Velocity-model building with enhanced shallow resolution using elastic waveform inversion — An example from onshore Oman

Geophysics ◽  
2019 ◽  
Vol 84 (6) ◽  
pp. R977-R988 ◽  
Author(s):  
Carlos Pérez Solano ◽  
René-Édouard Plessix
Keyword(s):  
Elastic Property ◽  
Model Building ◽  
Waveform Inversion ◽  
Low Frequency ◽  
Velocity Model ◽  
Good Resolution ◽  
Frequency Data ◽  
Wide Aperture ◽  
Velocity Model Building ◽  
Long Offset

Full-waveform inversion is a powerful data-fitting technique that is used for velocity-model building in seismic exploration. The inversion approach exploits the sensitivity of long-offset, wide-aperture, low-frequency data to the P-wave velocity properties in the subsurface. In the geologically complex land context in which different lithologies interleave and create large elastic property contrasts, acoustic waveform inversion is challenged due to the elastic nature of the data. The large elastic property contrasts create mode conversions. At low-to-intermediate frequencies, due to tuning/interference effects, the changes in the amplitudes of the different events affect amplitude and phase of the waveforms. We found that elastic waveform inversion of the long-offset, wide-aperture, low-frequency data leads to better retrieval of the compressional velocity model than the acoustic inversion and it is more stable. To obtain a good resolution in the shallow part of the model in an efficient manner, we have developed a two-stage inversion workflow that combines offset and frequency continuation. We have evaluated the relevance of this workflow with a challenging data set from South Oman.

Low-frequency, long-offset elastic waveform inversion in the context of velocity model building

2021 ◽  
Vol 40 (5) ◽  
pp. 342-347
Author(s):  
René-Édouard Plessix ◽  
Tadas Krupovnickas
Keyword(s):  
Model Building ◽  
Waveform Inversion ◽  
Low Frequency ◽  
Real Data ◽  
Velocity Model ◽  
Acoustic Wave Propagation ◽  
Compressional Waves ◽  
Traveltime Tomography ◽  
Velocity Model Building ◽  
Long Offset

Classic imaging approaches consist of splitting the earth into background and reflectivity models. When justified, this separation of scale is quite powerful, although this approach relies on some smoothness and weak contrast assumptions. This approach allows for the imaging methods to be based on acoustic wave propagation after having identified the compressional waves through picking or signal processing. Over the past years, wave-equation tomography and waveform inversion approaches have become routine, complementing the classic approaches to derive background models. They do not rely on high-frequency picks, unlike ray-based traveltime tomography, but on low-frequency cross-correlation to define time shifts and on waveform matching. In the presence of large earth parameter contrasts, time shifts and waveforms of compressional waves may depend on elastic parameters when interferences occur within the Fresnel zones. This challenges the recovery of the background model under an acoustic assumption with low-frequency data. Accounting for an elastic propagation in waveform inversion, even in the context of model building, could help to reduce the artifacts seen in acoustic results. A synthetic and a real data example are presented to illustrate the potential benefit of using an elastic waveform inversion approach when inverting long-offset, low-frequency seismic data.

Assisting salt model building with reflection full-waveform inversion

2019 ◽  
Vol 7 (2) ◽  
pp. SB43-SB52 ◽  
Author(s):  
Adriano Gomes ◽  
Joe Peterson ◽  
Serife Bitlis ◽  
Chengliang Fan ◽  
Robert Buehring
Keyword(s):  
Model Building ◽  
Waveform Inversion ◽  
Low Frequency ◽  
Velocity Model ◽  
Full Waveform Inversion ◽  
Reflection Data ◽  
Full Waveform ◽  
Velocity Model Building ◽  
Wave Limit ◽  
Rabbit Ears

Inverting for salt geometry using full-waveform inversion (FWI) is a challenging task, mostly due to the lack of extremely low-frequency signal in the seismic data, the limited penetration depth of diving waves using typical acquisition offsets, and the difficulty in correctly modeling the amplitude (and kinematics) of reflection events associated with the salt boundary. However, recent advances in reflection FWI (RFWI) have allowed it to use deep reflection data, beyond the diving-wave limit, by extracting the tomographic term of the FWI reflection update, the so-called rabbit ears. Though lacking the resolution to fully resolve salt geometry, we can use RFWI updates as a guide for refinements in the salt interpretation, adding a partially data-driven element to salt velocity model building. In addition, we can use RFWI to update sediment velocities in complex regions surrounding salt, where ray-based approaches typically struggle. In reality, separating the effects of sediment velocity errors from salt geometry errors is not straightforward in many locations. Therefore, iterations of RFWI plus salt scenario tests may be necessary. Although it is still not the fully automatic method that has been envisioned for FWI, this combined approach can bring significant improvement to the subsalt image, as we examine on field data examples from the Gulf of Mexico.

Interpreter's Corner

2020 ◽  
Vol 39 (11) ◽  
pp. 828-833
Author(s):  
Henrik Roende ◽  
Dan Chaikin ◽  
Yi Huang ◽  
Konstantin N. Kudin
Keyword(s):  
Model Building ◽  
New Technology ◽  
Waveform Inversion ◽  
Velocity Model ◽  
Ocean Bottom ◽  
Hydrocarbon Traps ◽  
Full Waveform ◽  
Velocity Model Building ◽  
Long Offset ◽  
Set Up

The U.S. Gulf of Mexico (GoM) geology is well known for prolific structural hydrocarbon traps created by salt tectonics. In many areas, these structures lie below salt overhangs or thick canopies, requiring advanced seismic imaging to identify prospects and plan exploration wells. Ever-evolving geophysical technologies, such as 3D seismic, wide azimuth, multiwide azimuth, coil, and ocean-bottom node (OBN) acquisition designs, have unlocked the image for some of these structures over the past three decades. Recently, automatic velocity model building methods, particularly full-waveform inversion (FWI), introduced another step change in the subsalt image quality and refocused the acquisition methods on the need to acquire long-offset data. To make such a long-offset program affordable, a new survey geometry was set up with sparse OBN nodes and simultaneous shooting. The actual survey was acquired in 2019 and fully processed within 15 months from the end of the acquisition. Offsets up to 65 km were recorded, enabling FWI velocity updates down to 15 km depth. To provide the reader with a glimpse of the geologic insight that the new technology enabled, we report a few examples of deep geology revealed by this survey in a hydrocarbon- and seismic-data-rich area of the GoM — the Greater Mars-Ursa Basin.

Pre-Stack Full Waveform Inversion for Velocity Model Building

2011 ◽  
Author(s):  
S. Jerry Kapoor ◽  
Denes Vigh ◽  
Timothy John Bunting
Keyword(s):  
Model Building ◽  
Waveform Inversion ◽  
Velocity Model ◽  
Full Waveform Inversion ◽  
Full Waveform ◽  
Velocity Model Building

When Do We Need Elastic Waveform Inversion for Velocity Model Building? Marine and Land Examples

2020 ◽  
Author(s):  
C. Pérez Solano ◽  
G. Chang ◽  
R. Plessix ◽  
K. Bao ◽  
A. Stopin ◽  
...  
Keyword(s):  
Model Building ◽  
Waveform Inversion ◽  
Velocity Model ◽  
Velocity Model Building
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