Reflection seismology over azimuthally anisotropic media

Geophysics ◽  
1988 ◽  
Vol 53 (3) ◽  
pp. 304-313 ◽  
Author(s):  
Leon Thomsen
Keyword(s):  
Field Data ◽  
Shear Waves ◽  
Azimuthal Anisotropy ◽  
Reflection Seismology ◽  
Reflection Amplitude ◽  
Seismic Shear ◽  
Fracture Intensity ◽  
Survey Line ◽  
Vsp Data ◽  
High Vertical Resolution

Recent surveys have shown that azimuthal anisotropy (due most plausibly to aligned fractures) has an important effect on seismic shear waves. Previous work had discussed these effects on VSP data; the same effects are seen in surface recording of reflections at small to moderate angles of incidence. The anisotropic effects on different polarization components of vertically traveling shear waves permit the recognition and estimation of very small degrees of azimuthal anisotropy (of order ⩾1 percent), as in an interferometer. Anisotropic effects on traveltime yield estimates of anisotropy which are averages over large depth intervals. Often, raw field data must be corrected for these effects before the reflectors may be imaged; two variations of a rotational algorithm to determine the “principal time series” are derived. Anisotropic effects on moveout lead to abnormal moveout unless the survey line is parallel to the fractures. Anisotropic effects on reflection amplitude permit the recognition and estimation of anisotropy (hence fracture intensity) differences at the reflecting horizon, i.e., with high vertical resolution.

Interpretation of total wave‐field data over Lost Hills field, Kern County, California

Geophysics ◽  
1989 ◽  
Vol 54 (11) ◽  
pp. 1420-1429 ◽  
Author(s):  
S. G. Squires ◽  
C. D. Y. Kim ◽  
D. Y. Kim
Keyword(s):  
Wave Field ◽  
Shear Wave ◽  
Delay Time ◽  
Field Data ◽  
P Wave ◽  
Kern County ◽  
Fracture Orientation ◽  
Total Wave ◽  
Fracture Intensity ◽  
Vsp Data

Approximately 5 miles (8 km) of total wave‐field data were acquired by Production Geophysical Services (then Kim Tech., Inc.), using the OMNIPULSE® Multi‐mode Shear‐wave Generator source over the southern end of Lost Hills field, Kern County, California. The quality of the shear‐wave sections was excellent. They represent a significant improvement over conventional P‐wave sections from the area in that they provide better reflection continuity and imaging of the Lost Hills anticline. A multicomponent VSP, which was acquired close to the line, provided crucial P‐wave to S‐wave correlation, as well as fracture information. [Formula: see text] ratios computed from interval times ranged from 2.79 to 1.63. An anomalously low [Formula: see text] ratio of 1.65 in the zone of interest (Lower Reef Ridge to McDonald shale), confirmed by multicomponent VSP data, corresponds to the producing interval. Evidence of shear‐wave splitting due to azimuthal anisotropy was observed, so the SV‐wave and SH‐wave data sets were rotated into principal‐component axes of N45E for S1 and N45W for S2. The predominant fracture orientation changes from N45E at depth to N45W near the surface. This change in fracture orientation with depth was confirmed by multicomponent VSP data. Delay‐time ratios (used as a measure of fracture intensity) ranged from a maximum of 11.71 percent to a minimum of −5.48 percent across the structure. These ratios are interpreted to show changes in fracture intensity and orientation across the structure. Delay‐time ratios in the zone of interest were anomalously high (1.55–6.53 percent). Comparison of fracture intensity on the flanks of the structure with that on the crest indicates that the flanks have undergone greater deformation than the crest. The total wave‐field data set and associated analyses have provided significant structural and stratigraphic information on the Miocene Monterey formation over the Lost Hills field, highlighting the productive interval.

S *

1984 ◽  
Vol 74 (1) ◽  
pp. 61-78
Author(s):  
P. R. Gutowski ◽  
F. Hron ◽  
D. E. Wagner ◽  
S. Treitel
Keyword(s):  
Field Data ◽  
Shear Waves ◽  
Grazing Incidence ◽  
Point Sources ◽  
Seismic Exploration ◽  
Source Depth ◽  
Positive Maximum ◽  
Elastic Boundary ◽  
Vertical Changes ◽  
Common Situation

Abstract The interesting and common situation of shallow point sources close to the free surface can be modeled using an explicit elastic finite difference procedure. If the source depth is less than the predominant wavelength from the surface or other well-defined elastic boundary, then shear waves S*, are generated with an amplitude which depends strongly on the source depth. As the source depth is decreased, the amplitude of the resulting shear wave increases exponentially and the particle motion is confined to a plane perpendicular to the direction of propagation. These shear waves radiate from a point on the boundary directly above the source with a radiation pattern that is zero at grazing incidence, rises to a positive maximum at about 55° from the vertical, changes polarity, and increases negatively until merging with the PS wave. Since the use of shallow explosive sources for seismic exploration is favorable for the generation of S*, we present a field data case as an illustration.

