3D elastic full-waveform inversion for OBC data using the P-wave excitation amplitude

We have developed an efficient elastic full-waveform inversion (FWI) based on the P-wave excitation amplitude (maximum energy arrival) approximation in the source wavefields. Because, based on the P-wave excitation approximation (ExA), the gradient direction is approximated by the crosscorrelation of source and receiver wavefields at only excitation time, it estimates the gradient direction faster than its conventional counterpart. In addition to this computational speedup, the P-wave ExA automatically ignores SP and SS correlations in the approximated gradient direction. In elastic FWI for ocean bottom cable (OBC) data, the descent direction for the S-wave velocity is often degraded by undesired long-wavelength features from the SS correlation. For this reason, the P-wave excitation approach increases the convergence rate of multiparameter FWI compared with the conventional approach. The modified 2D Marmousi model with OBC acquisition is used to verify the differences between the conventional method and ExA. Finally, the feasibility of the proposed method is demonstrated on a real OBC data from the North Sea.

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Multi-parameter model building for the Qiuyue structure using four-component ocean-bottom seismometer data

Geophysics ◽

10.1190/geo2020-0537.1 ◽

2021 ◽

pp. 1-52

Author(s):

Yuzhu Liu ◽

Xinquan Huang ◽

Jizhong Yang ◽

Xueyi Liu ◽

Bin Li ◽

...

Keyword(s):

Wave Velocity ◽

Waveform Inversion ◽

Velocity Model ◽

P Wave ◽

Velocity Analysis ◽

Full Waveform Inversion ◽

Ocean Bottom ◽

Ocean Bottom Seismometer ◽

Full Waveform ◽

P Wave Velocity

Thin sand-mud-coal interbedded layers and multiples caused by shallow water pose great challenges to conventional 3D multi-channel seismic techniques used to detect the deeply buried reservoirs in the Qiuyue field. In 2017, a dense ocean-bottom seismometer (OBS) acquisition program acquired a four-component dataset in East China Sea. To delineate the deep reservoir structures in the Qiuyue field, we applied a full-waveform inversion (FWI) workflow to this dense four-component OBS dataset. After preprocessing, including receiver geometry correction, moveout correction, component rotation, and energy transformation from 3D to 2D, a preconditioned first-arrival traveltime tomography based on an improved scattering integral algorithm is applied to construct an initial P-wave velocity model. To eliminate the influence of the wavelet estimation process, a convolutional-wavefield-based objective function for the preprocessed hydrophone component is used during acoustic FWI. By inverting the waveforms associated with early arrivals, a relatively high-resolution underground P-wave velocity model is obtained, with updates at 2.0 km and 4.7 km depth. Initial S-wave velocity and density models are then constructed based on their prior relationships to the P-wave velocity, accompanied by a reciprocal source-independent elastic full-waveform inversion to refine both velocity models. Compared to a traditional workflow, guided by stacking velocity analysis or migration velocity analysis, and using only the pressure component or other single-component, the workflow presented in this study represents a good approach for inverting the four-component OBS dataset to characterize sub-seafloor velocity structures.

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Full waveform inversion of short-offset, band-limited seismic data inthe Alboran basin (SE Iberia)

10.5194/se-2019-46 ◽

2019 ◽

Author(s):

Clàudia Gras ◽

Valentí Sallarès ◽

Daniel Dagnino ◽

C. Estela Jiménez ◽

Adrià Meléndez ◽

...

Keyword(s):

