Applications of elastic forward modeling to seismic interpretation

Geophysics ◽  
1985 ◽  
Vol 50 (8) ◽  
pp. 1266-1272 ◽  
Author(s):  
Moshe Reshef ◽  
Dan Kosloff
Keyword(s):  
Wave Propagation ◽  
Fourier Method ◽  
Forward Modeling ◽  
Solid Model ◽  
P Waves ◽  
S Waves ◽  
Heterogeneous Structures ◽  
Head Waves ◽  
Converted Phases ◽  
Numerical Divergence

In the correct processing and interpretation of time sections gathered over complicated heterogeneous structures, acoustic assumptions no longer suffice and elastic effects need to be taken into consideration. This study presents numerical modeling results obtained with the Fourier method. Two classes of important geophysical problems were considered. The first class of problem was wave propagation in structures with both vertical and horizontal heterogeneities. Results of the calculations showed strong generation of converted phases and head waves. Generation of these phases is strongly dependent upon the velocity contrasts in the medium. The second class of problem was wave propagation in structures which contain both fluids and solids. The time sections recorded in the fluid regions again showed strong converted phases which could easily be misinterpreted as genuine acoustic reflections. The numerical results for the fluid‐solid model proved to be in agreement with physical model results. The presence of many phases on the time sections and snapshots requires that the elastic modeling method give accurate amplitudes and distinguish between P‐waves and S‐waves since otherwise their interpretation can become prohibitively complicated. In this respect, the Fourier method appears suitable because of its high accuracy and its ability to distinguish between P‐ and S‐waves through respectively applying the numerical divergence and curl.

Unusual behaviour of wave propagation in auxetic structures: P-waves on free surface and S-waves in chiral lattices with piezoelectrics

2012 ◽  
Vol 249 (7) ◽  
pp. 1339-1346 ◽  
Author(s):  
Peter G. Malischewsky ◽  
Andrea Lorato ◽  
Fabrizio Scarpa ◽  
Massimo Ruzzene
Keyword(s):  
Wave Propagation ◽  
Free Surface ◽  
P Waves ◽  
S Waves ◽  
Unusual Behaviour ◽  
Auxetic Structures

Determining and Analysis of Azimuthal Coefficients Qi for the Seismically Active Transcarpathians

2014 ◽  
pp. 30-35
Author(s):  
E. Kozlovskyy ◽  
D. Malytskyy ◽  
A. Pavlova
Keyword(s):  
Neural Network ◽  
Wave Propagation ◽  
Seismic Station ◽  
Layered Media ◽  
Velocity Model ◽  
Seismic Wave Propagation ◽  
Network Modelling ◽  
Seismic Region ◽  
P Waves ◽  
S Waves

The aim of this paper is to clarify the velocity model of the Transcarpathian seismic region. The model will further be implemented in neural-network modelling to calculate and verify the depth and distribution of earthquake foci. There has been carried out an analysis of seismic wave propagation in different directions across the Transcarpathian seismic region. Being an important parameter indicative of the direction of wave propagation in a natural medium, the azimuthal coefficient q³ has proved to be efficient in developing a training neural network set. Two methods of selecting sectors have been shown, based either on the location of a seismic station or a seismic event area. We have calculated average values of the azimuthal coefficient q³ for sectors with close values of q³ for one-, two- and three-layered media according to the depth of earthquake foci in each of the three layers. With three-layered media covering earthquake foci depths of 8,000-9,000 m, the calculations accurately reflect local seismic events in the Carpathians. An average layer thickness h and an average layer velocity v were calculated separately for each E-S pair (epicenter - seismic station). Conventional combining of layers was used as a method of calculating the third layer azimuth coefficient q³. The calculations were made for direct P-waves (similar calculations can be made for S-waves). We have suggested an interpretation of the obtained results and their practical implications. It has been demonstrated how the azimuthal coefficient can be used in analysing the parameters of media.

Extension of forward modeling phase-screen code in isotropic and anisotropic media up to critical angle

Geophysics ◽  
2007 ◽  
Vol 72 (5) ◽  
pp. SM107-SM114 ◽  
Author(s):  
James C. White ◽  
Richard W. Hobbs
Keyword(s):  
Critical Angle ◽  
Model Space ◽  
Anisotropic Media ◽  
Forward Modeling ◽  
Phase Screen ◽  
Computationally Efficient ◽  
Reflection And Transmission ◽  
Transmission Coefficients ◽  
Phase Corrections ◽  
Converted Phases

