Shenzi OBN: An imaging step change

2021 ◽  
Vol 40 (5) ◽  
pp. 348-356
Author(s):  
Cheryl Mifflin ◽  
Drew Eddy ◽  
Brad Wray ◽  
Lin Zheng ◽  
Nicolas Chazalnoel ◽  
...  
Keyword(s):  
Model Building ◽  
Seismic Imaging ◽  
Survey Design ◽  
Waveform Inversion ◽  
Complex Salt ◽  
Step Change ◽  
Ocean Bottom ◽  
Maximum Frequency ◽  
Reverse Time ◽  
Time Migration

The story of seismic imaging over BHP's Shenzi Gulf of Mexico production field follows the history of offshore seismic imaging, from 2D to 3D narrow-azimuth streamer acquisition and to its leading the wide-azimuth movement with the Shenzi rich-azimuth (RAZ) survey. Each RAZ reprocessing project over the last 15 years applied the latest processing technology, culminating in hundreds of scenario tests to refine the salt model, but eventually the RAZ data reached a technical limit. A new ocean-bottom-node (OBN) survey acquired in 2020 has produced a step-change improvement over the legacy RAZ image. The uplift can be attributed to several factors. First, an OBN feasibility and survey design study demonstrated that a core of dense nodes combined with sparse nodes would improve the accuracy and resolution of the full-waveform inversion (FWI) solution. Second, the OBN data acquired following the survey design and employing FWI as the main model-building tool realized the predicted improvement. The result was a substantial change to the complex salt model, verified by a salt proximity survey as well as other salt markers, and improvement in imaging over the entire field. In addition to the improvement arising from a more accurate FWI velocity model, the steep-dip imaging also benefited from the new full-azimuth and long-offset data. However, the best steep-dip and fault imaging comes from the FWI image, a direct estimation of reflectivity from the FWI velocity. As the maximum frequency used by FWI moves toward the maximum frequency of the final reverse time migration (RTM), the FWI image approaches the resolution necessary to compete as the primary interpretation volume. Its subsalt illumination surpassed that of the RTM and even the least-squares RTM volumes. These imaging improvements are providing a new understanding of the faults and stratigraphic relationships of the field.

scholarly journals True-amplitude migration through regularized extended linearized waveform inversion

Geophysics ◽  
2021 ◽  
pp. 1-138
Author(s):  
Ettore Biondi ◽  
Mark A. Meadows ◽  
Biondo Biondi
Keyword(s):  
Oil And Gas ◽  
Reservoir Characterization ◽  
Waveform Inversion ◽  
Elastic Behavior ◽  
Ocean Bottom ◽  
Reverse Time ◽  
Image Domain ◽  
Oil And Gas Exploration ◽  
Single Interface ◽  
Time Migration

The ability to create subsurface images whose amplitudes are proportional to the elastic wavefield variations recorded within seismic data as a function of reflection angle is fundamental for performing accurate amplitude-versus-offset (AVO) analysis and inversion. A process that generates such images is commonly referred to as true-amplitude migration. We demonstrate how the extended subsurface-offset image space is able to preserve the elastic behavior of the primary reflections when these events are acoustically migrated with a reverse-time-migration (RTM) approach performed in a least-squares fashion. Using a single-interface model, we show how the angle-domain image amplitude variations from an extended-offset acoustically migrated image closely follow the theoretical elastic Zoeppritz response even at the critical angle. Furthermore, we present a subsalt synthetic test in which single-component ocean-bottom-node (OBN) data are employed within a regularized linearized waveform inversion procedure. In this test, we highlight the ability of the acoustic extended-angle image domain to preserve the correct elastic amplitude variations of the reflected events from three subsalt sand lenses. The proposed method allows the accurate inversion of elastic-wave data for subsurface parameter variations that are critical for reservoir characterization in oil and gas exploration and production. We demonstrate its performance on an ocean-bottom-node (OBN) field dataset recorded in the Gulf of Mexico in which the AVO response of a potential gas-bearing prospect is correctly retrieved.