scholarly journals Effects of Underground Cavities on the Frequency Spectrum of Seismic Shear Waves

2014 ◽  
Vol 2014 ◽  
pp. 1-17 ◽  
Author(s):  
G. Lancioni ◽  
R. Bernetti ◽  
E. Quagliarini ◽  
L. Tonti
Keyword(s):  
Frequency Spectrum ◽  
Ad Hoc ◽  
Parametric Design ◽  
Shear Waves ◽  
Scattering Problem ◽  
Ground Surface ◽  
Ground Level ◽  
Seismic Shear ◽  
Underground Cavities ◽  
Free Wave Propagation

A numerical method is proposed to study the scattering of seismic shear waves induced by the presence of underground cavities in homogeneous soils. The method is based on the superposition of two solutions: the solution of the free-wave propagation problem in a uniform half-space, easily determined analytically, and the solution of the wave scattering problem due to the cave presence, evaluated numerically by means of an ad hoc code implemented by using the ANSYS Parametric Design Language. In the two-dimensional setting, this technique is applied to the case of a single cave, placed at a certain depth from the ground level. The frequency spectrum of the seismic shear oscillation on the ground surface is determined for different dimensions and depths of the cave and compared with the spectrum registered without caves. The influence of the cave dimensions and depth on the spectrum amplification is analyzed and discussed.

Specular interferometric imaging of vertical seismic profile data

2015 ◽  
Vol 3 (3) ◽  
pp. SW57-SW62 ◽  
Author(s):  
Yunsong Huang ◽  
Ruiqing He ◽  
Chaiwoot Boonyasiriwat ◽  
Yi Luo ◽  
Gerard Schuster
Keyword(s):  
Ray Tracing ◽  
Field Data ◽  
Seismic Profile ◽  
The Other ◽  
Interferometric Imaging ◽  
Profile Data ◽  
Vertical Seismic Profile ◽  
Ghost Image ◽  
Primary Image ◽  
Vsp Data

We introduce the concept of seminatural migration of multiples in vertical seismic profile (VSP) data, denoted as specular interferometric migration, in which part of the kernel is computed by ray tracing and the other part is obtained from the data. It has the advantage over standard migration of ghost reflections, in that the well statics are eliminated and the migration image is no more sensitive to velocity errors than migration of VSP primaries. Moreover, the VSP ghost image has significantly more subsurface illumination than the VSP primary image. The synthetic and field data results validate the effectiveness of this method.

Exploring the Japan Cave in Taman Hutan Raya Djuanda, Bandung Using GPR

2018 ◽  
Vol 23 (3) ◽  
pp. 377-381
Author(s):  
Widodo Widodo ◽  
Azizatun Azimmah ◽  
Djoko Santoso
Keyword(s):  
Dielectric Permittivity ◽  
Ground Penetrating Radar ◽  
Field Data ◽  
Geophysical Methods ◽  
Forward Modeling ◽  
Additional Line ◽  
Reflection Amplitude ◽  
Underground Cavities ◽  
Ground Penetrating ◽  
Synthetic Models

Investigating underground cavities is vital due to their potential for subsidence and total collapse. One of the proven geophysical methods for locating underground cavities at a shallow depth is ground penetrating radar (GPR). GPR uses contrasting dielectric permittivity, resistivity, and magnetic permeability to map the subsurface. The aim of this research is to prove that GPR can be applied to detect underground cavities in the Japan Cave of Taman Hutan Raya Djuanda, in Bandung, Indonesia. Forward modeling was performed first using three representative synthetic models before field data were acquired. The data acquisition was then conducted using a 100 MHz GPR shielded antenna with three lines of 80 m and one additional line 10 m long. The result showed a region of different reflection amplitude, which was proven to be the air-filled cavities.

THE USE OF SEISMIC SHEAR WAVES AND COMPRESSIONAL WAVES FOR LITHOLOGICAL PROBLEMS OF SHALLOW SEDIMENTS*

1984 ◽  
Vol 32 (4) ◽  
pp. 662-675 ◽  
Author(s):  
H. STUMPEL ◽  
S. KAHLER ◽  
R. MEISSNER ◽  
B. MILKEREIT
Keyword(s):  
Shear Waves ◽  
Compressional Waves ◽  
Seismic Shear ◽  
Shallow Sediments

Analysis of multiazimuthal VSP data for anisotropy and AVO

Geophysics ◽  
1999 ◽  
Vol 64 (4) ◽  
pp. 1172-1180 ◽  
Author(s):  
W. Scott Leaney ◽  
Colin M. Sayers ◽  
Douglas E. Miller
Keyword(s):  
Fractured Reservoirs ◽  
Vertical Axis ◽  
Horizontal Stress ◽  
Azimuthal Anisotropy ◽  
Carbonate Reservoir ◽  
P Wave ◽  
Fractured Reservoir ◽  
Data Set ◽  
Vsp Data ◽  
The Impact

