SIMULTANEOUS INVERSION FOR S-WAVE VELOCITY DENSITY FROM THE SV-SV WAVE

Geophysics ◽  
2020 ◽  
pp. 1-50
Author(s):  
Feng Zhang
Keyword(s):  
Wave Velocity ◽  
Oil And Gas ◽  
Incident Angle ◽  
Inversion Method ◽  
S Wave ◽  
Simultaneous Inversion ◽  
Pp Wave ◽  
Velocity Information ◽  
Using Data ◽  
Two Parameters

Knowledge of shear-wave velocity ( Vs) and density ( ρ) is essential for oil and gas reservoir detection and characterization. However, reliable recovery of both parameters, especially density, from the reflected PP-wave data is a difficult issue, because this inverse problem is highly illconditioned. The reflected SV-SV wave is easier to process than the PS-wave, and can provide better estimates of Vs and ρ than the PP-wave, because it is more sensitive to these parameters than the PP-wave. I present a simultaneous inversion for Vs and ρ based on a modified approximation of the SV-SV wave reflection coefficient. The modified equation includes only two parameters (natural logarithms of Vs and ρ) to be inverted, and it has high accuracy even at large incident angles and for strong impedance contrasts. I show that simultaneous inversion based on the modified approximation is well-posed when using data of small-to-moderate incident angle (20°-30°), and the misfit function can be easily regularized. The new simultaneous inversion method is applied to a SV-SV wave prestack dataset acquired from a 2D ninecomponent survey. The field data example demonstrates that the proposed method can recover stable and high-resolution density and S-wave velocity information, which can be used to investigate rock mineral composition, porosity and fluid content.

Two-step joint PP- and PS-wave three-term amplitude-variation with offset inversion

2016 ◽  
Vol 4 (4) ◽  
pp. T613-T625 ◽  
Author(s):  
Qizhen Du ◽  
Bo Zhang ◽  
Xianjun Meng ◽  
Chengfeng Guo ◽  
Gang Chen ◽  
...  
Keyword(s):  
Reflection Coefficient ◽  
Wave Reflection ◽  
Coefficient Matrix ◽  
P Wave ◽  
Inversion Method ◽  
S Wave ◽  
Amplitude Variation ◽  
Amplitude Variation With Offset ◽  
Avo Inversion ◽  
Pp Wave

Three-term amplitude-variation with offset (AVO) inversion generally suffers from instability when there is limited prior geologic or petrophysical constraints. Two-term AVO inversion shows higher instability compared with three-term AVO inversion. However, density, which is important in the fluid-type estimation, cannot be recovered from two-term AVO inversion. To reliably predict the P- and S-waves and density, we have developed a robust two-step joint PP- and PS-wave three-term AVO-inversion method. Our inversion workflow consists of two steps. The first step is to estimate the P- and S-wave reflectivities using Stewart’s joint two-term PP- and PS-AVO inversion. The second step is to treat the P-wave reflectivity obtained from the first step as the prior constraint to remove the P-wave velocity related-term from the three-term Aki-Richards PP-wave approximated reflection coefficient equation, and then the reduced PP-wave reflection coefficient equation is combined with the PS-wave reflection coefficient equation to estimate the S-wave and density reflectivities. We determined the effectiveness of our method by first applying it to synthetic models and then to field data. We also analyzed the condition number of the coefficient matrix to illustrate the stability of the proposed method. The estimated results using proposed method are superior to those obtained from three-term AVO inversion.

scholarly journals Travel-Time Inversion Method of Converted Shear Waves Using RayInvr Algorithm

2021 ◽  
Vol 11 (8) ◽  
pp. 3571
Author(s):  
Genggeng Wen ◽  
Kuiyuan Wan ◽  
Shaohong Xia ◽  
Huilong Xu ◽  
Chaoyan Fan ◽  
...  
Keyword(s):  
Travel Time ◽  
Wave Velocity ◽  
P Wave ◽  
Inversion Method ◽  
Time Inversion ◽  
Ocean Bottom Seismometer ◽  
S Wave ◽  
S Waves ◽  
Inversion Model ◽  
Travel Time Inversion

