ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Geophone orientation and coupling in three-component sea-floor data: a case study [ Received ] (1999)
    Oxford BSL : Blackwell Science Ltd
    Geophysical prospecting 47 (1999), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: We analyse the geophone orientation and coupling in a data set from the North Sea. Based on the polarization of the water-break on the sea-floor, we have derived processing algorithms for determining the receiver orientation for gimballed and non-gimballed geophone systems. For a gimballed system, the problem reduces to a simple horizontal rotation. However, for a non-gimballed system, where all three geophone axes may vary due to varying acquisition conditions such as dipping sea-floor, twisting of recording cable, etc., the three orientation angles cannot be found directly from the recorded displacement vectors. Using the data redundancy within a common-receiver gather, a robust two-stage method is derived for the non-gimballed system in which all three orientations can initially be unknown. Testing on the North Sea data set acquired with a gimballed system shows that the three-component geophones in the data set are orientated satisfactorily within an error of 5°. However, there are some undesirable cross-couplings between the vertical and horizontal geophones, which results in leakage of shear-wave energy from the horizontal components to the vertical components.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.1999.00160.x
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Fractured reservoir delineation using multicomponent seismic data (1997)
    Oxford, U.K. and Cambridge, USA : Blackwell Science Ltd
    Geophysical prospecting 45 (1997), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The characteristic seismic response to an aligned-fracture system is shear-wave splitting, where the polarizations, time-delays and amplitudes of the split shear waves are related to the orientation and intensity of the fracture system. This offers the possibility of delineating fractured reservoirs and optimizing the development of the reservoirs using shear-wave data. However, such applications require carefully controlled amplitude processing to recover properly and preserve the reflections from the target zone. Here, an approach to this problem is suggested and is illustrated with field data.  The proposed amplitude processing sequence contains a combination of conventional and specific shear-wave processing procedures. Assuming a four-component recording (two orthogonal horizontal sources recorded by two orthogonal horizontal receivers), the split shear waves can be simulated by an effective eigensystem, and a linear-transform technique (LTT) can be used to separate the recorded vector wavefield into two principal scalar wavefields representing the fast and slow split shear waves. Conventional scalar processing methods, designed for processing P-waves, including noise reduction and stacking procedures may be adapted to process the separated scalar wavefields. An overburden operator is then derived from and applied to the post-stacked scalar wavefields. A four-component seismic survey with three horizontal wells drilled nearby was selected to illustrate the processing sequence. The field data show that vector wavefield decomposition and overburden correction are essential for recovering the reflection amplitude information in the target zone. The variations in oil production in the three horizontal wells can be correlated with the variations in shear-wave time-delays and amplitudes, and with the variations in the azimuth angle between the horizontal well and the shear-wave polarization. Dim spots in amplitude variations can be correlated with local fracture swarms encountered by the horizontal wells. This reveals the potential of shear waves for fractured reservoir delineation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.1997.3200262.x
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Interpreting non-orthogonal split shear waves for seismic anisotropy in multicomponent VSPS (1998)
    Oxford BSL : Blackwell Science Ltd
    Geophysical prospecting 46 (1998), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: There are two main sources of non-orthogonality in multicomponent shear-wave seismics: inherent non-orthogonal split shear waves arising from substantial ray deviation in off-symmetry planes due to strong anisotropy or complex overburden, and apparent non-orthogonal split shear waves in the horizontal plane due to variation of the angle of incidence even if the two shear waves along the raypath are orthogonal. Many techniques for processing shear-wave splitting in VSP data ignore these kinds of non-orthogonality of the split shear waves.Assuming inherent non-orthogonality in zero-offset VSPs, and apparent non-orthogonality in offset VSPs, we derive equations for the four-component data matrix. These can be solved by extending the linear-transform technique (LTT) to determine the shear-wave polarizations in zero-offset and offset VSPs. Both full-wave synthetic and field data are used to evaluate the technique and to examine the effects of non-orthogonal polarized split shear waves.If orthogonality is incorrectly assumed, errors in polarization measurements increase with the degree of non-orthogonality, which introduces a consistent decreasing trend in the polarization measurements. However, the effect of non-orthogonality on the estimation of geophone orientation and time delays of the two split shear waves is small and negligible in most realistic cases. Furthermore, for most cases of weak anisotropy (less than 5% shear-wave anisotropy) apparent non-orthogonality is more significant than inherent non-orthogonality. Nevertheless, for strong anisotropy (more than 10% shear-wave anisotropy) with complicated structure (tilted or inclined symmetry axis), inherent non-orthogonality may no longer be negligible.Applications to both synthetic and real data show that the extended linear-transform techniques permit accurate recovery of polarization measurements in the presence of both significant inherent and apparent non-orthogonality where orthogonal techniques often fail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.1998.750311.x
