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Fifth International Conference on Fault and Top Seals
- Conference date: September 8-12, 2019
- Location: Palermo, Italy
- Published: 08 September 2019
41 - 60 of 76 results
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Influence of Host Rock Lithology Contrast on Permeability Reduction in Fault Zones (Vienna Basin, Austria)
Authors T. Schröckenfuchs, V. Schuller and A. ZamolyiSummaryIn order to calibrate fault seal capacities to a specific basin, faults were analysed using core material. This calibration was conducted on several Neogene hydrocarbon fields in the Vienna Basin, Austria. Laboratory results showed a significant permeability reduction in all fault rocks compared to the host rocks. The highest and lowest sealing capacities were observed in rocks classifying as cataclastic bands. Although these cataclastic bands showed a broad variation in sealing capacity, the reason for the strong variation could neither be related to the depth at time of faulting or secondary cementation nor the shale/phyllosilicate content or the maximum burial depth of the host rock. Therefore all samples underwent further microscopic investigation. The examined samples revealed that the sealing potential of the fault rocks is strongly linked to the detrital carbonate content in the host rock. Our study shows that addressing the lithology variations in the host rock should not be neglected for fault seal analysis.
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Laboratory Investigations of the Properties of Volcanic Ash Seals
Authors T. Vanorio, J. MacFarlane and A. ClarkSummaryAn essential part of understanding seals includes studying the physical and mechanical behaviors of seals upon chemical interaction with fluids in the subsurface and, specifically, how chemical cementation and fluids being potentially aggressive impact the mechanical behavior of the bonded fabric. In this paper we focus on the chemistry of the cementation process of volcanic ash, the resulting formation of fibrous minerals and their impact on strength, and the role of CO2 in undermining such a cementation process. Intriguingly, volcanic ash and many of the fluids present in the subsurface (i.e., lime, alkalis, and sulfur) have been used to produce ancient mortars and still used in modern cementitious binders. This intertwining of the cementation of ash-based mortars and ash beds in the subsurface is an opportunity for cross-fertilizing knowledge across the Geosciences and Engineering, which is crucial to understand how fluid chemistry controls or undermines the cementation and strength of seals in the subsurface.
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Visualising Hydraulic Fractures in Bedded and Fractured Shales: A Series of Analogue Experiments
Authors A. Wiseall, R. Cuss and E. HoughSummaryThe rapidly growing shale gas industry, especially in the United States, has led to a growing number of research questions associated with understanding the controls on hydraulic fracturing. Having a better understanding of these controls will lead to an improved industry for both regulators and industry. Classic fracture mechanics states that hydraulic fractures will propagate in the direction of the maximum stress, which at these depths is often vertical. However, micro-seismic data from the industry shows that hydraulic fractures often have a considerable lateral extent. The natural heterogeneity of shales and there often heavily fractured nature has been hypothesised to explain this. To test this hypothesis a series of analogous hydraulic fracture visualisation experiments have been carried out using high speed photography of up to 1000 frames per second. Both layered arrangements of Bowland Shale and kaolinite clay discs and fractured arrangements have been examined. Hydraulic fractures were shown to become lithologically bound dependent on material properties. Furthermore, complex interactions between hydraulic fractures and natural fractures was observed. Further work is required to understand the way material properties govern fracture propagation. Results from this can be combined with well characterised shale formations to produce more accurate hydraulic fracture propagation models.
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Textural Controls on the Permeability and Structure of Fault Zones in Shallow Burial Limestones, Malta
Authors A. Cooke, Q. Fisher, E. Michie and G. YieldingSummaryThe lack of a predictive tool for calculating fault permeability in carbonate reservoirs has led to an increasing amount of research towards the permeability structure of carbonate-hosted fault zones. However, a better understanding of fault rock distributions and their potential petrophysical properties is required to predict the impact of faults in carbonate reservoirs. This research combines structural, microstructural and petrophysical data from a series of carbonate-hosted fault zones in Malta, enabling an understanding of the fault zone permeability structures in various lithofacies, whilst highlighting the heterogeneity on all scales of carbonate-hosted fault zones. From the studied exposures, fault displacements of 30 m are required for a continuous fault core, but 100–200 m displacement is required for a continuous cataclasite veneer. Fault rocks have reduced macro-scale heterogeneity compared to host rocks, whilst the outcrop scale heterogeneity is increased. Fault rock permeability measurements show that permeability is reduced relative to the host rock for all faulted lithofacies. Cataclasite exhibits the lowest permeability (geometric average = 10−3 mD). These reductions are large enough to have a noticeable impact on fluid flow over production scales for the c.60% of high porosity fault rocks, however less than 10% of fault rocks derived from low porosity host rocks exhibit these permeability reductions. 30% of fault rocks derived from high porosity host rocks exhibit permeability reductions sufficient to behave as a significant barrier to fluid flow.
