Time reprocessing and depth imaging of vintage seismic data: the Southern Adriatic Sea case study

2020 ◽  
Author(s):  
Edy Forlin ◽  
Giuseppe Brancatelli ◽  
Nicolò Bertone ◽  
Anna Del Ben ◽  
Riccardo Geletti
Keyword(s):  
Seismic Data ◽  
Model Building ◽  
Adriatic Sea ◽  
Imaging Techniques ◽  
Low Cost ◽  
Velocity Model ◽  
Seismic Section ◽  
P Waves ◽  
Depth Imaging

<p>Nowadays depth imaging of seismic data, using different migration schemes (rays tracing or waves equation methods) and different techniques for velocity model building (i.e. grid or layer-based tomography, isotropic or anisotropic velocity field) is a standard approach for the earth’s subsurface characterization. When dealing with low fold vintage data, acquired with outdated technologies, modern processing algorithms may fail. On the other hand, the reprocessing of these old data with modern techniques may lead to an improvement of quality and resolution, allowing a more accurate interpretation of the investigated geological features. It is important to note that a lot of vintage data were acquired in areas with no recent surveys or currently subject to exploration restrictions. Therefore, available vintage data could be of great importance for all the stakeholders involved in geophysical exploration. We present a case study about the reprocessing of low fold marine seismic data that were acquired in 1971 in the Otranto Channel (Southern Adriatic Sea, Italy).</p><p>The first part of the work consists of a modern broadband sequence processing in the time domain, that allowed us to obtain a pre-stack time migrated seismic section; in the second part, depth imaging has been achieved through a pre-stack depth migration (PSDM). Reliable interval p-waves velocity model has been obtained using two tomographic approaches: grid tomography and layer-based tomography; for both, we carried out several iterations of the refinement loop, consisting of migration, ray tomography, residual velocity analysis, velocity model update.</p><p>The results show significant improvements compared to the original vintage section, in terms of resolution and signal to noise ratio. Moreover, depth imaging and velocity modeling added further information (e.g., reliable interval p-waves velocity model, real geometry and thickness of the main geological units). This study confirms that applying the up-to-date processing and imaging techniques to vintage data, their geophysical and geological value is enhanced and renewed at a relatively low cost.</p>

A case study for azimuthally anisotropic prestack depth imaging of an onshore Alaska prospect

Geophysics ◽  
2010 ◽  
Vol 75 (4) ◽  
pp. B177-B186 ◽  
Author(s):  
Jinming Zhu ◽  
John Mathewson ◽  
Gail Liebelt
Keyword(s):  
Model Building ◽  
Velocity Model ◽  
Image Point ◽  
Depth Imaging ◽  
Depth Migration ◽  
Isotropic Media ◽  
Well Data ◽  
Reflection Tomography ◽  
Very High

In a study of the Sterling-Triangle area of Alaska, U.S.A., we initiated prestack depth migration (PSDM) to improve imaging on a prospect initially identified on a prestack time-migrated (PSTM) volume. Under the isotropic media assumption, the first few iterations of the reflection tomography had difficulty in converging to the proper velocity model. Upon further investigation, a very-high-velocity conglomerate layer was identified in the middle of the section across the whole survey area. We adopted the salt-flood practice, routine in depth-imaging salt provinces such as the Gulf of Mexico. The strategy was to focus on the shallow section above the conglomerate first, followed by a constant-velocity flood for picking the conglomerate base. The finalisotropic PSDM result showed that significant residual moveout differences existed on gathers along different azimuths. The net anisotropic effect on the isotropic PSDM was a degraded final PSDM volume. In the subsequent anisotropic PSDM work, azimuthally variant horizontal velocities were allowed in the model building. Common-image-point (CIP) gathers were created along different azimuths using sectored input gathers. Residuals picked on the sectored CIP gathers were used in joint tomography to invert different horizontal velocities. Incorporating significant well information, we built an anisotropic velocity model such that the azimuthal moveout on the butterfly gathers was essentially flat. The resulting anisotropic PSDM was consistent with well data and could be interpreted with much higher confidence.

Combined pre-stack and post-stack interpretation for velocity model building and hydrocarbon prospectivity: a learning case study from 3D seismic data offshore Gabon

First Break ◽  
2018 ◽  
Vol 36 (12) ◽  
pp. 99-103
Author(s):  
Paolo Esestime ◽  
Milos Cvetkovic ◽  
Jonathan Rogers ◽  
Howard Nicholls ◽  
Karyna Rodriguez
Keyword(s):  
Seismic Data ◽  
Model Building ◽  
Velocity Model ◽  
3D Seismic ◽  
Velocity Model Building ◽  
3D Seismic Data

Separating P‐ and S‐waves in prestack 3D elastic seismograms using divergence and curl

Geophysics ◽  
2004 ◽  
Vol 69 (1) ◽  
pp. 286-297 ◽  
Author(s):  
Robert Sun ◽  
George A. McMechan ◽  
Hsu‐Hong Hsiao ◽  
Jinder Chow
Keyword(s):  
Wave Equation ◽  
Computational Model ◽  
Seismic Data ◽  
Velocity Model ◽  
Scalar Wave ◽  
Elastic Wave Equation ◽  
Seismic Section ◽  
P Waves ◽  
Scalar Wave Equation ◽  
S Waves