The computationally efficient phase-screen forward modeling technique is extended to allow investigation of nonnormal raypaths. The code is developed to accommodate all diffracted and converted phases up to critical angle, building on a geometric construction method. The new approach relies upon prescanning the model space to assess the complexity of each screen. The propagating wavefields are then divided as a function of horizontal wavenumber, and each subset is transformed to the spatial domain separately, carrying with it angular information. This allows both locally accurate 3D phase corrections and Zoeppritz reflection and transmission coefficients to be applied. The phase-screen code is further developed to handle simple anisotropic media. During phase-screen modeling, propagation is undertaken in the wavenumber domain where exact expressions for anisotropic phase velocities are available. Traveltimes and amplitude effects from a range of anisotropic shales are computed and compared with previous published results.

scholarly journals Source mechanisms and near-source wave propagation from broadband seismograms

1994 ◽  
Vol 37 (6) ◽  
Author(s):  
J. Virieux ◽  
A. Deschamps ◽  
J. Perrot ◽  
J. Campos
Keyword(s):  
Wave Propagation ◽  
Coordinate System ◽  
Ray Tracing ◽  
Dynamic Range ◽  
Time Derivative ◽  
Quality Data ◽  
Heterogeneous Structure ◽  
Spherical Coordinate ◽  
Seismic Rupture ◽  
Converted Phases

Recording seismic events at teleseismic distances with broadband and high dynamic range instruments provides new high-quality data that allow us to interpret in more detail the complexity of seismic rupture as well as the heterogeneous structure of the medium surrounding the source where waves are initially propagating. Wave propagation analysis is performed by ray tracing in a local cartesian coordinate system near the source and in a global spherical coordinate system when waves enter the mantle. Seismograms are constructed at each station for a propagation in a 2.5-D medium. Many phases can be included and separately analyzed; this is one of the major advantages of ray tracing compared to other wave propagation techniques. We have studied four earthquakes, the 1988 Spitak Armenia Earthquake (Ms = 6.9), the 1990 Iran earthquake (Ms = 7.7), the 1990 romanian earthquake (Ms = 5.8) and the 1992 Erzincan, Turkey earthquake (Ms = 6.8). These earthquakes exhibit in different ways the complexity of the rupture and the signature of the medium surrounding the source. The use of velocity seismograms, the time derivative of displacement, increases the difficulty of the fit between synthetic seismograms and real seismograms but provides clear evidence for a need of careful time delay estimations of the different converted phases. We find that understanding of the seismic rupture as well as the influence of the medium surrounding the source for teleseismically recorded earthquakes requires a multi-stop procedure: starting with ground displacement seismograms, one is able to give a first description of the rupture as well as of the first-order influence of the medium. Then, considering the ground velocity seismograms makes the fit more difficult to obtain but increases our sensitivity to the rupture process and early converted phases. With increasing number of worldwide broadband stations, a complex rupture description is possible independently of field observations, which can be used to check the adequacy of such complicated models.

Numerical simulation of azimuthal acoustic logging in a borehole penetrating a rock formation boundary

Geophysics ◽  
2016 ◽  
Vol 81 (3) ◽  
pp. D283-D291 ◽  
Author(s):  
Peng Liu ◽  
Wenxiao Qiao ◽  
Xiaohua Che ◽  
Xiaodong Ju ◽  
Junqiang Lu ◽  
...  
Keyword(s):  
Domain Model ◽  
P Wave ◽  
S Wave ◽  
Angle Variation ◽  
P Waves ◽  
Acoustic Logging ◽  
S Waves ◽  
Rock Formation ◽  
Logging Tool ◽  
Difference Time

We have developed a new 3D acoustic logging tool (3DAC). To examine the azimuthal resolution of 3DAC, we have evaluated a 3D finite-difference time-domain model to simulate a case in which the borehole penetrated a rock formation boundary when the tool worked at the azimuthal-transmitting-azimuthal-receiving mode. The results indicated that there were two types of P-waves with different slowness in waveforms: the P-wave of the harder rock (P1) and the P-wave of the softer rock (P2). The P1-wave can be observed in each azimuthal receiver, but the P2-wave appears only in the azimuthal receivers toward the softer rock. When these two types of rock are both fast formations, two types of S-waves also exist, and they have better azimuthal sensitivity compared with P-waves. The S-wave of the harder rock (S1) appears only in receivers toward the harder rock, and the S-wave of the softer rock (S2) appears only in receivers toward the softer rock. A model was simulated in which the boundary between shale and sand penetrated the borehole but not the borehole axis. The P-wave of shale and the S-wave of sand are azimuthally sensitive to the azimuth angle variation of two formations. In addition, waveforms obtained from 3DAC working at the monopole-transmitting-azimuthal-receiving mode indicate that the corresponding P-waves and S-waves are azimuthally sensitive, too. Finally, we have developed a field example of 3DAC to support our simulation results: The azimuthal variation of the P-wave slowness was observed and can thus be used to reflect the azimuthal heterogeneity of formations.

