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  • 1
    Electronic Resource
    Electronic Resource
    Desert palaeofloods in central Australia (1983)
    [s.l.] : Nature Publishing Group
    Nature 301 (1983), S. 502-504 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The Finke River system (Fig. 1) heads in Archaean gneiss, granite and schist of the Arunta Block terrain about 75 km west of Alice Springs, Northern Territory, Australia. Deriving a sand and gravel load from the grussification of the Arunta rocks, the Finke transects a series of continuous ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/301502a0
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Permeability semivariograms, geological structure, and flow performance (1996)
    Springer
    Mathematical geology 28 (1996), S. 419-435 
    Details
    ISSN: 1573-8868
    Keywords: semivariograms ; sedimentary structure ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Clastic sediments may have a strong deterministic component to their permeability variation. This structure may be seen in the experimental semivariogram, but published geostatislical studies have not always exploited this feature during data analysis and covariance modeling. In this paper, we describe sedimentary organization, its importance for flow modeling, and how the semivariogram can be used for identification of structure. Clastic sedimentary structure occurs at several scales and is linked to the conditions of deposition. Lamination, bed, and bedset scales show repetitive and trend features that should be sampled carefully to assess the degree of organization and levels of heterogeneity. Interpretation of semivariograms is undertaken best with an appreciation of these geological units und how their features relate to the sampling program. Sampling at inappropriate intervals or with instruments having a large measurement volume, for example, may give misleading semivariograms. Flow simulations for models which include and ignore structure show that the repetitive features in permeability can change anisotropy and recovery performance significantly. If systematic variation is present, careful design of the permeability fields therefore is important particularly to preserve the structure effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02083654
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  • 3
    Electronic Resource
    Electronic Resource
    Permeability tensors for sedimentary structures (1994)
    Springer
    Mathematical geology 26 (1994), S. 227-250 
    Details
    ISSN: 1573-8868
    Keywords: fluid flow ; effective permeability ; tensor permeability ; sedimentary structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Accurate modeling of fluid flow through sedimentary units is of great importance in assessing the performance of both hydrocarbon reservoirs and aquifers. Most sedimentary rocks display structure from the mm or cm scale upwards. Flow simulation should therefore begin with grid blocks of this size in order to calculate effective permeabilities for larger structures. In this paper, we investigate several flow models for sandstones, and examine their impact on the calculation of effective permeability for single phase flow. Crossflow arises in some structures, in which case it may be necessary to use a tensor representation of the effective permeability. We establish conditions under which tensors are required, e.g., in crossbedded structures with a high bedding angle, high permeability contrast, and laminae of comparable thickness. Cases where the off-diagonal terms can be neglected, such as in symmetrical systems, are also illustrated. We indicate how the method of calculating tensor permeabilities may be extended to model multiphase flow in sedimentary structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02082765
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  • 4
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    Localization processes in a coupled hydrogeomechanically sensitive fractured system (2007)
    In:  Geological Society Special Publication 289: 209-225.
    Details
    Publication Date: 2007-11-05
    Description: Simulation of coupled dynamic fluid flow and geomechanical loading of fractured systems shows that complex behaviours can result, even for geometrically simple fracture systems and simple loading. Using a bi-directionally coupled simulation tool, HYDRODDA, we examine how fluids and discontinuum processes interact in a fractured, porous rock layer that is being flexed. The changes in fracture aperture, and hence the equivalent permeabilities of this system, exhibit marked localization or delocalization responses in spite of the geometrical and mechanical simplicity of this model. Typically the linked flow-deformation behaviour develops markedly non-linear responses. In some cases the permeability varies by more than three orders of magnitude for minor changes in input variables. Upscaling methods that are suitable representations of this permeability variation are developed. These non-linear behaviours develop in a porous material, which would be expected to suppress non-linear effects. If the range of behaviours seen in this geometrically simple coupled system is typical of other, potentially more complex, fully coupled systems, then the results obtained here can be used to explain the spatially and temporally high variability of the permeability characteristics of fractured systems.
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    Flow upscaling in highly heterogeneous reservoirs (2008)
    In:  Geological Society Special Publication 309: 135-144.
    Details
    Publication Date: 2008-12-16
    Description: In the early stages of field development, there are many uncertainties and the current trend is to generate coarse-scale models so that many simulations can be run rapidly in order to determine the main sensitivities in a model. However, at a later stage, more data are available and there is less uncertainty in the model, so a more detailed modelling approach is desirable. In this paper, we discuss two modelling procedures which are suitable for different stages of the life of a field, and address the problem of upscaling at each stage. First, we consider a novel approach for generating coarse-scale models for evaluating uncertainty. When there is a large amount of uncertainty, the generation of fine-scale models is too time-consuming, and upscaling them by large factors may produce large errors. We demonstrate an alternative approach for modelling at a coarse scale, while preserving the heterogeneity of the fine-scale distribution, in such a way as to reproduce the fine-scale flow results. Secondly, we focus on more detailed geological models, generated at a later stage of field development. These models may comprise millions of grid cells, and may be highly heterogeneous. Such models require upscaling, but traditional methods may be very inaccurate. We have developed a method for upscaling using well-drive boundary conditions. Tests of this method show that it can reliably reproduce the fine-scale recovery in a range of models.
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  • 6
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    A conceptual model of the relationship between channel characteristics and discharge (1979)
    Wiley
    Details
    Publication Date: 1979-01-01
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
    Published by Wiley on behalf of British Society for Geomorphology.