Travel Time ◽

Seismic Data ◽

Waveform Inversion ◽

Velocity Model ◽

P Wave ◽

Full Waveform Inversion ◽

Time Inversion ◽

Full Waveform ◽

Travel Time Tomography ◽

Band Limited

Abstract. We present a high-resolution P-wave velocity model of the sedimentary cover and the uppermost basement until ~ 3 km depth obtained by full-waveform inversion of multichannel seismic data acquired with a 6 km-long streamer in the Alboran Sea (SE Iberia). The inherent non-linearity of the method, especially for short-offset, band-limited seismic data as this one, is circumvented by applying a data processing/modeling sequence consisting of three steps: (1) data re-datuming by back-propagation of the recorded seismograms to the seafloor; (2) joint refraction and reflection travel-time tomography combining the original and the re-datumed shot gathers; and (3) FWI of the original shot gathers using the model obtained by travel-time tomography as initial reference. The final velocity model shows a number of geological structures that cannot be identified in the travel-time tomography models or easily interpreted from seismic reflection images alone. A sharp strong velocity contrast accurately defines the geometry of the top of the basement. Several low-velocity zones that may correspond to the abrupt velocity change across steeply dipping normal faults are observed at the flanks of the basin. A 200–300 m thick, high-velocity layer embedded within lower velocity sediment may correspond to evaporites deposited during the Messinian crisis. The results confirm that the combination of data re-datuming and joint refraction and reflection travel-time inversion provides reference models that are accurate enough to apply full-waveform inversion to relatively short offset streamer data in deep water settings starting at field-data standard low frequency content of 6 Hz.

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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.

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Semiglobal viscoacoustic full-waveform inversion

Geophysics ◽

10.1190/geo2017-0773.1 ◽

2019 ◽

Vol 84 (2) ◽

pp. R271-R293 ◽

Cited By ~ 9

Author(s):

Nuno V. da Silva ◽

Gang Yao ◽

Michael Warner

Keyword(s):

Physical Properties ◽

Wave Velocity ◽

Seismic Data ◽

Waveform Inversion ◽

P Wave ◽

Full Waveform Inversion ◽

Data Set ◽

Intrinsic Attenuation ◽

Full Waveform ◽

P Wave Velocity

Full-waveform inversion deals with estimating physical properties of the earth’s subsurface by matching simulated to recorded seismic data. Intrinsic attenuation in the medium leads to the dispersion of propagating waves and the absorption of energy — media with this type of rheology are not perfectly elastic. Accounting for that effect is necessary to simulate wave propagation in realistic geologic media, leading to the need to estimate intrinsic attenuation from the seismic data. That increases the complexity of the constitutive laws leading to additional issues related to the ill-posed nature of the inverse problem. In particular, the joint estimation of several physical properties increases the null space of the parameter space, leading to a larger domain of ambiguity and increasing the number of different models that can equally well explain the data. We have evaluated a method for the joint inversion of velocity and intrinsic attenuation using semiglobal inversion; this combines quantum particle-swarm optimization for the estimation of the intrinsic attenuation with nested gradient-descent iterations for the estimation of the P-wave velocity. This approach takes advantage of the fact that some physical properties, and in particular the intrinsic attenuation, can be represented using a reduced basis, substantially decreasing the dimension of the search space. We determine the feasibility of the method and its robustness to ambiguity with 2D synthetic examples. The 3D inversion of a field data set for a geologic medium with transversely isotropic anisotropy in velocity indicates the feasibility of the method for inverting large-scale real seismic data and improving the data fitting. The principal benefits of the semiglobal multiparameter inversion are the recovery of the intrinsic attenuation from the data and the recovery of the true undispersed infinite-frequency P-wave velocity, while mitigating ambiguity between the estimated parameters.

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Seismic characterization of submarine gas-hydrate deposits in the Western Black Sea by acoustic full-waveform inversion of ocean-bottom seismic data

Geophysics ◽

10.1190/geo2018-0622.1 ◽

2019 ◽

Vol 84 (5) ◽

pp. B311-B324 ◽

Cited By ~ 1

Author(s):

Laura Gassner ◽

Tobias Gerach ◽

Thomas Hertweck ◽

Thomas Bohlen

Keyword(s):

Wave Velocity ◽

Black Sea ◽

Gas Hydrate ◽

Seismic Data ◽

Field Data ◽

Waveform Inversion ◽

P Wave ◽

Full Waveform Inversion ◽

Ocean Bottom ◽

Full Waveform

Evidence for gas-hydrate occurrence in the Western Black Sea is found from seismic measurements revealing bottom-simulating reflectors (BSRs) of varying distinctness. From an ocean-bottom seismic data set, low-resolution traveltime-tomography models of P-wave velocity [Formula: see text] are constructed. They serve as input for acoustic full-waveform inversion (FWI), which we apply to derive high-resolution parameter models aiding the interpretation of the seismic data for potential hydrate and gas deposits. Synthetic tests indicate the applicability of the FWI approach to robustly reconstruct [Formula: see text] models with a typical hydrate and gas signature. Models of S-wave velocity [Formula: see text] containing a hydrate signature can only be reconstructed when the parameter distribution of [Formula: see text] is already well-known. When we add noise to the modeled data to simulate field-data conditions, it prevents the reconstruction of [Formula: see text] completely, justifying the application of an acoustic approach. We invert for [Formula: see text] models from field data of two parallel profiles of 14 km length with a distance of 1 km. Results indicate a characteristic velocity trend for hydrate and gas occurrence at BSR depth in the first of the analyzed profiles. We find no indications for gas accumulations below the BSR on the second profile and only weak indications for hydrate. These differences in the [Formula: see text] signature are consistent with the reflectivity behavior of the migrated seismic streamer data of both profiles in which a zone of high-reflectivity amplitudes is coincident with the potential gas zone derived from the FWI result. Calculating saturation estimates for the potential hydrate and gas zones yields values of up to 30% and 1.2%, respectively.

