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  • 1
    Digitale Medien
    Digitale Medien
    An approach to combined rock physics and seismic modelling of fluid substitution effects (2002)
    Oxford, UK : Blackwell Science Ltd
    Geophysical prospecting 50 (2002), S. 0 
    Details
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: The aim of seismic reservoir monitoring is to map the spatial and temporal distributions and contact interfaces of various hydrocarbon fluids and water within a reservoir rock. During the production of hydrocarbons, the fluids produced are generally displaced by an injection fluid. We discuss possible seismic effects which may occur when the pore volume contains two or more fluids. In particular, we investigate the effect of immiscible pore fluids, i.e. when the pore fluids occupy different parts of the pore volume.The modelling of seismic velocities is performed using a differential effective-medium theory in which the various pore fluids are allowed to occupy the pore space in different ways. The P-wave velocity is seen to depend strongly on the bulk modulus of the pore fluids in the most compliant (low aspect ratio) pores. Various scenarios of the microscopic fluid distribution across a gas–oil contact (GOC) zone have been designed, and the corresponding seismic properties modelled. Such GOC transition zones generally give diffuse reflection regions instead of the typical distinct GOC interface. Hence, such transition zones generally should be modelled by finite-difference or finite-element techniques.We have combined rock physics modelling and seismic modelling to simulate the seismic responses of some gas–oil zones, applying various fluid-distribution models. The seismic responses may vary both in the reflection time, amplitude and phase characteristics. Our results indicate that when performing a reservoir monitoring experiment, erroneous conclusions about a GOC movement may be drawn if the microscopic fluid-distribution effects are neglected.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2478.2002.00304.x
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  • 2
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    Improved quantitative calibration of rock physics models (2011)
    Geological Society of London
    Details
    Publikationsdatum: 2011-11-01
    Beschreibung: In reservoir characterization, rock-physics models provide the link between seismic observables (density, compressional and shear wave speeds) and reservoir parameters, such as porosity, lithology and fluid saturation. However, the accuracy of these predictions is rarely explored. In fact, the validation of a model representing a dataset is often limited to the analysis of a cross-plot of two arbitrary magnitudes. The objective of this paper is to improve the calibration procedure through a quantitative assessment of the reservoir property predictions using various rock-physics models. The analysis is based on an inverse rock-physics modelling that organizes the rock-physics transforms into constraint data so that the seismic variables are direct functions of the reservoir parameters. It is revealed that the predictions of reservoir quality can assist in the diagnosis of the rock microstructure itself, such as the location of clay particles in clay-rich sediments. In addition, we found that a quantitative analysis is the only way to evaluate accurately the performance of various models when studying heterogeneous datasets.
    Print ISSN: 1354-0793
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Publiziert von Geological Society of London
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
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    Estimation of elastic moduli of mixed porous clay composites (2011)
    Society of Exploration Geophysicists (SEG)
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    Publikationsdatum: 2011-01-01
    Beschreibung: We have developed a procedure for estimating the effective elastic properties of various mixtures of smectite and kaolinite over a range of confining pressures, based on the individual effective elastic properties of pure porous smectite and kaolinite. Experimental data for the pure samples are used as input to various rock physics models, and the predictions are compared with experimental data for the mixed samples. We have evaluated three strategies for choosing the initial properties in various rock physics models: (1) input values have the same porosity, (2) input values have the same pressure, and (3) an average of (1) and (2). The best results are obtained when the elastic moduli of the two porous constituents are defined at the same pressure and when their volumetric fractions are adjusted based on different compaction rates with pressure. Furthermore, our strategy makes the modeling results less sensitive to the actual rock physics model. The method can help obtain the elastic properties of mixed unconsolidated clays as a function of mechanical compaction. The more common procedure for estimating effective elastic properties requires knowledge about volume fractions, elastic properties of individual constituents, and geometric details of the composition. However, these data are often uncertain, e.g., large variations in the mineral elastic properties of clays have been reported in the literature, which makes our procedure a viable alternative.
