Searched for: author%3A%22Mulder%2C+W.A.%22
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Minisini, S. (author), Zhebel, E. (author), Kononov, A. (author), Mulder, W.A. (author)
Modeling and imaging techniques for geophysics are extremely demanding in terms of computational resources. Seismic data attempt to resolve smaller scales and deeper targets in increasingly more complex geologic settings. Finite elements enable accurate simulation of time-dependent wave propagation in heterogeneous media. They are more costly...
journal article 2013
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Kazei, V.V. (author), Kashtan, B.M. (author), Troyan, V.N. (author), Mulder, W.A. (author)
It is generally believed that full waveform inversion needs very low frequencies in the data to avoid convergence to a local minimum, which would lead to an incorrect velocity model. Often, low frequencies are not present in the data. Then, a kinematically accurate initial model is required that contains the long-wavelength structures that...
conference paper 2013
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Moghaddam, P.P. (author), Keers, H. (author), Herrmann, F.J. (author), Mulder, W.A. (author)
Waveform inversion is the method of choice for determining a highly heterogeneous subsurface structure. However, conventional waveform inversion requires that the wavefield for each source is computed separately. This makes it very expensive for realistic 3D seismic surveys. Source-encoding waveform inversion, in which the sources are modeled...
journal article 2013
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Mulder, W.A. (author)
Migration velocity analysis with the wave equation can be accomplished by focusing of extended migration images, obtained by introducing a subsurface offset or shift. A reflector in the wrong velocity model will show up as a curve in the extended image. In the correct model, it should collapse to a point. The usual approach to obtain a focused...
conference paper 2012
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Poor Moghaddam, P. (author), Mulder, W.A. (author)
The classic least-squares cost functional for full waveform inversion suffers from local minima due to loop skipping in the absence of low frequencies in the seismic data. Velocity model building based on subsurface spatial or temporal shifts may break down in the presence of multiples in the data. Cost functionals that translate this idea to...
conference paper 2012
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Mulder, W.A. (author)
Since most of the easy hydrocarbon reservoirs have been found, accurate sub-surface imaging for oil and gas exploration and production is crucial. Seismic data can provide a band-limited reconstruction of impedance contrasts between different rock formations as well as a subsurface velocity model. Current compute power allows for the use of the...
conference paper 2012
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Minisini, S. (author), Mulder, W.A. (author), Zhebel, E. (author), Kononov, A. (author)
Abstract only.
conference paper 2012
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Wirianto, M. (author), Mulder, W.A. (author), Slob, E.C. (author)
In the application of controlled source electromagnetics for reservoir monitoring on land, the timelapse signal measured with a surface-to-surface acquisition can reveal the lateral extent on the surface of resistivity changes at depth in a hydrocarbon reservoir under production. However, a direct interpretation of the time-lapse signal may...
conference paper 2012
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Kazei, V.V. (author), Ponomarenko, A.V. (author), Troyan, V.N. (author), Kashtan, B.M. (author), Mulder, W.A. (author)
Full waveform inversion suffers from local minima, due to a lack of low frequencies in the data. A reflector below the zone of interest may, however, help in recovering the long-wavelength components of a velocity perturbation, as demonstrated in a paper by Mora. With the Born approximation for the perturbation in a reference model consisting of...
conference paper 2012
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Zhebel, E. (author), Minisini, S. (author), Mulder, W.A. (author)
We solve the three-dimensional acoustic wave equation, discretized on tetrahedral meshes. Two methods are considered: mass-lumped continuous finite elements and the symmetric interior-penalty discontinuous Galerkin method (SIP-DG). Combining the spatial discretization with the leap-frog time-stepping scheme, which is second-order accurate and...
conference paper 2012
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Zhebel, E. (author), Minisini, S. (author), Kononov, A. (author), Mulder, W.A. (author)
The finite-difference method is widely used for time-domain modelling of the wave equation because of its ease of implementation of high-order spatial discretization schemes, parallelization and computational efficiency. However, finite elements on tetrahedral meshes are more accurate in complex geometries near sharp interfaces. We compared the...
conference paper 2012
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Kononov, A. (author), Minisini, S. (author), Zhebel, E. (author), Mulder, W.A. (author)
Finite-element modelling of seismic wave propagation on tetrahedra requires meshes that accurately follow interfaces between impedance contrasts or surface topography and have element sizes proportional to the local velocity. We explain a mesh generation approach by example. Starting from a finite-difference representation of the velocity model,...
conference paper 2012
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Minisini, S. (author), Zhebel, E. (author), Kononov, A. (author), Mulder, W.A. (author)
The spreading adoption of computationally intensive techniques such as Reverse Time Migration and Full Waveform Inversion increases the need of efficiently solving the three-dimensional wave equation. Common finite-difference discretization schemes lose their accuracy and efficiency in complex geological settings with discontinuities in the...
conference paper 2012
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Kavian, M. (author), Slob, E.C. (author), Mulder, W.A. (author)
Macroscopic measurements of electrical resistivity require frequency-dependent effective models that honor the microscopic effects observable in macroscopic measurements. Effective models based on microscopic physics exist alongside with empirical models. We adopted an empirical model approach to modify an existing physical model. This provided...
journal article 2012
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Kavian, M. (author), Slob, E.C. (author), Mulder, W.A. (author)
We measured the electric parameters for four different configurations of unconsolidated homogeneous and layered sands as a function of frequency, water saturation, and salinity under fluid flow conditions. Our objective is to determine if the effect of heterogeneities at scales much smaller than the skin depth can be captured by introducing...
journal article 2011
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Wirianto, M. (author), Mulder, W.A. (author), Slob, E.C. (author)
In the application of controlled source electromagnetics for reservoir monitoring on land, repeatability errors in the source will mask the time-lapse signal due to hydrocarbon production when recording surface data close to the source. We demonstrate that at larger distances, the airwave will still provide sufficient illumination of the target....
journal article 2011
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Wirianto, M. (author), Mulder, W.A. (author), Slob, E.C. (author)
journal article 2010
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Slob, E.C. (author), Hunziker, J.W. (author), Mulder, W.A. (author)
journal article 2010
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Hak, B. (author), Mulder, W.A. (author)
Seismic data enable imaging of the Earth, not only of velocity and density but also of attenuation contrasts. Unfortunately, the Born approximation of the constant-density visco-acoustic wave equation, which can serve as a forward modelling operator related to seismic migration, exhibits an ambiguity when attenuation is included. Different...
journal article 2010
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Van Leeuwen, T. (author), Mulder, W.A. (author)
Wave-equation traveltime tomography tries to obtain a subsurface velocity model from seismic data, either passive or active, that explains their traveltimes. A key step is the extraction of traveltime differences, or relative phase shifts, between observed and modelled finite-frequency waveforms. A standard approach involves a correlation of the...
journal article 2010
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