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Impact of Laboratory-Induced Deformation and Naturally-Occurring Faults on Fluid Flow in Carbonates
Authors I. Kaminskaite, Q.J. Fisher and E.H. MichieSummaryFaults were studied in a broad range of carbonates and cover all carbonate rock types from Dunham classification: from mudstones to crystalline, with porosities ranging from <1 to 52%. Protolith samples were used for the triaxial testing. Laboratory-deformed and naturally-faulted samples were compared with the host rocks in a petrophysical, macrostructural and microstructural sense. The results show that transition from dilatant to compactive cataclastic flow in carbonates occurs at the porosity of c.10%. Samples with porosity <10% typically dilate during failure and show an increase in permeability after the deformation, whereas samples with porosity >10% compact and show reduced permeability. Deformation bands formed in outcrops with carbonates with a porosity >50% may form significant barriers to fluid flow because cataclasis is often accompanied by recrystallization and cementation which could not be produced in the laboratory. Fault cores in low-porosity outcrops (<1%) consisting of cataclasites and cemented chaotic breccias may form seals to fluid flow because they reduce the permeability by up to a magnitude of 6 and are not cross-cut by fractures. Transitional shear planes or breccias formed both in the laboratory and in damage zones of naturally-formed fault zones show enhanced fracture connectivity, which creates conduits to flow.
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Integrated Assessment of InSAR and Passive Seismic Monitoring, Addressing Caprock Integrity within a SAGD Project
Authors C. Hindriks, S. Azri, K. Bisdom and R. RahmouneSummaryThis extended abstract describes a study explaining and demonstrating a method to identify spatial and temporal changes in fault stability from a combined assessment of InSAR and micro-seismic monitoring data. The method uses reservoir deformation inferred from InSAR data to stochastically model a micro-seismic catalogue which is compared to the measured catalogue. Discrepancies and variations in space and time between the modeled and measured catalogue are addressed by variations in stochastic parameters that are related to fault proximity, fault activation and reservoir strain. Knowledge on the transient behavior of these parameters aid in highlighting high risk zones and planning for future reservoir development options.
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Fault Architecture, an Integrated Study
More LessSummaryFault geometric attributes and fault rock properties are essential components of fault seal analysis and understanding the fluid flow within faulted reservoirs. Therefore, studying the fault geometry and properties are important for different applications such as petroleum exploration and production, CO2 storage, and geothermal energy management. We use an integrated approach to provide a more realistic geometry and architecture of faults. In this approach, fault imaging through seismic attributes is integrated with comparable outcrop studies. Using frequency decomposition and choosing higher frequency seismic data for the attribute analysis, we image faults beyond seismic resolution. Our data covers both siliciclastic and carbonate rocks. Utilizing the compiled fault geometric attributes data measured on outcrop and seismic and comparing them with the previously published data; we investigate the fault scaling relations. The scaling relations are to predict fault dimensions and to better understand the fault growth mechanism. This will reduce the uncertainty related to fault prediction in any kind of reservoir.
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Top Seal Understanding by Integrating 3D Resistivity with Seismic and Wells: Lessons from Gulf of Mexico
Authors V. Ricoy-Paramo and F. RothSummaryThis work illustrates three representative cases of the integration of 3D CSEM derived resistivity with seismic data within the top seal section with the aim of investigating the resistivity response of top seals that (i) have failed, (ii) work, and (iii) are leaky but can still contain hydrocarbons in the prospect. In the past 10 years, CSEM has been used in exploration programs of various offshore basins throughout the world where many wells have been drilled. Although CSEM data have too low resolution to determine the properties close or at the seal reservoir interface, we are getting information from the bulk rock properties of the top seal rock lithology. This has provided a significant number of case examples where the resistivity of the top seal section can be investigated and related to exploration outcome. This integration has shed light on typical patterns of expressions of seismic and resistivity for discoveries vs. failures. We present three such case examples and conclude that the integration of resistivity with seismic allows to enhance our understanding of top seal by providing information on fluid distribution and containment.
