Sinkhole detection using 2D full seismic waveform tomography

We have developed an application of 2D time-domain waveform tomography for detection of embedded sinkholes and anomalies. The measured seismic surface wavefields were inverted using a full-waveform inversion (FWI) technique, based on a finite-difference solution of 2D elastic wave equations and the Gauss-Newton inversion method. The key advantage of this approach is the ability to generate all possible wave propagation modes of seismic wavefields (body waves and Rayleigh waves) that are then compared with measured data to infer complex subsurface properties.The pressure-wave (P-wave) and shear-wave (S-wave) velocities are inverted independently and simultaneously. The FWI was applied to one synthetic and two real experimental data sets. The inversion results of synthetic data showed the useful capability of the waveform analysis in identifying an embedded void. The inversion results of real data sets showed that the waveform analysis was able to delineate (1) an embedded concrete culvert and (2) a complex profile with an embedded void and highly variable bedrock laterally and vertically. An independent invasive test (standard penetration test) was also conducted to verify the seismic test results.

Download Full-text

Direct shear-wave seismic survey in Sanhu area, Qaidam Basin, west China

The Leading Edge ◽

10.1190/tle41010047.1 ◽

2022 ◽

Vol 41 (1) ◽

pp. 47-53

Author(s):

Zhiwen Deng ◽

Rui Zhang ◽

Liang Gou ◽

Shaohua Zhang ◽

Yuanyuan Yue ◽

...

Keyword(s):

Shear Wave ◽

Reservoir Characterization ◽

Qaidam Basin ◽

P Wave ◽

Data Sets ◽

Direct Shear ◽

Subsurface Structure ◽

S Wave ◽

West China ◽

Wave Data

The formation containing shallow gas clouds poses a major challenge for conventional P-wave seismic surveys in the Sanhu area, Qaidam Basin, west China, as it dramatically attenuates seismic P-waves, resulting in high uncertainty in the subsurface structure and complexity in reservoir characterization. To address this issue, we proposed a workflow of direct shear-wave seismic (S-S) surveys. This is because the shear wave is not significantly affected by the pore fluid. Our workflow includes acquisition, processing, and interpretation in calibration with conventional P-wave seismic data to obtain improved subsurface structure images and reservoir characterization. To procure a good S-wave seismic image, several key techniques were applied: (1) a newly developed S-wave vibrator, one of the most powerful such vibrators in the world, was used to send a strong S-wave into the subsurface; (2) the acquired 9C S-S data sets initially were rotated into SH-SH and SV-SV components and subsequently were rotated into fast and slow S-wave components; and (3) a surface-wave inversion technique was applied to obtain the near-surface shear-wave velocity, used for static correction. As expected, the S-wave data were not affected by the gas clouds. This allowed us to map the subsurface structures with stronger confidence than with the P-wave data. Such S-wave data materialize into similar frequency spectra as P-wave data with a better signal-to-noise ratio. Seismic attributes were also applied to the S-wave data sets. This resulted in clearly visible geologic features that were invisible in the P-wave data.

Download Full-text

Variational Bayesian inversion of seismic attributes jointly for geologic facies and petrophysical rock properties

Geophysics ◽

10.1190/geo2019-0163.1 ◽

2020 ◽

Vol 85 (4) ◽

pp. MR213-MR233 ◽

Cited By ~ 1

Author(s):

Muhammad Atif Nawaz ◽

Andrew Curtis ◽

Mohammad Sadegh Shahraeeni ◽

Constantin Gerea

Keyword(s):

Gaussian Mixture ◽

Seismic Attributes ◽

Joint Estimation ◽

Training Data ◽

P Wave ◽

Rock Properties ◽

Inversion Method ◽

Computationally Efficient ◽

S Wave ◽

Well Data

Seismic attributes (derived quantities) such as P-wave and S-wave impedances and P-wave to S-wave velocity ratios may be used to classify subsurface volume of rock into geologic facies (distinct lithology-fluid classes) using pattern recognition methods. Seismic attributes may also be used to estimate subsurface petrophysical rock properties such as porosity, mineral composition, and pore-fluid saturations. Both of these estimation processes are conventionally carried out independent of each other and involve considerable uncertainties, which may be reduced significantly by a joint estimation process. We have developed an efficient probabilistic inversion method for joint estimation of geologic facies and petrophysical rock properties. Seismic attributes and petrophysical properties are jointly modeled using a Gaussian mixture distribution whose parameters are initialized by unsupervised learning using well-log data. Rock-physics models may be used in our method to augment the training data if the existing well data are limited; however, this is not required if sufficient well data are available. The inverse problem is solved using the Bayesian paradigm that models uncertainties in the form of probability distributions. Probabilistic inference is performed using variational optimization, which is a computationally efficient deterministic alternative to the commonly used sampling-based stochastic inference methods. With the help of a real data application from the North Sea, we find that our method is computationally efficient, honors expected spatial correlations of geologic facies, allows reliable detection of convergence, and provides full probabilistic results without stochastic sampling of the posterior distribution.