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  • 7
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    CO2 sequestration in a UK North Sea analogue for geological carbon storage (2013)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2013-03-22
    Description: The Fizzy discovery, a southern North Sea (UK) gas accumulation with ~50% natural CO 2 content, provides an opportunity to study the long-term quantity of CO 2 -related mineral reaction as an analogue for engineered CO 2 storage. The reservoir contains diagenetic dolomite typical of the formation; to identify and quantify any sequestration-related dolomite is challenging. To this end, CO 2 was extracted by stepwise extraction from dolomite from both the Fizzy discovery and equivalent sandstones from a low-CO 2 location. Between 0% and 22% of the dolomite in the Fizzy discovery precipitated due to the high CO 2 concentration. This corresponds to 11% ± 8% of the recent high-CO 2 charge sequestered as dolomite, a relatively low proportion after ~50 m.y. of potential CO 2 -water-rock interaction.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 8
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    Geomechanical modelling of CO2 geological storage with the use of site specific rock mechanics laboratory data (2014)
    Geological Society of London
    Details
    Publication Date: 2014-11-25
    Description: Many diverse challenges – political, economic, legal and technical – face the continued development and deployment of geological storage of anthropogenic CO 2 . Among the technical challenges will be the satisfactory proof of storage site security and efficacy. Evidence from many past geotechnical projects has shown the investigations and analyses that are required to demonstrate safe and satisfactory performance will be site specific. This will hold for the geomechanical assessment of saline aquifer storage site integrity where, compared to depleted hydrocarbon fields, there will be no previous pressure response history or rock property characterization data available. The work presented was carried out as part of a project investigating the improvement in levels of confidence in all aspects of saline aquifer site selection and characterization that could be expected with increasing data availability and in-depth analysis. Attention focused on the geomechanical modelling and the rock mechanics data used to populate models of two storage sites in geological settings analogous to those where CO 2 storage might be considered. Coupled geomechanical models were developed from reservoir simulation models initially incorporating generic rock mechanical properties and then laboratory-derived site-specific properties. The models were run in various configurations to investigate the effect of changing the rock mechanical properties on the geomechanical response of the storage systems. Modelling results showed that the pressure response at one site due to low injectivity caused significant potential for fault reactivation. Increasing the number of injection wells, thereby reducing the individual rates needed to deliver the target capacity, reduced the injection pressures and ameliorated, but did not eliminate, this adverse response.
    Print ISSN: 1354-0793
    Topics: Chemistry and Pharmacology , Geosciences
    Published by Geological Society of London
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  • 9
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    Investigation of CO2 storage in a saline formation with an angular unconformity at the caprock interface (2016)
    Geological Society of London
    Details
    Publication Date: 2016-05-14
    Description: Studies of oil reservoirs show that unconformities may occur between the reservoir and the caprock. At the boundary where the unconformity occurs, there may be a layer of higher permeability compared to the caprock. Such traps may occur at CO 2 storage sites and, therefore, their effect should be investigated. In this work, we simulate CO 2 storage beneath angular unconformities, where sandstone layers have been tilted and eroded prior to the deposition of a caprock. After preliminary studies into the effect of gridding such traps, we describe simulations of a range of 2D and 3D models. The results reveal that migration of CO 2 is influenced by the lithology beneath the unconformity, which could have been modified by weathering or diagenesis. This can have both positive and negative effects on the CO 2 storage capacity and security. It shows that an unconformity model that has a layer of high permeability at the interface between the aquifer and the caprock, as a result of weathering or diagenesis, can contribute to pressure diffusion across the reservoir. This could improve CO 2 sequestration by providing pathways for CO 2 migration to access other parts of the storage complex. However, this could also have a negative effect on the security of CO 2 storage by providing pathways for CO 2 to migrate out of the storage formation and so increase the risk of CO 2 leakage.
    Print ISSN: 1354-0793
    Topics: Chemistry and Pharmacology , Geosciences
    Published by Geological Society of London
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  • 10
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    Recovery efficiency from a turbidite sheet system: numerical simulation of waterflooding using outcrop-based geological models (2013)
    Geological Society of London
    Details
    Publication Date: 2013-05-18
    Description: A series of waterflood simulations were performed to investigate the effect of basinal position and facies permeability within a turbidite sheet system on oil recovery efficiency. Simulations used three-dimensional outcrop models of the Peïra Cava system, comprising gravel, sandstone, thin-bedded heterolithic and mudstone facies. Recovery efficiency declines with increasing permeability heterogeneity and is influenced by the interaction of vertical bed-permeability trends and flood-front gravity slumping. The occurrence of gravels with permeabilities lower than overlying sandstones produces optimum recoveries. High permeability gravels act as thief zones, enhanced by downward gravity slumping, reducing normalized recovery by up to 34 %. The effect of thief zones on recovery is related to their permeability contrast, abundance, thickness, lateral continuity, vertical position within permeable units and the permeability of underlying facies. Proximal to distal stratigraphic variations produce relatively small differences in normalized recovery of up to 13 % in models with the highest permeability heterogeneity. Differences in recovery are interpreted to reflect spatial trends in facies architecture, which determine the effectiveness of high permeability gravel thief zones. The poorest recovery is recorded from the medial model where recovery is lower than distal areas because of higher gravel abundance and thicknesses and lower compared to proximal areas because of the higher lateral continuity of gravels and underlying low-permeability mudstones.
    Print ISSN: 1354-0793
    Topics: Chemistry and Pharmacology , Geosciences
    Published by Geological Society of London
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