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Seismic Fault Damage Zone Characterisation for Reservoir Modelling Using Advanced Attribute Analysis
Authors C. Botter and A. ChampionSummaryFaults play a key role in reservoir connectivity by enhancing or restricting fluid flow. While seismic data is one the main ways of subsurface investigation, faults are still interpreted as surfaces as their internal structure is often at the limit of seismic resolution. In order to populate reservoir models of fault volumes using fault facies techniques, we introduce an innovative seismic attribute analysis to characterise fault core and damage zone from undamaged surrounding rocks in siliclastic settings. We use a total horizontal derivative attribute in addition to the standard seismic attributes applied to fault analyses, and use statistical methods to establish the outer limits of the damage zone. We apply our workflow in porous silisclastic normal faulting in the Thebe Gas Field, Exmouth Plateau of the Canarvon basin, offshore Northwest Australia. Based on this analysis, we are able to define seismic facies calibrated with well and analogue data that can be used for spatial conditioning of fault-facies based reservoir modelling. Our work provide a visual and quantitative tool to define the internal structure of the fault damage zone in order to model fluid flow more accurately in reservoir grids.
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Strain and Flow Pathways in a Shale Fault Zone: An In-Situ Test of Fault Seal Integrity
Authors P. Henry, Y. Guglielmi, C. Gout, R. Castilla, P. Dick, F. Donzé, A. Tsopela, D. Neyens, L. De Barros and J. DurandSummaryA series of small scale (decametric) injection tests were performed in a small fault at IRSN Tournemire underground laboratory in Toarcian shales. Pressure, induced strains and flow rate were monitored at the injection borehole. Monitoring systems comprising strain sensors and a resistivity streamer were installed in observation boreholes within the fluid invaded zone. A micro-seismic network was also deployed. This experiment shows complex interactions between flow and strain as both appear to be distributed between major discontinuities and the fracture network in the damage and core zones. Permeability variations can be approximated as exponential functions of fluid pressure, with different coefficients below and above a threshold, defining the Fracture Opening Pressure. Hydraulic opening is typically associated with dilatant shearing of fractures. However, the associated strain appears small and largely reversible. Rupture on the main fault plane is triggered after several hours of injection, resulting in a permanent change of flow pathways and flow rate. Numerical modeling based on these experimental results suggest fluid channeling along a fault zone could occur in the subcritical Coulomb regime without fault activation at the larger scale.
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Significance of Fault Seal in Assessing CO2 Storage Capacity and Leakage Risks - An Example from Offshore Norway
Authors L. Wu, R. Thorsen, P. Ringrose, S. Ottesen and K. HartvedtSummaryUnderstanding of fault seal is crucial for assessing the storage capacity and leakage risks of a CO2 storage site, as it can significantly impact the project on across-fault and along-fault migration/leakage risking, as well as reservoir pressure predictions. Here we present a case study from Smeaheia offshore Norway to illustrate the importance of fault seal assessment. Leakage risk assessment has been systematically conducted for Smeaheia using the Evidence Support Logic and the Bow-tie methodologies. The results show that the Alpha structure has low across-fault and along-fault leakage risks, thus has a potential value to be added as extra volume for the CO2 storage project. The Beta structure shows large fault-related leakage risks, since it is a 3-way closure juxtaposed to the faulted/fractured Precambrian basement, with large uncertainties of across-fault and along-fault permeabilities of the Øygarden Fault Zone. Fault seal analysis of the relay ramps along the Vette Fault Zone shows that the Smeaheia site can be affected by the pressure drawdown from Troll depletion. However, Smeaheia also has pressure recharging potential from sea bed through Quaternary sediments. Regional dynamic modelling with input from fault seal studies and new pressure measurements can help narrow the storage capacity uncertainty window.
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Deep Galerkin Model in Batchflow
Authors A. Koryagin and S. TsimferSummaryRecently, a lot of papers proposed to use neural networks to approximately solve partial differential equations (PDEs). Yet, there has been a lack of flexible framework for convenient experimentation. In an attempt to fill the gap, we introduce a DEEPGALERKIN-model from BATCHFLOW-framework, open-sourced on GITHUB. Coupled with capabilities of BATCHFLOW, DEEPGALERKIN-model allows to 1) solve partial differential equations from a large family, including heat equation and wave equation 2 ) easily search for the best neural-network architecture among the zoo, that includes RESNET and DENSENET 3) fully control the process of model-training by testing different point- sampling schemes. With that in mind, our main contribution goes as follows: implementation of a ready-to-use and open-source numerical solver of PDEs of a novel format, based on neural networks.
