- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
NARROW
GeoRef Subject
-
all geography including DSDP/ODP Sites and Legs
-
Atlantic Ocean
-
North Atlantic
-
North Sea (3)
-
-
-
Atlantic Ocean Islands
-
Shetland Islands (1)
-
-
Europe
-
Western Europe
-
Scandinavia
-
Norway (2)
-
-
United Kingdom
-
Great Britain
-
Scotland
-
Shetland Islands (1)
-
-
-
-
-
-
-
commodities
-
oil and gas fields (2)
-
petroleum (2)
-
-
geologic age
-
Cenozoic
-
Tertiary
-
Paleogene
-
Paleocene (1)
-
-
-
-
-
Primary terms
-
Atlantic Ocean
-
North Atlantic
-
North Sea (3)
-
-
-
Atlantic Ocean Islands
-
Shetland Islands (1)
-
-
Cenozoic
-
Tertiary
-
Paleogene
-
Paleocene (1)
-
-
-
-
continental shelf (2)
-
data processing (3)
-
Europe
-
Western Europe
-
Scandinavia
-
Norway (2)
-
-
United Kingdom
-
Great Britain
-
Scotland
-
Shetland Islands (1)
-
-
-
-
-
-
geophysical methods (7)
-
oil and gas fields (2)
-
petroleum (2)
-
sedimentary rocks
-
clastic rocks
-
sandstone (1)
-
-
-
underground installations (1)
-
-
sedimentary rocks
-
sedimentary rocks
-
clastic rocks
-
sandstone (1)
-
-
-
Model misspecification and bias in the least-squares algorithm: Implications for linearized isotropic AVO
Time-lapse full-waveform inversion as a reservoir-monitoring tool — A North Sea case study
Front Matter
Abstract Seismic reflection records taken across faults frequently show an overlapping of reflections from the displaced blocks. It is demonstrated that diffraction of seismic waves is a cause and the effect may be used in interpretation. Overlapping is increased if a seismic profile crosses a fault at an acute angle. Plotted dips will be inaccurate unless diffraction is taken into account. Further, the diffraction oscillation pattern will also be obtained if a reflection horizon terminates for a reason other than faulting, for example, at a wedgeout or reef edge, or at a sudden change of facies. The facts developed are demonstrated by practical examples in which attention is directed to the approximations involved in plotting the boundaries of discontinuities.
Perceptions in seismic imaging Part 2:: Reflective and diffractive contributions to seismic imaging
Interference pattern as a means of fault detection
Abstract An integral solution to the differential equations of elastodynamics is given. The solution for the displacement at any point in an isotropic homogeneous, elastic medium is obtained in terms of the initial distribution ot body forces within a given volume and the initial distribution of displacements and stresses over the bounding surface of the volume. These quantities appear in the solutions as retarded displacements, stresses, and body forces, with two types of retardation depending upon the velocities of longitudinal and transverse waves. From the integral solution the diffraction of elastic waves through large apertures bounded by opaque walls in solid materials is formulated. The incident wave motions may be either of longitudinal or transverse polarizations. The expected shear-compression interaction is obtained in the course of the computation. By analogy with optical procedure, Fraunhofer diffraction of elastic waves may be investigated as a special case. In the example of diffraction by a slit, an incident compression wave is diffracted into (1) a compression wave with the “ordinary” spatial distribution similar to that obtained in the corresponding optical problem and (2) a weaker shear wave with an “extraordinary” distribution. In the case of incident shear waves, there is obtained a diffracted shear wave with an ordinary distribution, and a possible weak compression wave with the extraordinary distribution. The presence of the diffracted compression wave depends Upon the polarization of the incident shear wave. Opacity in the Kirchhoff sense is a property of materials which are perfectly rigid.
Abstract Existing diffraction theory is often cast in such a way as to preclude a ready qualitative understanding of diffraction phenomena. This difficulty can be overcome by making simplifying but realistic approximations which permit the diffractive response of an arbitrary subsurface with point-source excitation to be obtained in a simple closed form. The main approximations are that the subsurface behaves as an acoustic medium, that its average velocity is constant, and that its reflectivity is low. An objective of this paper is to provide the field interpreter with a practical understanding of diffraction behavior.