    Print ISSN: 0016-8033
    Digitale ISSN: 1942-2156
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Society of Exploration Geophysicists (SEG)
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  • 4
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    Modeling of elasticity effects of sandstone compaction using coated inclusions (2011)
    Society of Exploration Geophysicists (SEG)
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    Publikationsdatum: 2011-05-01
    Beschreibung: Compaction of siliciclastic sediments leads to an increase in their stiffness parameters and seismic velocities. Although mechanical compaction implies a reduction of porosity and closing of compliant pores, chemical compaction may alter the mineral properties, the cementing of grain contacts, and the pore volume. The ability of rock physics models to quantify such effects on seismic observables will aid hydrocarbon exploration. A framework was designed for modeling compaction effects by use of a so-called coated inclusion model that eliminates the need of using a hybrid approach through combining different theories. A basic feature of the model is that the inclusion is defined by a kernel representing the pore, which is surrounded by shells that may individually have different elastic properties from those of the pore-filling material and the background matrix. The modeling can be designed to explore seismic effects of various texture perturbations, including contact cementing and pore-filling processes. The numerical modelings seem to be consistent with the results obtained from other rock physics models. The model allows for the possibility of including small-scale heterogeneities within the rock texture and estimating frequency dispersion together with attenuation due to pore fluid flow. A basic weakness of the method is the relatively large number of parameters needed to describe a porous rock, which will always limit its practical usage. However, its basic physical foundation may provide a reference for understanding the qualitative and quantitative effects of various cementation scenarios on seismic parameters.
    Print ISSN: 0016-8033
    Digitale ISSN: 1942-2156
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Society of Exploration Geophysicists (SEG)
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  • 5
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    Surface-wave analysis for identifying unfrozen zones in subglacial sediments (2012)
    Society of Exploration Geophysicists (SEG)
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    Publikationsdatum: 2012-05-01
    Beschreibung: To reveal the extent of freezing in subglacial sediments, we estimated S-wave velocity along a glacier using surface-wave analysis. Because the S-wave velocity varies significantly with the degree of freezing of the pore fluid in the sediments, this information is useful for identifying unfrozen zones within subglacial sediments, which again is important for glacier dynamics. We used active-source multichannel seismic data originally acquired for reflection analysis along a glacier at Spitsbergen in the Norwegian Arctic and proposed an effective approach of multichannel analysis of surface waves (MASW) in a glacier environment. Common-midpoint crosscorrelation gathers were used for the MASW to improve lateral resolution because the glacier bed has a rough topology. We used multimode analysis with a genetic algorithm inversion to estimate the S-wave velocity due to the potential existence of a low-velocity layer beneath the glacier ice and the observation of higher modes in the dispersion curves. In the inversion, we included information of ice thickness derived from high-resolution ground-penetrating radar data because a simulation study demonstrated that the ice thickness was necessary to estimate accurate S-wave velocity distribution of deep subglacial sediment. The estimated S-wave velocity distribution along the seismic line indicated that low velocities occurred below the glacier, especially beneath thick ice (∼1300  m/s for ice thicknesses larger than 50 m). Because this velocity was much lower than the velocity in pure ice (∼1800  m/s), the pore fluid was partially melted at the ice–sediment interface. At the shallower subglacial sediments (ice thickness less than 50 m), the S-wave velocity was similar to that of the pure ice, suggesting that shallow subglacial sediments are more frozen than sediments beneath thick ice.
    Print ISSN: 0016-8033
    Digitale ISSN: 1942-2156
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Society of Exploration Geophysicists (SEG)
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  • 6
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    Analysis and design of quadratic parameter varying (QPV) control systems with polytopic attractive region (2018)
    Elsevier
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    Publikationsdatum: 2018-05-01
    Print ISSN: 0016-0032
    Digitale ISSN: 1879-2693
    Thema: Mathematik , Technik allgemein
    Publiziert von Elsevier
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  • 7
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    Reservoir characterization in under-balanced drilling with nonlinear Moving Horizon Estimation with manual and automatic control conditions (2020)
    Elsevier
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    Publikationsdatum: 2020-09-01
    Print ISSN: 0920-4105
    Digitale ISSN: 1873-4715
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Publiziert von Elsevier
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  • 8
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    Elastic properties as indicators of heat flux into cold near-surface Arctic sediments (2020)
    Society of Exploration Geophysicists
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    Publikationsdatum: 2020-09-01
    Beschreibung: Temperatures in the terrestrial Arctic today are increasing at the highest rate on earth, and heat flux into the cold sediments may result in extensive thawing. Thawing sediments lose their mechanical strength; therefore, warming has significant geomorphic consequences. We have combined heat flux, rock physics, and seismic modeling to estimate the change in elastic properties related to various published future climate scenarios in the Arctic, and we thus investigate the feasibility of exposing thawing rates from seismic data. The heat-flux model was validated using temperature data continuously recorded at the surface and within a well in Adventdalen, Svalbard. We estimated the evolving temperatures in an upper vertical section of the well using the heat-flux model, and we compared them with actual measured well temperatures. The modeled and measured data were consistent, even though our simplified model ignores heat transport due to fluid flow and the effects of clay. The heat-flux modeling resulted in subsurface isotherms that were input to rock-physics modeling based on two-end-member mixing of fully frozen and unfrozen composites to delineate possible climate effects on the seismic properties of the sediments. The results show that the elastic and seismic properties of (partly) frozen unconsolidated near-surface saline sediments strongly depend on heat flux into the subsurface, and they vary seasonally and between different climate scenarios. Seismic data obtained by full-waveform modeling and real experiments in Adventdalen show that time-lapse analysis of Rayleigh waves may be an efficient tool for monitoring heat flux into the terrestrial Arctic.