Download Full-text

Time–frequency windowing in multiparameter elastic FWI of shallow seismic wavefield

Geophysical Journal International ◽

10.1093/gji/ggaa242 ◽

2020 ◽

Vol 222 (2) ◽

pp. 1164-1177

Author(s):

Nikolaos Athanasopoulos ◽

Edgar Manukyan ◽

Thomas Bohlen ◽

Hansruedi Maurer

Keyword(s):

Wave Velocity ◽

Time Window ◽

Mass Density ◽

Waveform Inversion ◽

P Wave ◽

S Wave ◽

Time Frequency ◽

Full Waveform ◽

Shallow Seismic ◽

P Wave Velocity

SUMMARY Full-waveform inversion of shallow seismic wavefields is a promising method to infer multiparameter models of elastic material properties (S-wave velocity, P-wave velocity and mass density) of the shallow subsurface with high resolution. Previous studies used either the refracted Pwaves to reconstructed models of P-wave velocity or the high-amplitude Rayleigh waves to infer the S-wave velocity structure. In this work, we propose a combination of both wavefields using continuous time–frequency windowing. We start with the contribution of refracted P waves and gradually increase the time window to account for scattered body waves, higher mode Rayleigh waves and finally the fundamental Rayleigh wave mode. The opening of the time window is combined with opening the frequency bandwidth of input signals to avoid cycle skipping. Synthetic reconstruction tests revealed that the reconstruction of P-wave velocity model and mass density can be improved. The S-wave velocity reconstruction is still accurate and robust and is slightly benefitted by time–frequency windowing. In a field data application, we observed that time–frequency windowing improves the consistency of multiparameter models. The inferred models are in good agreement with independent geophysical information obtained from ground-penetrating radar and full-waveform inversion of SH waves.

Download Full-text

Amplitude-based misfit functions in viscoelastic full-waveform inversion applied to walk-away vertical seismic profile data

Geophysics ◽

10.1190/geo2018-0765.1 ◽

2019 ◽

Vol 84 (5) ◽

pp. B335-B351 ◽

Cited By ~ 5

Author(s):

Wenyong Pan ◽

Kristopher A. Innanen

Keyword(s):

Amplitude Ratio ◽

Waveform Inversion ◽

Seismic Profile ◽

P Wave ◽

Western Canada ◽

Full Waveform Inversion ◽

Walk Away ◽

Profile Data ◽

S Wave ◽

Full Waveform

Viscoelastic full-waveform inversion is applied to walk-away vertical seismic profile data acquired at a producing heavy-oil field in Western Canada for the determination of subsurface velocity models (P-wave velocity [Formula: see text] and S-wave velocity [Formula: see text]) and attenuation models (P-wave quality factor [Formula: see text] and S-wave quality factor [Formula: see text]). To mitigate strong velocity-attenuation trade-offs, a two-stage approach is adopted. In Stage I, [Formula: see text] and [Formula: see text] models are first inverted using a standard waveform-difference (WD) misfit function. Following this, in Stage II, different amplitude-based misfit functions are used to estimate the [Formula: see text] and [Formula: see text] models. Compared to the traditional WD misfit function, the amplitude-based misfit functions exhibit stronger sensitivity to attenuation anomalies and appear to be able to invert [Formula: see text] and [Formula: see text] models more reliably in the presence of velocity errors. Overall, the root-mean-square amplitude-ratio and spectral amplitude-ratio misfit functions outperform other misfit function choices. In the final outputs of our inversion, significant drops in the [Formula: see text] to [Formula: see text] ratio (~1.6) and Poisson’s ratio (~0.23) are apparent within the Clearwater Formation (depth ~0.45–0.50 km) of the Mannville Group in the Western Canada Sedimentary Basin. Strong [Formula: see text] (~20) and [Formula: see text] (~15) anomalies are also evident in this zone. These observations provide information to help identify the target attenuative reservoir saturated with heavy-oil resources.

Download Full-text

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

Interpretation ◽

10.1190/int-2016-0056.1 ◽

2016 ◽

Vol 4 (4) ◽

pp. T613-T625 ◽

Cited By ~ 1

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.

Download Full-text

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

Applied Sciences ◽

10.3390/app11083571 ◽

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.

