Elastic full-waveform inversion application using multicomponent measurements of seismic data collection

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. R63-R77 ◽  
Author(s):  
Denes Vigh ◽  
Kun Jiao ◽  
Dave Watts ◽  
Dong Sun
Keyword(s):  
Waveform Inversion ◽  
Noise Removal ◽  
Velocity Fields ◽  
Multiscale Approach ◽  
Full Waveform Inversion ◽  
Ocean Bottom ◽  
Reverse Time ◽  
Data Set ◽  
Full Waveform ◽  
Time Migration

Recent computational improvements allowed us to simulate elastic wavefields in a 3D manner and undertake the challenge of executing elastic full-waveform inversion (EFWI). The 3D SEG/EAGE overthrust synthetic data were used to run the initial tests, which included using all three components for the simulation. The inversion targeted two regions: the channel system and the overthrusted zone, which proved the effectiveness of EFWI to delineate geology in terms of [Formula: see text] and [Formula: see text] velocity fields. For the field data experiment to demonstrate the technologies, we elected to use a Gulf of Mexico ocean bottom cable data set, which allowed us to take advantage of relatively large offsets along with the 4C acquisition. The input data were minimally processed mostly through noise removal, and the initial model was a Gaussian smoothed version of grid tomography output, which is done by a prestack migrated gather flattening process. During EWFI, a multiscale approach was followed to ensure convergence, and the early stages of the [Formula: see text]/[Formula: see text] ratio were constrained by the mud rock-line ratio. When the last sets of inversions were executed, this constraint was eliminated to ensure the simultaneous update of the [Formula: see text] and [Formula: see text] velocity fields. The density was kept constant to keep the inversion at a simple level, which allowed us to draw essential conclusions. The velocity fields were validated through an imaging algorithm of the elastic reverse time migration, and the imaging shows clear structural improvements when inputting the inverted velocities in conjunction with the measurements. If full-waveform inversion can provide multiple earth parameters, the user can use the process to detect gas zones along with sand and shale content of the subsurface, which will further assist the drilling decisions. We achieved this by simulating the earth more accurately with the elastic wave propagation in the algorithms.

From classical reflectivity-to-velocity inversion to full-waveform inversion using phase-modified and deconvolved reverse time migration images

Geophysics ◽  
2017 ◽  
Vol 82 (1) ◽  
pp. S31-S49 ◽  
Author(s):  
Chen Tang ◽  
George A. McMechan
Keyword(s):  
Waveform Inversion ◽  
Time Integration ◽  
Multiscale Approach ◽  
Full Waveform Inversion ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Velocity Inversion ◽  
Full Waveform ◽  
Time Migration ◽  
Gradient Based

To obtain a physical understanding of gradient-based descent methods in full-waveform inversion (FWI), we find a connection between the FWI gradient and the image provided by reverse time migration (RTM). The gradient uses the residual data as a virtual source, and RTM uses the observed data directly as the boundary condition, so the FWI gradient is similar to a time integration of the RTM image using the residual data, which physically converts the phase of the reflectivity to the phase of the velocity. Therefore, gradient-based FWI can be connected to the classical reflectivity-to-velocity/impedance inversion (RVI). We have developed a new FWI scheme that provides a self-contained and physically intuitive derivation, which naturally establishes a connection among the amplitude-preserved RTM, the Zoeppritz equations (amplitude variation with angle inversion), and RVI, and combines them into a single framework to produce a preconditioned inversion formula. In this scheme, the relative velocity update is a phase-modified and deconvolved RTM image obtained with the residual data. Consistent with the deconvolution, the multiscale approach applies a gradually widening low-pass frequency filter to the deconvolved wavelet at early iterations, and then it uses the unfiltered deconvolved wavelet for the final iterations. Our numerical testing determined that the new method makes a significant improvement to the quality of the inversion result.

Breakthrough acquisition and technologies for subsalt imaging

Geophysics ◽  
2011 ◽  
Vol 76 (5) ◽  
pp. WB41-WB51 ◽  
Author(s):  
Denes Vigh ◽  
Jerry Kapoor ◽  
Nick Moldoveanu ◽  
Hongyan Li
Keyword(s):  
Velocity Field ◽  
Inversion Layer ◽  
Waveform Inversion ◽  
Full Waveform Inversion ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Data Set ◽  
Low Frequencies ◽  
Full Waveform ◽  
Time Migration