The detailed studies of converted S-waves recorded on the Ocean Bottom Seismometer (OBS) can provide evidence for constraining lithology and geophysical properties. However, the research of converted S-waves remains a weakness, especially the S-waves’ inversion. In this study, we applied a travel-time inversion method of converted S-waves to obtain the crustal S-wave velocity along the profile NS5. The velocities of the crust are determined by the following four aspects: (1) modelling the P-wave velocity, (2) constrained sediments Vp/Vs ratios and S-wave velocity using PPS phases, (3) the correction of PSS phases’ travel-time, and (4) appropriate parameters and initial model are selected for inversion. Our results show that the vs. and Vp/Vs of the crust are 3.0–4.4 km/s and 1.71–1.80, respectively. The inversion model has a similar trend in velocity and Vp/Vs ratios with the forward model, due to a small difference with ∆Vs of 0.1 km/s and ∆Vp/Vs of 0.03 between two models. In addition, the high-resolution inversion model has revealed many details of the crustal structures, including magma conduits, which further supports our method as feasible.

scholarly journals Bayesian Time-lapse Difference Inversion Based on the exact Zoeppritz Equations with Blockiness Constraint

2020 ◽  
Vol 25 (1) ◽  
pp. 89-100
Author(s):  
Lin Zhou ◽  
Jianping Liao ◽  
Jingye Li ◽  
Xiaohong Chen ◽  
Tianchun Yang ◽  
...  
Keyword(s):  
Wave Equations ◽  
Oil And Gas ◽  
Time Lapse ◽  
Seismic Inversion ◽  
Field Application ◽  
Inversion Method ◽  
S Wave ◽  
Elastic Parameters ◽  
Zoeppritz Equations ◽  
Approximate Formulas

Accurately inverting changes in the reservoir elastic parameters that are caused by oil and gas exploitation is of great importance in accurately describing reservoir dynamics and enhancing recovery. Previously numerous time-lapse seismic inversion methods based on the approximate formulas of exact Zoeppritz equations or wave equations have been used to estimate these changes. However the low accuracy of calculations using approximate formulas and the significant calculation effort for the wave equations seriously limits the field application of these methods. However, these limitations can be overcome by using exact Zoeppritz equations. Therefore, we study the time-lapse seismic difference inversion method using the exact Zoeppritz equations. Firstly, the forward equation of time-lapse seismic difference data is derived based on the exact Zoeppritz equations. Secondly, the objective function based on Bayesian inversion theory is constructed using this equation, with the changes in elastic parameters assumed to obey a Gaussian distribution. In order to capture the sharp time-lapse changes of elastic parameters and further enhance the resolution of the inversion results, the blockiness constraint, which follows the differentiable Laplace distribution, is added to the prior Gaussian background model. All examples of its application show that the proposed method can obtain stable and reasonable P- and S-wave velocities and density changes from the difference data. The accuracy of estimation is higher than for existing methods, which verifies the effectiveness and feasibility of the new method. It can provide high-quality seismic inversion results for dynamic detailed reservoir description and well location during development.

scholarly journals Estimation of S-wave velocity structure and its application to ground motion simulation

2002 ◽  
Vol 27 ◽  
Author(s):  
Basant Kafle ◽  
Hiroaki Yamanaka
Keyword(s):  
Ground Motion ◽  
Wave Velocity ◽  
Structural Model ◽  
Velocity Structure ◽  
Seismic Refraction ◽  
Inversion Method ◽  
Subsurface Structure ◽  
S Wave ◽  
Period Range ◽  
Array Measurements

Microtremor array is the most inexpensive and easy to perform technique for the estimation of S-wave velocity structure. Microtremor array measurements have been carried out in the Shizuoka Prefecture, Japan to estimate S-wave velocity structure up to the basement. Phase velocities at wide period range were determined by frequency-wavenumber spectral analysis of vertical microtremor array records. The determined phase velocity is inverted to obtain one-dimensional S-wave velocity profile by genetic algorithm inversion method. A four layer S-wave velocity model with a basement velocity of 3.5 km/s was constructed. Simulation of ground motion has been carried out with two-dimensional finite difference method. Simulation of subsurface structural model was derived from the microtremor array measurement and previous seismic refraction survey. Two profiles were taken for simulation one from Hamaoka to Ryuhyoh and another from Hamaoka to Shimada. 2-D effect of subsurface structure is observed in the propagation of ground motion in the basin. The importance of determination of 2-D subsurface structure for the estimation of ground motion is shown.