Abstract Record sections from three-dimensional acoustic models often contain diffracted events not predictable by classical raypath theory. Several observed and calculated record sections from models of typical geologic structures such as synclines, anticlines, and faults verify this diffraction phenomenon. A careful interpretation of the character and moveout of these diffracted events is required to delineate certain portions of the geologic structures. A far-field approximation of the retarded potential equation is suitable for direct time-domain evaluation and is used to synthesize the calculated sections. The excellent comparisons between the calculated and observed record sections suggest that the mathematical modeling technique can be a useful tool for enhancing field interpretations.
Abstract A form of Kirchhoff’s wave equation is presented which is useful to the geophysicist doing an amplitudeinterpretation of seismic reflection data. A simple rearrangement of Kirchhoff’s retarded potential equation allowsthe reflection process to be evaluated as a convolution of the derivative of the source wavelet with a term called the“wavefront sweep velocity”. The wavefront sweep velocity is a measure of the rate at which the incidentwavefront covers the reflecting boundary. By comparing wavefront sweep velocities for geologic models with different curvature, one obtains an intuitive feeling forthe relation of diffraction and reflection amplitudes to boundary curvature. Also, from this convolutional form of the waveequation, the geometrical optics solution for reflection amplitude is easily obtained. But more important, from thewave-front sweep velocity approach, a graphical method evolves which allows the geophysicist to use compass and ruler toestimate the effects of curvature and diffraction on seismic amplitude.
Diffraction Response for Nonzero Separation of Source and Receiver
Abstract An existing theory based on the Kirchhoff retarded potential method makes distinctive predictions relating the amplitude characteristics of diffraction patterns to the geometry of subsurface reflectors. The application of this theory to seismic stacked sections would offer the geophysicist useful information to be included in subsurface interpretations. However, a possible barrier to such applications arises from the fact that the theory as originally put forth applies only to data recorded with zero source-receiver separation, whereas stacked sections are produced by averaging data recorded over a wide range of shot-geophone distances. To deal properly with seismic data as actually recorded. it is desirable to have a theory of diffraction amplitudes formulated for nonzero separation of source and receiver. This paper develops such a theory through an appropriate extension of the Kirch-hoff approach. By expressing the problem in a special coordinate system, the Kirchhoff integral solution of the acoustic wave equation is reduced to a time-domain convolution of the source wavelet with an operator recognized as the impulse response of the subsurface geometry under consideration. Impulse responses are computed explicitly for an infinite reflecting plane and for diffracting edges perpendicular and parallel to the source-receiver axis. The nonzero-separation theory is compared to the zero-separation theory through numerical evaluation of the relevant formulas, and the latter is shown to be a special case of the former, as it should be. More importantly, the unexpected conclusion emerges that diffraction amplitudes at nonzero source-receiver separation arc controlled almost exclusively by the location of the source-receiver midpoint. Since the data summed together in stacking all share a common shot-geophone midpoint, the diffraction amplitudes on the stacked trace should behave in good approximation to the zero-separation theory. Theoretical support is thus obtained for applying the zero-separation theory to stacked seismic data.
Abstract The author’s earlier diffraction paper (Trorey. 1970) for coincident source and receiver locations is extended to the case ofarbitrary source and receiver locations. The extension requires no additional assumptions and, as in the earlier paper, is in closedform suitable for calculations. The new resulis permit modeling of normal-moveout effects and can thus, for example, be used to studymigration before and aftei common-depth-point stacking as welt as to study common-depth-point stacking itself. In general, the pointsource/receiver response of an arbitrary subsurface with arbitrary source/receiver locations can be calculated.
Abstract A ray-theory approach is presented to analyse scattering of Rayleigh surface waves by a surface-breaking crack. The two-dimensional problem of normal incidence on an edge crack of depth J in an elastic half-space is discussed in detail. The basic diffraction mechanisms in the high-frequency range al Ihe mouth and the edge of the crack are investigated one by one on the basis of elastodynamic ray theory. The results are then superimposed to yield simple expressions Tor the back-scallered and forward-scattered Rayleigh surface waves and for the el as tody nam k s I ress-in tensity factors, in terms of reflection, transmission, and diffraction coefficients. These approximate results axe compared with exact numerical results. Ckrod agreement is observed for djA > I. where A is the wavelength of the incident surface wave. A simple formula for the inverse problem is presented, which relates the periodicity of Ihe amplitude modulation in the high-frequency range directly to the depth d of the crack.