calculating the shale gouge ratio along the fault. Fault thickness is a key parameter. However, the method does not consider intrinsic fault complexities, such as lenses, varying fault rocks and diagenetic elements. In this study we present a characterization of fault cores in carbonates, based on an analysis of fault composition with respect to the displacement/thickness relationship (D/T). Using a Fault Facies type description of rocks we have compiled and analysed the dimensions and composition of 100 faults cores from Sinai, Oman and Svalbard. These areas display thick succession of sedimentary carbonates truncated by extensional faults. Common volumetric elements of the cores (core facies) include fault rocks such as breccias, calcareous gouge and shale gouge (smear) and layers of calcite precipitated on the walls of slip-surfaces. The overall increase in thickness relative to displacement, showing a lower increase of fault thickness for large scale faults than for small scale faults, fits a power law distribution with an exponent lower than one. The individual fault core facies display different D/T than the overall D/T relationship, indicating that protolith, diagenetic effects and tectonic environment influence the observed thickness increase.
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Pedogenetic Effects in Fault Evolution
Authors I. Cantarero, A. Travé and G. AlíasDuring the late Oligocene – middle Miocene, an extensive deformation took place in the Western Mediterranean. In this process, main faults of NE-SW striking direction bordering horsts and grabens of the Catalan margin and minor faults perpendicular to the former were formed. We have studied some of these minor faults affecting Miocene conglomerates in the Barcelona Plain. The fault zone is formed by an absent damage zone and a poorly developed fault core. Their fault rocks are obliterated by later pedogenetic processes that have changed fault and fault rock properties and consequently fault rock classification. Nowadays fault rock is a cataclasite but because it is cemented by later pedogenetic processes, in fact, in origin was a gouge. When fault rock was a gouge (stage 1), and considering fault zone architecture, cross-fault flow could exist. During the second stage, after fault rock pedogenesi, new minerals reduced effective porosity and so permeability of the fault rock. The consequence was the seal of faults and compartmentalisation of flow. In conclusion, faults occurring in the upper meteoric environment can have other kind of processes responsible of their impermeabilization than deeper faults.
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Fault-zone Localisation in High-porosity Sandstone Reservoirs and Impact on Flow Efficiency
Authors C.A.J. Wibberley and E. SailletWe present results from a study of the distribution of deformation bands and larger ultracataclastic faults in a high-porosity sandstone reservoir outcrop analogue. We show that tectonic loading path and the nature of the stress changes causing deformation may strongly influence strain distribution. Localisation of deformation onto a smaller number of larger ultracataclastic fault zones is more likely in an extensional context than a compressional one because of the work-hardening nature of deformation band formation: In the extensional context, the differential stress required to continue deforming deformation bands is much less than in the compressional case, and may be achieved by subtle differences in stress variation around faults or small fluid pressure changes. Using new permeability measurements of host rock and deformation structures, we test models for the impact of these structures on flow rates in a producing field. Calculations of flow efficiency show that a small number of larger ultracataclastic faults may severely impede flow during production. Low-displacement deformation bands, with a much less reduced permeability however, will have a much lower impact on flow rates despite their higher densities. The impact of small deformation bands is likely to be greatest when produced by tectonic shortening.
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Stochastic Modeling of Permeability Reduction and Enhancement in Faults and Damage Zones
Authors T. Murray, G. Christie, J.P. Brown and S. TysonDuring appraisal, development and production of oil and gas fields a large amount of effort is applied to understanding the impact of changes in permeability around faults. In this paper we describe a methodology for calculating distributions of static permeability in and around faults incorporating, geomechanics.
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The Whitehouse Shore – A Natural Laboratory for Characterizing Fault Geometry, Heterogeneity and Permeability
Authors Y. Kremer, Z.K. Shipton, R.J. Lunn, C.A.J. Wibberley and J.K. InghamThe Whitehouse shore intertidal exposure (Scotland) provides an excellent field site to study small scale faults in sand-shale sequences. Especially interesting is the presence of paleo fluid flow indicators, which allow us to constrain the fluid flow behaviour of the faults and fractures at depth. Combination of field study, laboratory analysis and numerical modelling allows us to collect vast amounts of data on the geometry, heterogeneity and permeability structure of fault zones. These data will ultimately form the basis of a new workflow that allows the spatial variability of fault zones to be represented in reservoir models.
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Multi-episodic Fault Movements and Karstic Fills Along the Vallès-Penedès Fault, Coastal Catalan Ranges, NE Spain
Authors V. Baqués, A. Travé, A. Benedicto and P. LabaumeWe describe different fault rocks within a normal fault bordering the Neogene Vallès-Penedès basin in NE Spain. Through this fault, the Lower Cretaceous limestones of the footwall are in contact with the Miocene siliciclastic sediments of the hangingwall. In the Lower Cretaceous protolith, cataclasites and breccias are a mixture of tectonic and karstic products resulting from multi-stages movement and development of the fault. The localisation of frictional processes generated a cohesive fault breccia and the cataclasite during the progressive opening of the hydrological system. Later, when the fault reached the surface, meteoric diagenetic processes leaded to the formation of calcretes and karstic features and generating the breccia with the pisolithic matrix.