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Full waveform inversion of marine reflection data in the plane‐wave domain

Geophysics ◽

10.1190/1.1444164 ◽

1997 ◽

Vol 62 (2) ◽

pp. 540-553 ◽

Cited By ~ 33

Author(s):

Susan E. Minkoff ◽

William W. Symes

Keyword(s):

Plane Wave ◽

Least Squares ◽

Waveform Inversion ◽

Viscoelastic Model ◽

Seismic Source ◽

P Wave ◽

Full Waveform Inversion ◽

Data Set ◽

Full Waveform ◽

Output Least Squares

Full waveform inversion of a p‐τ marine data set from the Gulf of Mexico provides estimates of the long‐wavelength P‐wave background velocity, anisotropic seismic source, and three high‐frequency elastic parameter reflectivities that explain 70% of the total seismic data and 90% of the data in an interval around the gas sand target. The forward simulator is based on a plane‐wave viscoelastic model for P‐wave propagation and primary reflections in a layered earth. Differential semblance optimization, a variant of output least‐squares inversion, successfully estimates the nonlinear P‐wave background velocity and linear reflectivities. Once an accurate velocity is estimated, output least‐squares inversion reestimates the reflectivities and an anisotropic seismic source simultaneously. The viscoelastic model predicts the amplitude‐versus‐angle trend in the data more accurately than does an elastic model. Simultaneous inversion for reflectivities and source explains substantially more of the actual data than does inversion for reflectivities with fixed source from an air‐gun modeler. The best reflectivity estimates conform to widely accepted lithologic relationships and closely match the filtered well logs.

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Optimal transport for mitigating cycle skipping in full-waveform inversion: A graph-space transform approach

Geophysics ◽

10.1190/geo2017-0807.1 ◽

2018 ◽

Vol 83 (5) ◽

pp. R515-R540 ◽

Cited By ~ 24

Author(s):

Ludovic Métivier ◽

Aude Allain ◽

Romain Brossier ◽

Quentin Mérigot ◽

Edouard Oudet ◽

...

Keyword(s):

Seismic Data ◽

Optimal Transport ◽

Waveform Inversion ◽

P Wave ◽

Imaging Method ◽

Convexity Property ◽

Full Waveform Inversion ◽

Low Frequencies ◽

Transport Distance ◽

Full Waveform

Optimal transport distance has been recently promoted as a tool to measure the discrepancy between observed and seismic data within the full-waveform-inversion strategy. This high-resolution seismic imaging method, based on a data-fitting procedure, suffers from the nonconvexity of the standard least-squares discrepancy measure, an issue commonly referred to as cycle skipping. The convexity of the optimal transport distance with respect to time shifts makes it a good candidate to provide a more convex misfit function. However, the optimal transport distance is defined only for the comparison of positive functions, while seismic data are oscillatory. A review of the different attempts proposed in the literature to overcome this difficulty is proposed. Their limitations are illustrated: Basically, the proposed strategies are either not applicable to real data, or they lose the convexity property of optimal transport. On this basis, we introduce a novel strategy based on the interpretation of the seismic data in the graph space. Each individual trace is considered, after discretization, as a set of Dirac points in a 2D space, where the amplitude becomes a geometric attribute of the data. This ensures the positivity of the data, while preserving the geometry of the signal. The differentiability of the misfit function is obtained by approximating the Dirac distributions through 2D Gaussian functions. The interest of this approach is illustrated numerically by computing misfit-function maps in schematic examples before moving to more realistic synthetic full-waveform exercises, including the Marmousi model. The better convexity of the graph-based optimal transport distance is shown. On the Marmousi model, starting from a 1D linearly increasing initial model, with data without low frequencies (no energy less than 3 Hz), a meaningful estimation of the P-wave velocity model is recovered, outperforming previously proposed optimal-transport-based misfit functions.