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3D Pore Pressure Analysis for Seal Risk Identification
Authors N. Ordonez Pérez, C. Cobos, F. Obregon and G. Zamora ValcarceSummarySeals represent barriers with different pressures at either sides of the sealing feature (no matter if it is a fault, a slide surface or a change in lithology or facies). Therefore recognizing changes in pressure becomes a strong tool to identify sealing zones and possible traps.
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Advanced Geomechanical Techniques for Natural Fracture Prediction
Authors J.C. Menescal, Y. Bezerra, J.A. Souza, A. Hussein, R. Plateaux, X. Garcia, T. Falcao, A. Rodriguez, L. Maertan and R. StohlerSummaryCarbonate rock reservoirs can be complex and difficult to model. Different processes can affect porosity and permeability during and after deposition. Post deposition process includes diagenesis ( Okubo et al. 2015 ) and deformation related to faults and bending ( Giuffrida et al. 2019 ). Most of the reservoirs are somehow deformed due to multiple processes that occurs in geological time. In carbonate rocks this deformation can act opening or closing fractures, generating conducts or baffles that controls fluids flow behaviour ( Pimenta et al. 2013 ). Because of this impact, modelling 3-D fracture networks has become a critical step for fluid flow simulation. In this paper, it is proposed the use of an advanced workflow which incorporates natural fracture prediction techniques blending with structural restoration and geomechanical forward modelling concepts to evaluate the fractures distribution and then use it to build a fracture model to a giant oil field in Campos Basin, Brazil. The studied reservoir consists mostly of oolitic grainstones from Quissamã Formation deposited on a carbonate platform similar to the rocks described by Okubo et al. (2015) . The reservoir structure is a raft generated by the carbonate platform break above the moving salt ( Vendeville and Jackson 1992 ).
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Top Seal Undrained Pore Pressure Response - Sensitivity to Skempton’s A
Authors M. Duda, R.M. Holt and J.F. StenebråtenSummaryChange of pore pressure in a reservoir modifies stress state in the reservoir itself and in its surrounding, which may further cause an undrained pore pressure response in reservoir’s overburden governed by Skempton’s parameters A and B. This sensitivity study aims to determine the importance of Skempton’s parameter A, often assumed to be 1/3 as predicted by isotropic linear elasticity, and explores the consequences of including experimental, angle-dependent values of this parameter in geomodelling. A top seal shale, assumed to be a representative example of impermeable overburden rocks, has been laboratory-tested in undrained conditions with different stress paths, i.e. ratios between the maximum and the minimum principal stresses. The results of the experimental data analysis have been used to model Skempton’s parameter A distribution and resultant undrained pore pressure response in an existing oil reservoir’s top seal. The modelling indicates that Skempton’s A values computed for a real reservoir geometry and stress state differ significantly from the typically assumed 1/3. The resultant differences in the undrained pore pressure response are significant and usually largest in the direct proximity of fault zones, suggesting that including anisotropic Skempton’s A in geomodelling may help in predicting failure risk in top seal rocks.
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Impact of Fault Permeability on Geomechanical Models of CO2 Injection in the Petrel Sub-basin, Northern Australia
Authors D. Dewhurst, Y. Zhang, P. Schaubs and L. StalkerSummaryThe Petrel sub-basin has been assessed as potentially suitable for the geological storage of carbon dioxide. One of the elements required in characterising an area for geological CO2 storage involves geomechanical modelling of the region. A preliminary set of simple geomechanical models were performed to evaluate the risk of fault reactivation and potential degree of uplift for CO2 injection in the Petrel Sub-basin. A number of injection scenarios were run, ranging from likely in situ injection rates (1–5 million tonnes of CO2 per year) to very large injection rates (∼80 million tonnes of CO2 per year). Overall model results suggest that injection at 1 to 5 million tonnes/year does not result in fault reactivation or host rock failure. Partial fault failure can occur at unrealistically high injection rates of 20 million tonnes/year or above. No fault reactivation occurs at any injection rates under strike slip stress conditions, fault reactivation only happens when the stress regime is on the normal fault-strike slip fault boundary. Varying fault permeability by up to two orders of magnitude changes modelled flow patterns, uplift and pore pressure distributions slightly but does not significantly affect fault reactivation potential.