scholarly journals Inversion of the reflected SV-wave for density and S-wave velocity structures

2020 ◽  
Vol 221 (3) ◽  
pp. 1635-1639
Author(s):  
Feng Zhang ◽  
Xiang-yang Li
Keyword(s):  
Wave Velocity ◽  
Incident Angle ◽  
Seismic Exploration ◽  
S Wave ◽  
Geological Interpretation ◽  
Data Application ◽  
Essential Properties ◽  
Global Seismology ◽  
Ill Posed ◽  
Formation And Evolution

SUMMARY Density is one of the most essential properties that determines the dynamic behavior of the Earth. Besides, density has been commonly used to investigate the mineral composition, porosity and fluid content of rock. Therefore, a reliable estimation of the density structure is one of the most important objectives in both global seismology and seismic exploration. However, seismic inversions of independent density estimates are ill-posed because density has a large trade-off with velocities. Shear wave propagation is sensitive to both density and the S-wave velocity. We show that the reflected SV-wave (SV-to-SV wave) at an incident angle of 22.5o depends only on density contrast, and at incident angle 30o it depends only on S-wave velocity contrast. Thus, density as well as S-wave velocity can be directly inverted from the reflected SV-wave as separate and independent parameters. The forward modelling has high accuracy, the inverse problem is well-posed and the misfit function can be easily regularized. Field data application demonstrates the proposed method can efficiently recover reliable and high-resolution density and S-wave velocity of fine sturctures. Thus, this method has great potential in geological interpretation including understanding regional Moho structure, crustal and mantle formation and evolution, and rock lithologic composition and fluid-filled porosity.

SH-SH wave inversion for S-wave velocity and density

Geophysics ◽  
2022 ◽  
pp. 1-59
Author(s):  
Fucai Dai ◽  
Feng Zhang ◽  
Xiangyang Li
Keyword(s):  
Wave Velocity ◽  
Inversion Method ◽  
Data Sets ◽  
Sh Wave ◽  
S Wave ◽  
Data Set ◽  
Sh Waves ◽  
Model Parameter ◽  
Wave Inversion ◽  
Impedance Contrast

SS-waves (SV-SV waves and SH-SH waves) are capable of inverting S-wave velocity ( VS) and density ( ρ) because they are sensitive to both parameters. SH-SH waves can be separated from multicomponent data sets more effectively than the SV-SV wave because the former is decoupled from the PP-wave in isotropic media. In addition, the SH-SH wave can be better modeled than the SV-SV wave in the case of strong velocity/impedance contrast because the SV-SV wave has multicritical angles, some of which can be quite small when velocity/ impedance contrast is strong. We derived an approximate equation of the SH-SH wave reflection coefficient as a function of VS and ρ in natural logarithm variables. The approximation has high accuracy, and it enables the inversion of VS and ρ in a direct manner. Both coefficients corresponding to VS and ρ are “model-parameter independent” and thus there is no need for prior estimate of any model parameter in inversion. Then, we developed an SH-SH wave inversion method, and demonstrated it by using synthetic data sets and a real SH-SH wave prestack data set from the west of China. We found that VS and ρ can be reliably estimated from the SH-SH wave of small angles.

Simultaneous inversion of PP and PS seismic data

Geophysics ◽  
2006 ◽  
Vol 71 (3) ◽  
pp. R1-R10 ◽  
Author(s):  
Helene Hafslund Veire ◽  
Martin Landrø
Keyword(s):  
Seismic Data ◽  
Reservoir Characterization ◽  
Model Building ◽  
Joint Inversion ◽  
P Wave ◽  
Inversion Method ◽  
System Of Equations ◽  
S Wave ◽  
Data Set ◽  
Simultaneous Inversion