Download Full-text

Elastic reflection traveltime inversion with decoupled wave equation

Geophysics ◽

10.1190/geo2017-0631.1 ◽

2018 ◽

Vol 83 (5) ◽

pp. R463-R474 ◽

Cited By ~ 6

Author(s):

Guanchao Wang ◽

Shangxu Wang ◽

Jianyong Song ◽

Chunhui Dong ◽

Mingqiang Zhang

Keyword(s):

Wave Equation ◽

Wave Velocity ◽

Waveform Inversion ◽

P Wave ◽

Model Parameters ◽

Local Minima ◽

S Wave ◽

Traveltime Inversion ◽

Velocity Models ◽

Elastic Reflection

Elastic full-waveform inversion (FWI) updates high-resolution model parameters by minimizing the residuals of multicomponent seismic records between the field and model data. FWI suffers from the potential to converge to local minima and more serious nonlinearity than acoustic FWI mainly due to the absence of low frequencies in seismograms and the extended model domain (P- and S-velocities). Reflection waveform inversion can relax the nonlinearity by relying on the tomographic components, which can be used to update the low-wavenumber components of the model. Hence, we have developed an elastic reflection traveltime inversion (ERTI) approach to update the low-wavenumber component of the velocity models for the P- and S-waves. In our ERTI algorithm, we took the P- and S-wave impedance perturbations as elastic reflectivity to generate reflections and a weighted crosscorrelation as the misfit function. Moreover, considering the higher wavenumbers (lower velocity value) of the S-wave velocity compared with the P-wave case, optimizing the low-wavenumber components for the S-wave velocity is even more crucial in preventing the elastic FWI from converging to local minima. We have evaluated an equivalent decoupled velocity-stress wave equation to ERTI to reduce the coupling effects of different wave modes and to improve the inversion result of ERTI, especially for the S-wave velocity. The subsequent application on the Sigsbee2A model demonstrates that our ERTI method with the decoupled wave equation can efficiently update the low-wavenumber parts of the model and improve the precision of the S-wave velocity.

Download Full-text

Practical concept of traveltime inversion of simulated P-wave vertical seismic profile data in weak to moderate arbitrary anisotropy

Geophysics ◽

10.1190/geo2019-0331.1 ◽

2020 ◽

Vol 85 (4) ◽

pp. C107-C123

Author(s):

Ivan Pšenčík ◽

Bohuslav Růžek ◽

Petr Jílek

Keyword(s):

Waveform Inversion ◽

Anisotropic Media ◽

Compressional Wave ◽

Seismic Profile ◽

P Wave ◽

Source Distribution ◽

S Wave ◽

Vertical Seismic Profile ◽

Weak Anisotropy ◽

Traveltime Inversion

We have developed a practical concept of compressional wave (P-wave) traveltime inversion in weakly to moderately anisotropic media of arbitrary symmetry and orientation. The concept provides sufficient freedom to explain and reproduce observed anisotropic seismic signatures to a high degree of accuracy. The key to this concept is the proposed P-wave anisotropy parameterization (A-parameters) that, together with the use of the weak-anisotropy approximation, leads to a significantly simplified theory. Here, as an example, we use a simple and transparent formula relating P-wave traveltimes to 15 P-wave A-parameters describing anisotropy of arbitrary symmetry. The formula is used in the inversion scheme, which does not require any a priori information about anisotropy symmetry and its orientation, and it is applicable to weak and moderate anisotropy. As the first step, we test applicability of the proposed scheme on a blind inversion of synthetic P-wave traveltimes generated in vertical seismic profile experiments in homogeneous models. Three models of varying anisotropy are used: tilted orthorhombic and triclinic models of moderate anisotropy (approximately 10%) and an orthorhombic model of strong anisotropy (>25%) with a horizontal plane of symmetry. In all cases, the inversion yields the complete set of 15 P-wave A-parameters, which make reconstruction of corresponding phase-velocity surfaces possible with high accuracy. The inversion scheme is robust with respect to noise and the source distribution pattern. Its quality depends on the angular illumination of the medium; we determine how the absence of nearly horizontal propagation directions affects inversion accuracy. The results of the inversion are applicable, for example, in migration or as a starting model for inversion methods, such as full-waveform inversion, if a model refinement is desired. A similar procedure could be designed for the inversion of S-wave traveltimes in anisotropic media of arbitrary symmetry.

Download Full-text

Using 2D long-streamer seismic waveform tomography to decipher sedimentary processes surrounding a forearc fault offshore Alaska

10.5194/egusphere-egu21-13056 ◽

2021 ◽

Author(s):

Amin Kahrizi ◽

Matthias Delescluse ◽

Mathieu Rodriguez ◽

Pierre-Henri Roche ◽

Anne Bécel ◽

...