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Multicomponent near-surface correction for land VSP data (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 121 (1995), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Multicomponent seismic data collected using directional sources are degraded by the wave excitation process due to inaccurate control of the ground motion. unequal activation strengths or ground couplings between differently oriented sources, and misalignment of the pad. These acquisition uncertainties are exacerbated by the complicated near-surface scattering present in most seismic areas. Neither group of effects should be neglected in multicomponent analyses that make use of relative wavefield attributes derived from compressional and shear waves. These effects prevent analysis of the direct and reflected waves using procedures based on standard scalar techniques or a prima facia interpretation of the vector wavefield properties, even for the seemingly straightforward case of a near-offset vertical seismic profile (VSP). Near-surface correction, using a simple matrix operator designed from the shallowest recordings, alleviates many of these interpretational difficulties in near-offset VSP data. Results from application of this technique to direct waves from a nine-component VSP shot at the Conoco test-site facility, Oklahoma, are encouraging. The technique corrects for unexpected compressional-wave energy from shear-wave vibrators and collapses near-surface multiples, thus facilitating further processing for the upgoing wavefield. The method provides a simple and effective processing step for routine application to near-offset VSP analyses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1995.tb03528.x
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Linear matrix operations for multicomponent seismic processing (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 124 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Multicomponent seismic data contain overlapping information on the polarization states of distinct body-wave modes, due to the physical process of excitation, propagation and recording. This geometric redundancy should be exploited to provide an accurate separation and estimation of the wavefield attributes in order to understand the medium properly. This may be achieved using linear transforms, originally developed for separating split shear waves in four-component seismic data. These transforms separate the principal time-series components of the wavefield from the ray-path geometry and the orientation of the source and geophone axes for a uniform medium: they are deterministic and can be easily implemented.Here we reformulate the linear transforms by introducing simple geometry and medium-independent matrix operators. Although for ‘ideal’ experiments the technique may offer nothing new to the estimation of polarization that eigenanalysis cannot offer, nevertheless the formulation avoids the need to consult mathematical libraries and is useful in the interpretation of the wavefield when various inevitable acquisition-related errors dominate. Some typical problems in processing four-component data, such as the interpretation of data matrix asymmetry due to misorientations of the acquisition components and non-orthogonal polarizations for the wave components, may be easily treated and identified using a common framework with this condensed matrix form. In addition, the operation is extended to similar geometric problems in six- and nine-component data. Synthetic and field nine-component data examples are presented to illustrate the application of the matrix operations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb06363.x
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Simultaneous Refinement and Coarsening for Adaptive Meshing (1999)
    Springer
    Engineering with computers 15 (1999), S. 280-291 
    Details
    ISSN: 1435-5663
    Keywords: Key words. Adaptive meshing; Coarsening; Delaunay triangulation; Moving boundary; Refinement; Sphere packing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract. In the numerical simulation of the combustion process and microstructural evolution, we need to consider the adaptive meshing problem for a domain that has a moving boundary. During the simulation, the region ahead of the moving boundary needs to be refined (to satisfy stronger numerical conditions), and the submesh in the region behind the moving boundary should be coarsened (to reduce the mesh size). We present a unified scheme for simultaneously refining and coarsening a mesh. Our method uses sphere packings and guarantees that the resulting mesh is well-shaped and is within a constant factor of the optimal possible in the number of mesh elements. We also present several practical variations of our provably good algorithm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003660050023
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Practical Human-Machine Identification over Insecure Channels (1999)
    Springer
    Journal of combinatorial optimization 3 (1999), S. 347-361 
    Details
    ISSN: 1573-2886
    Keywords: cryptography ; human-machine identification ; network security
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Human-machine identification is an important problem in cryptography that has applications in network access, electronic commerce, and smart-card design. It is a hard problem largely because human users have a very limited capacity in memorizing secrets and in performing protocols. Therefore, in addition to the requirement that a human-machine identification scheme must be provably secure, the scheme has to be practical in the sense that it must be feasible for a human user to participate. In this paper, we develop a new scheme for this problem. Our scheme improves upon some of the previously proposed human-machine identification schemes. We present a vigorous security analysis of our scheme. We also present some attacks to show previously proposed schemes could be vulnerable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009894418895
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    facet.materialart.
    Unknown
    Simultaneous Refinement and Coarsening for Adaptive Meshing (1999)
    Springer
    Details
    Publication Date: 1999-09-13
    Print ISSN: 0177-0667
    Electronic ISSN: 1435-5663
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Published by Springer
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 9
    facet.materialart.
    Unknown
    Reservoir characterization: how can anisotropy help? (1998)
    Geological Society of London
    Details
    Publication Date: 1998-01-01
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society of London
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 10
    facet.materialart.
    Unknown
    Interpreting non-orthogonal split shear waves for seismic anisotropy in multicomponent VSPS (1998)
    Wiley
    Details
    Publication Date: 1998-01-01
    Print ISSN: 0016-8025
    Electronic ISSN: 1365-2478
    Topics: Geosciences , Physics
    Published by Wiley
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...