Multioffset vertical seismic profile (VSP) experiments, commonly referred to as walkaways, enable anisotropy to be measured reliably in the field. The results can be fed into modeling programs to study the impact of anisotropy on velocity analysis, migration, and amplitude versus offset (AVO). Properly designed multioffset VSPs can also provide the target AVO response measured under optimum conditions, since the wavelet is recorded just above the reflectors of interest with minimal reflection point dispersal. In this paper, the multioffset VSP technique is extended to include multioffset azimuths, and a multiazimuthal multiple VSP data set acquired over a carbonate reservoir is analyzed for P-wave anisotropy and AVO. Direct arrival times down to the overlying shale and reflection times and amplitudes from the carbonate are analyzed. Data analysis involves a three‐term fit to account for nonhyperbolic moveout, dip, and azimuthal anisotropy. Results indicate that the overlying shale is transversely isotropic with a vertical axis of symmetry (VTI), while the carbonate shows 4–5% azimuthal anisotropy in traveltimes. The fast direction is consistent with the maximum horizontal stress orientation determined from break‐out logs and is also consistent with the strike of major faults. AVO analysis of the reflection from the top of the carbonate layer shows a critical angle reduction in the fast direction and maximum gradient in the slow direction. This agrees with modeling and indicates a greater amplitude sensitivity in the slow direction—the direction perpendicular to fracture strike. In principle, 3-D surveys should have wide azimuthal coverage to characterize fractured reservoirs. If this is not possible, it is important to have azimuthal line coverage in the minimum horizontal stress direction to optimize the use of AVO for fractured reservoir characterization. This direction can be obtained from multiazimuthal walkaways using the azimuthal P-wave analysis techniques presented.

Twelve years of vertical birefringence in nine‐component VSP data

Geophysics ◽  
2001 ◽  
Vol 66 (2) ◽  
pp. 582-597 ◽  
Author(s):  
Donald F. Winterstein ◽  
Gopa S. De ◽  
Mark A. Meadows
Keyword(s):  
Seismic Data ◽  
Azimuthal Anisotropy ◽  
Vertical Shear ◽  
S Wave ◽  
Seismic Profiles ◽  
Surface Reflection ◽  
Vertical Seismic Profiles ◽  
Reflection Seismic ◽  
San Andreas ◽  
Vsp Data

Since 1986, when industry scientists first publicly showed data supporting the presence of azimuthal anisotropy in sedimentary rock, we have studied vertical shear‐wave (S-wave) birefringence in 23 different wells in western North America. The data were from nine‐component vertical seismic profiles (VSPs) supplemented in recent years with data from wireline crossed‐dipole logs. This paper summarizes our results, including birefringence results in tabular form for 54 depth intervals in 19 of those 23 wells. In the Appendix we present our conclusions about how to record VSP data optimally for study of vertical birefringence. We arrived at four principal conclusions about vertical S-wave birefringence. First, birefringence was common but not universal. Second, birefringence ranged from 0–21%, but values larger than 4% occurred only in shallow formations (<1200 m) within 40 km of California’s San Andreas fault. Third, at large scales birefringence tended to be blocky. That is, both the birefringence magnitude and the S-wave polarization azimuth were often consistent over depth intervals of several tens to hundreds of meters but then changed abruptly, sometimes by large amounts. Birefringence in some instances diminished with depth and in others increased with depth, but in almost every case a layer near the surface was more birefringent than the layer immediately below it. Fourth, observed birefringence patterns generally do not encourage use of multicomponent surface reflection seismic data for finding fractured hydrocarbon reservoirs, but they do encourage use of crossed‐dipole logs to examine them. That is, most reservoirs were birefringent, but none we studied showed increased birefringence confined to the reservoir.

Virtual shear source makes shear waves with air guns

Geophysics ◽  
2007 ◽  
Vol 72 (2) ◽  
pp. A7-A11 ◽  
Author(s):  
Andrey Bakulin ◽  
Albena Mateeva ◽  
Rodney Calvert ◽  
Patsy Jorgensen ◽  
Jorge Lopez
Keyword(s):  
Shear Wave ◽  
Shear Waves ◽  
Shear Velocity ◽  
Velocity Profiles ◽  
Virtual Source ◽  
S Wave ◽  
Converted Wave ◽  
Source Method ◽  
Vsp Data ◽  
Walkaway Vsp

We demonstrate a novel application of the virtual source method to create shear-wave sources at the location of buried geophones. These virtual downhole sources excite shear waves with a different radiation pattern than known sources. They can be useful in various shear-wave applications. Here we focus on the virtual shear check shot to generate accurate shear-velocity profiles in offshore environments using typical acquisition for marine walkaway vertical seismic profiling (VSP). The virtual source method is applied to walkaway VSP data to obtain new traces resembling seismograms acquired with downhole seismic sources at geophone locations, thus bypassing any overburden complexity. The virtual sources can be synthesized to radiate predominantly shear waves by collecting converted-wave energy scattered throughout the overburden. We illustrate the concept in a synthetic layered model and demonstrate the method by estimating accurate P- and S-wave velocity profiles below salt using a walkaway VSP from the deepwater Gulf of Mexico.

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