Seismic Wave Simulation in Fractured Media

2021 ◽  
Author(s):  
Houzhu Zhang ◽  
Jiaxuan Li ◽  
Abdulmohsen Ali
Keyword(s):  
Wave Propagation ◽  
Fractured Reservoirs ◽  
Forward Modeling ◽  
Source Rocks ◽  
Reservoir Performance ◽  
Amplitude Versus Offset ◽  
Seismic Detection ◽  
Potential Applications ◽  
Subsurface Fractures ◽  
Global Energy Supply

Abstract Fractured reservoirs, including unconventional fields, are important in global energy supply, particularly for carbonate source rocks. Fractures can influence subsurface fluid flow and the stress state of a reservoir. The knowledge about the existence of fractures, their spatial distributions, and orientations can help us optimize well productivity and reservoir performance. Seismic detection of subsurface fractures provides important measurements to remotely image field-scale fractures. In developing such technology, forward modeling of the seismic response from fractures in the reservoir provides an important alternate tool for imaging subsurface fractures. In this paper, we implement a seismic modeling algorithm which can simulate 3D wave propagation in an arbitrary background media with imbedded fractures. During modeling, the fractures are added to the background medium by linear slip theory. Examples demonstrated the impacts of fractures on the wave propagation patterns for both PP and PS waves. We also investigate the amplitude versus offset (AVO) effects caused by fractures in a layer media and lay out potential applications of forward modeling in the inversion of fracture parameters and the estimation of fluid contents.

An analytical solution to separate P‐waves and S‐waves in VSP wavefields

Geophysics ◽  
1995 ◽  
Vol 60 (4) ◽  
pp. 955-967 ◽  
Author(s):  
Hiroshi Amano
Keyword(s):  
Analytical Solution ◽  
Formal Solution ◽  
Seismic Profile ◽  
Synthetic Seismograms ◽  
Third Order ◽  
P Waves ◽  
Practical Applications ◽  
S Waves ◽  
The Third ◽  
Z Domain

An analytical solution to separate P‐waves and S‐waves in vertical seismic profile (VSP) wavefields is derived using combinations of certain terms of the formal solution for forward VSP modeling. Some practical applications of this method to synthetic seismograms and field data are investigated and evaluated. Little wave distortion is recognized, and the weak wavefield masked by dominant wavetrains can be extracted with this method. The decomposed wavefield is expressed in the frequency‐depth (f-z) domain as a linear combination of up to the third‐order differential of traces, which is approximated by trace differences in the practical separation process. In general, five traces with single‐component data are required in this process, but the same process is implemented with only three traces in the acoustic case. Two‐trace extrapolation is applied to each edge of the data gather to enhance the accuracy of trace difference. Since the formulas are developed in the f-z domain, the influence of anelasticity can be taken into account, and the calculation is carried out fast enough with the benefit of the fast Fourier transform (FFT).

Wavefield separation for borehole acoustic reflection survey using parametric decomposition and waveform inversion

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. D151-D159 ◽  
Author(s):  
Nobuyasu Hirabayashi ◽  
W. Scott Leaney
Keyword(s):  
Wave Propagation ◽  
Median Filter ◽  
Waveform Inversion ◽  
Propagation Model ◽  
Acoustic Reflection ◽  
Wavefield Separation ◽  
Parametric Decomposition ◽  
Direct Head ◽  
Head Waves ◽  
Wave Propagation Model

We have developed a wavefield separation filter for borehole acoustic reflection surveys (BARS) that uses parametric decomposition and waveform inversion, which we call the PWI filter. A BARS survey uses a sonic logging tool in a fluid-filled borehole to image near-borehole structure. Signals from a monopole or dipole source are reflected from geologic interfaces and recorded by arrays of receivers of the same tool. Because amplitudes of direct head waves and borehole modes are significantly larger than those of the event signals, wavefield separation to extract the event signals is crucial for BARS processing. The PWI filter estimates the direct head waves and borehole modes using the parametric decomposition, which is based on a 1D wave propagation model in the frequency domain. The wave-propagation model is calibrated using waveform inversion, which solves for the slowness and attenuation of the waves. The inversion is regularized using the assumption that the slowness and attenuation smoothly vary with frequency; the nonlinear system of equations is iteratively solved using the Newton method. An example of wavefield separation is shown for field data for a very fast formation for a monopole source. After using the PWI filter to separate the S-waves and direct and reflected Stoneley waves, we obtain the final filtered waveforms by further applying a median filter to separate the residual waveforms, which are not separated by the PWI filter.

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