The reflected P‐ and S‐waves in a prestack 3D, three‐component elastic seismic section can be separated by taking the divergence and curl during finite‐difference extrapolation. The elastic seismic data are downward extrapolated from the receiver locations into a homogeneous elastic computational model using the 3D elastic wave equation. During downward extrapolation, divergence (a scalar) and curl (a three‐component vector) of the wavefield are computed and recorded independently, at a fixed depth, as a one‐component seismogram and a three‐component seismogram, respectively. The P‐ and S‐velocities in the elastic computational model are then split into two independent models. The divergence seismogram (containing P‐waves only) is then upward extrapolated (using the scalar wave equation) through the P‐velocity model to the original receiver locations at the surface to obtain the separated P‐waves. The x‐component, y‐component, and z‐component seismograms of the curl (containing S‐waves only) are upward extrapolated independently (using the scalar wave equation) through the S‐velocity model to the original receiver locations at the surface to obtain the separated S‐waves. Tests are successful on synthetic seismograms computed for simple laterally heterogeneous 2D models with a 3D recording geometry even if the velocities used in the extrapolations are not accurate.

scholarly journals Crustal-scale depth imaging via joint FWI of OBS data and PSDM of MCS data: a case study from the eastern Nankai Trough

2019 ◽  
Author(s):  
Andrzej Górszczyk ◽  
Stephane Operto ◽  
Laure Schenini ◽  
Yasuhiro Yamada
Keyword(s):  
Seismic Data ◽  
Model Building ◽  
Nankai Trough ◽  
Imaging Techniques ◽  
Velocity Model ◽  
Ocean Bottom ◽  
Structural Factors ◽  
Air Gun ◽  
Imaging Results ◽  
Obs Data

Abstract. Imaging via Pre-Stack Depth Migration (PSDM) from reflection towed-streamer Multi-Channel Seismic (MCS) data at the scale of the whole crust is inherently difficult. This mainly results because the depth-penetration of the seismic wavefield is controlled, firstly (i) by the acquisition design, like streamer length and air-gun source configuration, and secondly (ii) by the complexity of the crustal structure. Indeed, the limited length of the streamer makes the estimation of velocities from deep targets challenging due to the velocity-depth ambiguity. The problem is even more pronounced when processing 2D seismic data, due to the lack of multi-azimuthal coverage. Therefore, in order to broaden our knowledge about the deep crust using seismic methods, one shall target the development of specific imaging workflows integrating different seismic data. Here we propose the combination of velocity model-building using (i) first-arrival traveltime tomography (FAT) and full-waveform inversion (FWI) of wide-angle/long-offset data collected by stationary Ocean Bottom Seismometers (OBS) and (ii) PSDM of short-spread towed-streamer MCS data for reflectivity imaging, using the former velocity model as background model. We present an application of such workflow to seismic data collected by Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and Institut Français de Recherche pour l’Exploitation de la Mer (IFREMER) in the eastern Nankai Trough (Tokai area) during the 2000/2001 SFJ experiment. We show that the FWI model, although derived from OBS data, provides yet an acceptable background velocity field for the PSDM of the MCS data. Furthermore, from the initial PSDM, we first refine the FWI background velocity model by minimizing the residual moveouts (RMO) picked in the prestack migrated volume through slope tomography (ST), from which we generate a better focused migrated image. Such integration of different seismic data sets and leading-edge imaging techniques led to optimal imaging results at different resolution levels. That is, the large-to-intermediate scale crustal units identified in the high-resolution FWI velocity model extensively complement the short-scale reflectivity inferred from the MCS data to better constrain the structural factors controlling the geodynamics of the Nankai Trough area.

Full Wavefield Redatuming: Accurate Velocity Modelling for Imaging Beneath Complex Overburden

2021 ◽  
Author(s):  
Farah Syazana Dzulkefli ◽  
Kefeng Xin ◽  
Ahmad Riza Ghazali ◽  
Guo Qiang ◽  
Tariq Alkhalifah
Keyword(s):  
Wave Propagation ◽  
Seismic Data ◽  
Model Building ◽  
Velocity Model ◽  
Surrounding Rock ◽  
Target Area ◽  
Low Density ◽  
Velocity Model Building ◽  
Seismic Image ◽  
Seismic Wavefield

Abstract Salt is known for having a generally low density and higher velocity compared with the surrounding rock layers which causes the energy to scatter once the seismic wavefield hits the salt body and relatively less energy is transmitted through the salt to the deeper subsurface. As a result, most of imaging approaches are unable to image the base of the salt and the reservoir below the salt. Even the velocity model building such as FWI often fails to illuminate the deeper parts of salt area. In this paper, we show that Full Wavefield Redatuming (FWR) is used to retrieved and enhance the seismic data below the salt area, leading to a better seismic image quality and allowing us to focus on updating the velocity in target area below the salt. However, this redatuming approach requires a good overburden velocity model to retrieved good redatumed data. Thus, by using synthetic SEAM model, our objective is to study on the accuracy of the overburden velocity model required for imaging beneath complex overburden. The results show that the kinematic components of wave propagation are preserved through redatuming even with heavily smoothed overburden velocity model.

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