    Print ISSN: 0016-8033
    Digitale ISSN: 1942-2156
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Society of Exploration Geophysicists
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  • 9
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    Potential Use of Time-Lapse Surface Seismics for Monitoring Thawing of the Terrestrial Arctic (2020)
    Molecular Diversity Preservation International
    Details
    Publikationsdatum: 2020-03-09
    Beschreibung: The terrestrial Arctic is warming rapidly, causing changes in the degree of freezing of the upper sediments, which the mechanical properties of unconsolidated sediments strongly depend upon. This study investigates the potential of using time-lapse surface seismics to monitor thawing of currently (partly) frozen ground utilizing synthetic and real seismic data. First, we construct a simple geological model having an initial temperature of −5 °C, and infer constant surface temperatures of −5 °C, +1 °C, +5 °C, and +10 °C for four years to this model. The geological models inferred by the various thermal regimes are converted to seismic models using rock physics modeling and subsequently seismic modeling based on wavenumber integration. Real seismic data reflecting altered surface temperatures were acquired by repeated experiments in the Norwegian Arctic during early autumn to mid-winter. Comparison of the surface wave characteristics of both synthetic and real seismic data reveals time-lapse effects that are related to thawing caused by varying surface temperatures. In particular, the surface wave dispersion is sensitive to the degree of freezing in unconsolidated sediments. This demonstrates the potential of using surface seismics for Arctic climate monitoring, but inversion of dispersion curves and knowledge of the local near-surface geology is important for such studies to be conclusive.
    Digitale ISSN: 2076-3417
    Thema: Allgemeine Naturwissenschaft
    Publiziert von Molecular Diversity Preservation International
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  • 10
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    Seismic mapping of on-shore sediments at Andøya, Norway, deposited prior to The North-Atlantic rifting (2020)
    Society of Exploration Geophysicists
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    Publikationsdatum: 2020-10-02
    Beschreibung: Andøya is an island in the north of Norway, that on its eastern side contains a local down-faulted basin of Mesozoic sediments sheltered from erosion during subsequent periods of Pleistocene glaciation. The sediments were deposited before the North Atlantic rifting and partly overlie weathered basement. We have recently carried out seismic surveying to better understand the geometry and seismic responses of the basin system. Extensive civil infrastructure and wet mire made the study area challenging for seismic exploration. We shot the survey lines at wet mire with detonating cord during winter when the mire was frozen. During summer, we conducted seismic surveying along road shoulders with a small-scale vibrator. The seismic processing was particularly challenging due to the influence of traffic noise, heterogeneous near surface conditions, and large seismic velocity contrasts. We interpreted the seismic lines in integration with other geophysical data and well logs in order to obtain a consistent and best possible seismic model of the basin. Our interpretation indicates a reorganization of the regional paleo-stress regime which took place during the continental breakup in Eocene. In spite of severe obstacles for seismic surveying of the area, our results are honoring the robustness of the seismic method for subsurface imaging.
    Print ISSN: 2324-8858
    Digitale ISSN: 2324-8866
    Thema: Geologie und Paläontologie
    Publiziert von Society of Exploration Geophysicists
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