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A Review of Deformation Bands in Carbonates
By A. CilonaSummaryDeformation bands are narrow tabular zones mm- to-cm thick, which can accommodate shear and/or volumetric strain by means of gran rearrangement, consequent pore collapse, and cataclasis. These structural features are very common in clastic sediments, but they can form also in granular carbonate media. Deformation bands can represent buffers for cross-flow and may cause compartmentalization or decrease in productivity of hydrocarbon reservoirs. This contribution presents an overview of the literature on carbonate-hosted deformation bands, compares them to the clastic hosted deformation bands and highlights the main differences between natural and laboratory deformation bands
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Pressure Equilibration Induced by Reactivation of Deep Carbonate Faults
Authors M. Lesueur, T. Poulet and M. VeveakisSummaryFluid production is known to induce stress changes in the reservoir that can be large enough to reactivate nearby dormant faults. Interestingly, following the reactivation of a fault, fluid pressure equilibration between the two sides of the fault can sometimes be observed. A sealing fault then becomes a flow channel, provoking leakage of the reservoir into the adjacent layer or fluid invasion leading to problematic early water breakthrough. In order to characterise this highly coupled, non-linear Thermo-Hydro-Mechano-Chemical (THMC) behaviour of the fault and quantify fluid invasion, we introduce a multi-scale numerical framework using the REDBACK finite element simulator. This approach links the reservoir (km) scale - implementing a poro-elastic model - to the fault-scale (m) - implementing a THMC reactivation model. The complex behaviour of the fault is upscaled into an interface law that links the stress state of the fault to its response in terms of slippage and permeability. Using this framework, we investigate the fault reactivation scenario in the case of a production from a well located next to a sealing fault in a high P,T carbonate reservoir.
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Pore Space Evolution within Carbonate Fault Rocks
Authors F. Ferraro and F. AgostaSummaryWe investigate five extensional carbonate fault zones responsible of destructive earthquakes in peninsular Italy to understand the control exerted by cataclasis and diagenesis on their petrophysical properties. The study fault rocks were exhumed from depths ≤1.5 km during Plio-Quaternary times. They are made up of calcitic and dolomitic survivor grains, carbonate matrix, and possible calcite cements. The grain-supported fault rocks localize within the outermost portions of the fault cores, whereas the matrix-supported in the innermost portions, near the main slip surfaces. By integrating the results of optical microscopy, digital image, ultrasonic, and petrophysical analyses carried out at both room and increasing confining pressures, we are able to assess the pore type, geometry, connectivity and overall network properties in the different fault rock textures. All grain-supported and dolomiterich, matrix supported fault rocks include soft, crack-like pores, which constitute well-connected connected networks. Differently, within the calcite-rich, matrix-supported fault rocks conspicuous precipitation of euhedral calcite that occurred under vadose conditions occluded the largest and well-connected pores, leaving only stiff, sub-spherical pores. The results of this work permit to establish, for the first time, the relative control exerted by deformation mechanisms and diagenetic processes on the pore characteristics in carbonate fault rocks.
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Carbonate Fault Seal: How Can we Improve its Predictability?
Authors E. Michie, Q. Fisher, B. Freeman, A. Cooke, I. Kaminskaite and G. YieldingSummaryA significant knowledge gap exists when analysing and predicting the behaviour of faults within carbonate reservoirs. To improve this, a large database of carbonate fault rock properties has been collected as part of a consortium led by the University of Leeds and Badleys. This Carbonate Fault Rock project has been successful in discovering key controls on fault rock development, including their petrophysical properties. Many tens of faults within carbonates have been analysed from a range of lithofacies, tectonic regimes, burial depths and displacements, and porosity and permeability measurements from over 300 samples have been made, with the goal to find trends controlling fault rock development. Factors have been examined to assess their control on fault rock permeabilities, such as tectonic regime, displacement, depth of burial, host lithofacies, lithofacies juxtaposition, host porosity and host permeability. The results show which factors have the more significant influence on fault rock properties, and are used to generate a predictive algorithm to compute fault permeability and transmissibility multipliers in carbonate reservoir models.
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