The recently introduced method of wide-azimuth data acquisition offers better illumination, noise attenuation, and lower frequencies to more accurately determine a velocity field for imaging. For the field data experiment to demonstrate the technologies, we used a Gulf of Mexico (GOM) wide-azimuth data set that allows us to take advantage of possible low frequencies, relatively large crossline offsets, and increased illumination. The input data was processed through true 3D azimuthal surface-related multiple elimination (SRME) with zero-phasing and debubble. Eliminating the surface-related multiples aids the velocity determination and helps uncover the subsalt sediments at the final imaging stage. After the initial velocity derivation, which was constrained to wells and geology, full-waveform inversion (FWI) was used to further update the velocity field to achieve an enhanced image. The methodology used follows the top-down approach where suprasalt sediment model is developed followed by the top of salt, salt flanks, base of salt, and finished with a limited subsalt update. To approximate the observed data by using an acoustic inversion procedure, the propagator includes effects of attenuation, anisotropy, acquisition source, and receiver depth. The geological environment is salt related, which implies that the observed data is highly elastic, even though it is input to an acoustic full waveform inversion. To use the proper constraints for the inversion, layer-stripping method is used to develop the high-resolution velocity field. The inversion stages were carefully quality controlled through gather displays to ensure the kinematics were honored. We then demonstrated the benefit of the FWI velocity field by comparing the images derived with the traditional ray-based tomographic velocity field versus the velocity field derived by FWI performing reverse time migration to produce these images. Finally, the images were compared at key well locations to evaluate the robustness of the workflow.

Efficient 3D elastic full-waveform inversion using wavefield reconstruction methods

Geophysics ◽  
2016 ◽  
Vol 81 (2) ◽  
pp. R45-R55 ◽  
Author(s):  
Espen Birger Raknes ◽  
Wiktor Weibull
Keyword(s):  
Particle Velocity ◽  
Large Scale ◽  
Waveform Inversion ◽  
Transversely Isotropic ◽  
Reconstruction Method ◽  
Full Waveform Inversion ◽  
Reverse Time ◽  
Full Waveform ◽  
Time Migration ◽  
Reconstruction Methods

In reverse time migration (RTM) or full-waveform inversion (FWI), forward and reverse time propagating wavefields are crosscorrelated in time to form either the image condition in RTM or the misfit gradient in FWI. The crosscorrelation condition requires both fields to be available at the same time instants. For large-scale 3D problems, it is not possible, in practice, to store snapshots of the wavefields during forward modeling due to extreme storage requirements. We have developed an approximate wavefield reconstruction method that uses particle velocity field recordings on the boundaries to reconstruct the forward wavefields during the computation of the reverse time wavefields. The method is computationally effective and requires less storage than similar methods. We have compared the reconstruction method to a boundary reconstruction method that uses particle velocity and stress fields at the boundaries and to the optimal checkpointing method. We have tested the methods on a 2D vertical transversely isotropic model and a large-scale 3D elastic FWI problem. Our results revealed that there are small differences in the results for the three methods.

Acoustic full waveform inversion using reflection energy: A case study from the Ekofisk LoFS ocean bottom data set

2013 ◽  
Author(s):  
Yi Wang ◽  
Kirk Wallace ◽  
Houzhu Zhang ◽  
Alexandre Bertrand ◽  
YunQing Shen
Keyword(s):  
Waveform Inversion ◽  
Full Waveform Inversion ◽  
Ocean Bottom ◽  
Data Set ◽  
Full Waveform

Efficient snapshot-free reverse time migration and computation of multiparameter gradients in full waveform inversion

Geophysics ◽  
2021 ◽  
pp. 1-79
Author(s):  
Johan O. A. Robertsson ◽  
Fredrik Andersson ◽  
René-Édouard Plessix
Keyword(s):  
Waveform Inversion ◽  
Full Waveform Inversion ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Principle Of Superposition ◽  
Model Parameter ◽  
Inversion Model ◽  
Full Waveform ◽  
Time Migration ◽  
Anisotropic Elastic

Computing images in reverse time migration and model parameter gradients from adjoint wavefields in full waveform inversion requires the correlation of a forward propagated wavefield with another reverse propagated wavefield. Although in theory only two wavefield propagations are required, one forward propagation and one reverse propagation, it requires storing the forward propagated wavefield as a function of time to carry out the correlations which is associated with significant I/O cost. Alternatively, three wavefield propagations can be carried out to reverse propagate the forward propagated wavefield in tandem with the reverse propagated wavefield. We show how highly accurate reverse time migrated images and full waveform inversion model parameter gradients for anisotropic elastic full waveform inversion can be efficiently computed without significant disk I/O using two wavefield propagations by means of the principle of superposition.

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