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Challenges in shallow targets reconstruction by 3D elastic full-waveform inversion — Which initial model?

Geophysics ◽

10.1190/geo2019-0523.1 ◽

2021 ◽

pp. 1-91

Author(s):

Daniela Teodor ◽

Cesare Cesare ◽

Farbod Khosro Anjom ◽

Romain Brossier ◽

Valentina Socco Laura ◽

...

Keyword(s):

Field Data ◽

Weighting Function ◽

Waveform Inversion ◽

P Wave ◽

Full Waveform Inversion ◽

Initial Model ◽

Near Surface ◽

Velocity Models ◽

Full Waveform ◽

3D Acquisition

Elastic full-waveform inversion (FWI) is a powerful tool for high-resolution subsurface multi-parameter characterization. However, 3D FWI applied to land data for near-surface applications is particularly challenging, since the seismograms are dominated by highly energetic, dispersive, and complex-scattered surface waves (SWs). In these conditions, a successful deterministic FWI scheme requires an accurate initial model. This study, primarily focused on field data analysis for 3D applications, aims at enhancing the resolution in the imaging of complex shallow targets, by integrating devoted SW analysis techniques with a 3D spectral-element-based elastic FWI. From dispersion curves (DCs), extracted from seismic data recorded over a sharp-interface shallow target, we built different initial S-wave (VS) and P-wave (VP) velocity models (laterally homogeneous and laterally variable), using a specific data-transform. Starting from these models, we carry out 3D FWI tests on synthetic and field data, using a relatively straightforward inversion scheme. The field data processing before FWI consists of bandpass filtering and muting of noisy traces. During FWI, a weighting function is applied to the far-offset traces. We test both 2D and 3D acquisition layouts, with different positions of the sources and variable offsets. The 3D FWI workflow enriched the overall content of the initial models, allowing a reliable reconstruction of the shallow target, especially when using laterally variable initial models. Moreover, a 3D acquisition layout guaranteed a better reconstruction of the target’s shape and lateral extension. In addition, the integration of model-oriented (preliminary monoparametric FWI) and data-oriented (time-windowing) strategies into the main optimization scheme has granted further improvement of the FWI results.

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Diffraction-angle filtering of gradient for acoustic full-waveform inversion

Geophysics ◽

10.1190/geo2019-0801.1 ◽

2020 ◽

pp. 1-87

Author(s):

Ju-Won Oh ◽

Jiubing Cheng ◽

Dong-Joo Min

Keyword(s):

Inverse Scattering ◽

Partial Derivative ◽

Waveform Inversion ◽

Weighting Factor ◽

P Wave ◽

Full Waveform Inversion ◽

Ocean Bottom ◽

The North ◽

Full Waveform ◽

Diffraction Angle

Seismic full-waveform inversion (FWI) estimates the subsurface velocity structures by reducing data misfit between observed and modeled data. Simultaneous matching of transmitted and reflected waves in seismic FWI causes different updates of different wavenumber components of a given model depending on the diffraction angle between incident and diffracted rays. Motivated by the inverse scattering imaging condition and elastic full-waveform inversion, we propose applying a diffraction-angle filtering technique in acoustic FWI, which enables us to separate transmission and reflection energy in the partial derivative wavefields. The diffraction-angle filtering is applied to the virtual source, which is the model parameter perturbation acting as a source for the partial derivative wavefields. The diffraction-angle filtering consists of two diffraction-angle filters (DAF), DAF-I and DAF-II. DAF-I, which is derived from the particle acceleration of the incidence wavefields, suppresses energies at either small or large diffraction angles by simply changing the sign of the weighting factor. DAF-I is exactly identical to the conventional inverse scattering approach. DAF-II, which is derived from the artificial shear strain of the incident P-wave, additionally suppresses energies at intermediate diffraction angles. With this mechanism, we can design various types of diffraction-angle filtering to control the updates of wavenumber components of the misfit gradient with respect to the P-wave velocity. For the synthetic Marmousi-II data and real ocean-bottom seismic data from the North Sea, we demonstrate that the diffraction-angle filtering enables us to control low-, intermediate- and high-wavenumber components of the gradient direction.

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