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Geomechanically-derived Fault Zone Petrophysical Properties – A Synthetic Fault Model Study
Authors A. Paez, H. Lewis, G.D. Couples and J. MaA 2D geomechanical model of a fault zone has been used to develop porosity and permeability distributions that reflect the geomechanical rock damage. A pseudo-3D geomodel, where fault displacment varies from zero to maximum has been created and a method developed to appropriately populate it with porosity and permeability values. Both dilational and compactional deformation occurs in this normal fault,as is expected in real subsurface faults, resulting in both increased and decreased (relative to the matrix) permeability values. Geometrically equivalent geomodels using a range of transmissibility multiplier to represent the fault have also been generated. These six geomodels (5 with transmissibity multipliers and 1 with geomechanically-derived poroperm) have then been converted into an industry-standard flow simulation that vary only in the treatment of petrophysical properties around the fault zone. The resulting flow simulations show that the geomechanically-controlled poroperm properties to a better job of representing the kind of complexity of e.g. across-fault pressure regimes and fluid saturations that are encountered in subsurface reservoirs.
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Fault Sealing Behaviour of Soft-sediment Extensional Faults in High-porosity Sediments from the Crotone Basin, Italy
Authors F. Balsamo and F. StortiThe hydraulic behaviour of deformation band-dominated fault zones is strongly controlled by the petrophysical properties of the protolith sediments, deformation intensity and environmental conditions of deformation. To provide further constrains on the relationships between fault structure, displacement and hydrology, we acquired structural, granulometric and permeability data from a total of 25 extensional fault zones developed in high-porosity sandy sediments of the Crotone basin, having mean permeability values in the 10E3 to 10E5 mD range. Fault core rocks developed by progressive grain size reduction and consist of foliated granular material and gouge lenses along striated slip surfaces. Mean fault core rock permeability ranges between 10E1 and 10E4 mD, although we recorded permeability values lower than 10 mD. Fault damage zones consist of closely spaced cataclastic deformation bands with different degree of complexity and mean permeability between 10E2 and 10E4 mD. By combining structural and hydraulic information, we obtained empirical quantitative relationships between bulk permeability variations, fault zone thickness variations, and fault displacement. Most of permeability reductions in both fault cores and damage zones occur at sub-seismic scale, whereas such a rapid permeability decay significantly decreases for displacement greater than 25-30 m.
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Quadshear – A New Kinematic Model for Clay Smear Development
Authors M. Welch, R.J. Knipe, C. Souque and R.K. DaviesA new kinematic model, based on the Trishear model, has been developed to simulate fault-propagation folding in ductile, clay-rich strata between two propagating faults, a process which often leads to the development of clay smears which can cause the fault to seal. The new model is used to determine the amount fault throw required for the continuous clay smears to break down, normalised to the bed thickness (this ratio is often known as the critical clay smear factor or CCSF). We find that the maximum length of continuous clay smear is primarily dependent on the position of the clay-rich bed in the stratigraphy, and the rate of propagation of the faults. The thickness of the clay-rich bed, the horizontal offset of the two propagating faults and the width of the fault-propagation folds have much less impact on the maximum length of continuous clay smear.
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The Development of Sub-seismic Fractures around a Fault – The Causes and the Implications for Fluid Flow
Authors D.C. Tanner and C.M. KrawczykThree parameters control the development of secondary sub-seismic fractures: Material properties, the fault displacement and its morphology. We demonstrate how restoring seismic faults with three dimensional geometrical kinematic modelling can generate information about the intensity and orientation of the fractures around the fault.
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Fault Compartmentalization of a HP/HT Field
Authors S. Hoth, S. Ottesen and T. OdinsenFault compartmentalisation maps have been produced for two reservoir horizons for a field located on one of the deepest fault blocks in the Viking Graben. Mapped fault rock properties in conjunction with Mercury injection data were used to calculate maximum Hydrocarbon columns and associated threshold pressures to obtain a static fault seal model. In general mapped fault rock properties indicate a high lateral and vertical variability. Key uncertainties comprise the structural interpretation and the relation between Mercury injection pressure and SGR. Given the presence of different Hydrocarbons, interfacial tension is expected to vary within the field significantly, thus giving rise to different column heights and threshold pressures for the same fault rock type. Thus, the structural compartmentalisation is superimposed by an HC property compartmentalisation and their spatial distribution is not expected to be the same. Given the HP/HT nature of the field, even low SGR fault rocks can sustain several 10's of meters of HC columns. The compartmentalisation maps in conjunction with the present Gas Water Contacts, the Gas Oil Ratio distribution, as well as the resulting communication paths, provide strong support for an upside potential for some compartments surrounding the discovery wells.
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Optimizing Fluid-rock Properties in Compartmentalized Reservoirs By Using Dynamic and 4D Seismic Data
Authors R. Villegas and Q. FisherIn this work we develop improved constraints on fault areas and define methods for history matching using both production and 4D seismic constraints, which will provide a more robust basis for production forecasting. We propose improved workflows to change the fault areas into the simulation model specifically by modifying the relative permeability near the faults and by considering two phase flow together with the 4D seismic data results.
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Integrated Hydrodynamic Analysis of Fluid Pressure and Leak-off Pressure Distributions to Evaluate Seal Effectiveness
By J.M. VerweijHydrodynamic methods are used to analyse the present-day fluid overpressure and leak-off pressure distributions in offshore Netherlands in combination with recently completed stratigraphic and structural maps, and knowledge on distribution and characteristics of oil and gas accumulations. This paper presents an overview of the results, including an improved characterisation of the permeability framework of offshore Netherlands with focus on the seal effectiveness of the low permeable units and identification of locations of seal breach risk.
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