Elastic parameters derived from seismic data are valuable input for reservoir characterization because they can be related to lithology and fluid content of the reservoir through empirical relationships. The relationship between physical properties of rocks and fluids and P-wave seismic data is nonunique. This leads to large uncertainties in reservoir models derived from P-wave seismic data. Because S- waves do not propagate through fluids, the combined use of P-and S-wave seismic data might increase our ability to derive fluid and lithology effects from seismic data, reducing the uncertainty in reservoir characterization and thereby improving 3D reservoir model-building. We present a joint inversion method for PP and PS seismic data by solving approximated linear expressions of PP and PS reflection coefficients simultaneously using a least-squares estimation algorithm. The resulting system of equations is solved by singular-value decomposition (SVD). By combining the two independent measurements (PP and PS seismic data), we stabilize the system of equations for PP and PS seismic data separately, leading to more robust parameter estimation. The method does not require any knowledge of PP and PS wavelets. We tested the stability of this joint inversion method on a 1D synthetic data set. We also applied the methodology to North Sea multicomponent field data to identify sand layers in a shallow formation. The identified sand layers from our inverted sections are consistent with observations from nearby well logs.

Upper crustal velocity structure of Pearl River Delta, China, derived from dense-array observations of ambient noise

2020 ◽  
Author(s):  
Zuoyong Lyu ◽  
Xiuwei Ye ◽  
Jinshui Lyu ◽  
Xiang Zhang ◽  
Liwei Wang ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Pearl River Delta ◽  
Ambient Noise ◽  
River Delta ◽  
Tectonic Activity ◽  
Pearl River ◽  
Inversion Method ◽  
S Wave ◽  
The Pearl River ◽  
Velocity Zone

<p>The Pearl River Delta, located in the middle of the southeast coast of south China, is a graben basin. Although this region is considered tectonically relatively inactive, many small earthquakes still occur, and multi groups of faults with different directions are well developed. To better understand the geological structures in this region, we use about 30 days of ambient noise data from 88 portable stations and 38 permanent broadband stations to obtain a high-resolution 3D upper crustal S-wave velocity model. Over 3700 Inter-station group-velocity curves were measured in the 1-10 s period range and tomographically inverted by a direct surface wave inversion method in a 0.05°×0.05°grid. The checkerboard test shows that the tomographic final resolution is 0.1°×0.1°. Our results show that in the shallow crust of the study area, the velocity distribution corresponds to surface geology and geological features. The Huizhou-Dongguan depression and the Pearl River mouth exhibit low S-wave velocity feature, while the high S-wave velocity zone corresponds to the distribution of Mesozoic granite. Some faults are almost between low velocity and high velocity zone, which may play an important role of the channel of magmatic activity. The upper crustal structure in this area is closely related to the intense magmatic tectonic activity and crustal extension since Mesozoic.</p>

Direct nonlinear inversion of multiparameter 1D elastic media using the inverse scattering series

Geophysics ◽  
2009 ◽  
Vol 74 (6) ◽  
pp. WCD15-WCD27 ◽  
Author(s):  
Haiyan Zhang ◽  
Arthur B. Weglein
Keyword(s):  
Wave Velocity ◽  
Material Properties ◽  
Value Added ◽  
P Wave ◽  
Added Value ◽  
Inversion Method ◽  
Elastic Media ◽  
Nonlinear Inversion ◽  
Model Matching ◽  
S Wave

In the direct nonlinear inversion method and in algorithms for 1D elastic media, P-wave velocity, S-wave velocity, and density are depth dependent. “Direct nonlinear” means that the method uses explicit formulas that (1) input data and directly output changes in material properties without the need for indirect procedures such as model matching, searching, optimization, or other assumed aligned objectives or proxies and that (2) the algorithms recognize and directly invert the intrinsic nonlinear relationship between changes in material properties and the recorded reflection wavefields. To achieve full elastic inversion, all components of data (such as PP, SP, and SS data) are needed. The method assumes that only data and reference medium propertiesare input, and terms in the inverse series for moving mislocated reflectors resulting from the linear inverse term are separated from amplitude correction terms. Although in principle this direct inversion approach requires all components of elastic data, synthetic tests indicate that a consistent value-added result may be achieved given only PP data measurements, as long as the PP data are used to approximately synthesize the PS and SP components. Further value would be derived from measuring all components of the data as the method requires. If all components of data are available, one consistent method can solve for all of the second terms (the first terms beyond linear). The explicit nonlinear inversion formulas provide an unambiguous data requirement message as well as conceptual and practical added value beyond both linear approaches and all indirect methods.

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