Keyword(s):

Mass Transport ◽

Hanging Wall ◽

Plate Boundary ◽

Normal Fault ◽

P Wave ◽

Fault System ◽

Fault Activity ◽

Seismic Waveform ◽

Waveform Tomography ◽

Mass Transport Deposits

<p>Acoustic full-waveform inversion (FWI), or waveform tomography, involves use of both phase and amplitude of the recorded compressional waves to obtain a high-resolution P-wave velocity model of the propagation medium. Recent theoretical and computing advances now allow the application of this highly non-linear technique to field data. This led to common use of the FWI for industrial purposes related to reservoir imaging, physical properties of rocks, and fluid flow. Application of FWI in the academic domain has, so far, been limited, mostly because of the lack of adequate seismic data. Modern multichannel seismic (MCS) reflection data acquisition now&#160; have long offsets which, in some cases, enable constraining FWI-derived subsurface velocities at a significant enough depth to be useful for structural or tectonic purposes.</p><p>In this study, we show how FWI can help decipher the record of a fault activity through time at the Shumagin Gap in Alaska. The MCS data were acquired on R/V Marcus G. Langseth during the 2011 ALEUT cruise using two 8-km-long seismic streamers and a 6600 cu. in. tuned airgun array. One of the most noticeable reflection features imaged on two profiles is a large, landward-dipping normal fault in the overriding plate; a structural configuration making the area prone to generating both transoceanic and local tsunamis, including from landslides. This fault dips ~40&#176;- 45&#176;, cuts the entire crust and connects to the plate boundary fault at ~35 km depth, near the intersection of the megathrust with the forearc mantle wedge. The fault system reaches the surface at the shelf edge 75 km from the trench and forms the ~6-km deep Sanak basin. However, the record of the recent fault activity remains unclear as contouritic currents tend to be trapped by the topography created by faults, even after they are no longer active.&#160; Erosion surfaces and onlaps from contouritic processes as well as gravity collapses and mass transport deposits result in a complex sedimentary record that make it challenging to evaluate the fault activity using conventional MCS imaging alone. The long streamers used facilitated recording of refraction arrivals in the targeted continental slope area, which permitted running streamer traveltime tomography followed by FWI to produce coincident detailed velocity profiles to complement the reflection sections. We performed FWI imaging on two 40-km-long sections of the ALEUT lines crossing the Sanak basin. The images reveal low velocities of mass transport deposits as well as velocity inversions that may indicate mechanically weak layers linking some faults to gravity sliding on a d&#233;collement. One section also shows a velocity inversion in continuity to a bottom simulating reflector (BSR) only partially visible in the reflection image. The BSR velocity anomaly abruptly disappears across the main normal fault suggesting either an impermeable barrier or a lack of trapped fluids/gas in the hanging wall.</p>

Download Full-text

Data-driven Prestack Waveform Inversion Using Genetic Algorithm- Methodology and Examples

Interpretation ◽

10.1190/int-2020-0201.1 ◽

2021 ◽

pp. 1-97

Author(s):

Lingxiao Jia ◽

Subhashis Mallick ◽

Cheng Wang

Keyword(s):

Genetic Algorithm ◽

Seismic Data ◽

Waveform Inversion ◽

Seismic Inversion ◽

P Wave ◽

Data Driven ◽

Initial Model ◽

Reservoir Properties ◽

Well Control ◽

Seismic Waveform

The choice of an initial model for seismic waveform inversion is important. In matured exploration areas with adequate well control, we can generate a suitable initial model using well information. However, in new areas where well control is sparse or unavailable, such an initial model is compromised and/or biased by the regions with more well controls. Even in matured exploration areas, if we use time-lapse seismic data to predict dynamic reservoir properties, an initial model, that we obtain from the existing preproduction wells could be incorrect. In this work, we outline a new methodology and workflow for a nonlinear prestack isotropic elastic waveform inversion. We call this method a data driven inversion, meaning that we derive the initial model entirely from the seismic data without using any well information. By assuming a locally horizonal stratification for every common midpoint and starting from the interval P-wave velocity, estimated entirely from seismic data, our method generates pseudo wells by running a two-pass one-dimensional isotropic elastic prestack waveform inversion that uses the reflectivity method for forward modeling and genetic algorithm for optimization. We then use the estimated pseudo wells to build the initial model for seismic inversion. By applying this methodology to real seismic data from two different geological settings, we demonstrate the usefulness of our method. We believe that our new method is potentially applicable for subsurface characterization in areas where well information is sparse or unavailable. Additional research is however necessary to improve the compute-efficiency of the methodology.

Download Full-text