Subsalt imaging for exploration, production, and development: A review

Geophysics ◽  
2011 ◽  
Vol 76 (5) ◽  
pp. WB3-WB20 ◽  
Author(s):  
Jacques P. Leveille ◽  
Ian F. Jones ◽  
Zheng-Zheng Zhou ◽  
Bin Wang ◽  
Faqi Liu
Keyword(s):  
Model Building ◽  
Special Section ◽  
Low Cost ◽  
Waveform Inversion ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Wide Audience ◽  
Time Migration ◽  
Seismic Acquisition ◽  
Subsalt Imaging

The field of subsalt imaging has evolved rapidly in the last decade, thanks in part to the availability of low cost massive computing infrastructure, and also to the development of new seismic acquisition techniques that try to mitigate the problems caused by the presence of salt. This paper serves as an introduction to the special Geophysics section on Subsalt Imaging for E&P. The purpose of the special section is to bring together practitioners of subsalt imaging in the wider sense, i.e., not only algorithm developers, but also the interpretation community that utilizes the latest technology to carry out subsalt exploration and development. The purpose of the paper is in many ways pedagogical and historical. We address the question of what subsalt imaging is and discuss the physics of the subsalt imaging problem, especially the illumination issue. After a discussion of the problem, we then give a review of the main algorithms that have been developed and implemented within the last decade, namely Kirchhoff and Beam imaging, one-way wavefield extrapolation methods and the full two-way reverse time migration. This review is not meant to be exhaustive, and is qualitative to make it accessible to a wide audience. For each method and algorithm we highlight the benefits and the weaknesses. We then address the imaging conditions that are a fundamental part of each imaging algorithm. While we dive into more technical detail, the section should still be accessible to a wide audience. Gathers of various sorts are introduced and their usage explained. Model building and velocity update strategies and tools are presented next. Finally, the last section shows a few results from specific algorithms. The latest techniques such as waveform inversion or the “dirty salt” techniques will not be covered, as they will be elaborated upon by other authors in the special section. With the massive effort that the industry has devoted to this field, much remains to be done to give interpreters the accurate detailed images of the subsurface that are needed. In that sense the salt is still winning, although the next decade will most likely change this situation.

Seismic acquisition and imaging strategies for unlocking subsurface complexities in Malaysian basins

2020 ◽  
Vol 39 (8) ◽  
pp. 583-590
Author(s):  
Sandeep K. Chandola ◽  
Abdul Aziz Muhamad ◽  
Tang Wai Hoong ◽  
Faizan Akasyah Ghazali ◽  
Ashraf Khalil
Keyword(s):  
Survey Design ◽  
Waveform Inversion ◽  
Integrated Approach ◽  
Seismic Survey ◽  
Reverse Time ◽  
Converted Wave ◽  
Imaging Technologies ◽  
Time Migration ◽  
Seismic Acquisition ◽  
Exploration And Development

Seismic data acquisition and imaging technologies have made important contributions to hydrocarbon discoveries and enhancing recovery from existing reservoirs in Malaysian basins. PETRONAS has been leveraging these technologies to address the exploration and development challenges encountered in Malaysian basins and other parts of the world and to support its play-based exploration. Some of the key technology applications include imaging below shallow gas and carbonates, imaging of complex geology for exploring deep water and deep plays, and high-resolution imaging of shallow clastic plays. Dual and multimeasurement streamers, multiazimuth and full-azimuth seismic, triple- and penta-source blended acquisition, and two- and four-component seabed seismic technologies have been integrated with high-end processing and imaging technologies such as advanced demultiple techniques, deblending, full-waveform inversion, reverse time migration, and PS-converted wave imaging to address complex subsurface challenges. In this article, we present an overview of the evolution and application of innovative seismic acquisition and imaging technologies in Malaysian basins. Selected case histories demonstrate how these technologies have enabled explorers to unlock subsurface complexities, adding value to exploration and development activities. We share the advancements in 3D seismic survey design, marine streamer acquisition, seabed seismic acquisition, and seismic imaging technologies, and how an integrated approach helped PETRONAS address geologic challenges to enhance its exploration success.

Imaging through gas clouds: The application of CSI and FWI in Bohai, China

2021 ◽  
Vol 40 (5) ◽  
pp. 365-373
Author(s):  
Zhengxue Li ◽  
Yong Ma ◽  
Chengbo Li ◽  
Charles C. Mosher ◽  
Jun Ming ◽  
...  
Keyword(s):  
Model Building ◽  
Seismic Imaging ◽  
Oil Field ◽  
Growth Potential ◽  
Bohai Bay ◽  
Ocean Bottom ◽  
Time Migration ◽  
Area 5 ◽  
Seismic Image ◽  
Gas Cloud

Oil field A, situated in Bohai Bay, was discovered in 1999 and has been developed as one of the most productive oil assets in China. It continues to hold significant growth potential for the future. Though the field contains a large amount of resources remaining to be developed, seismic imaging has been challenging in area 5, resulting in structural uncertainty for reservoir interpretation and well planning. In the past three decades, several 2D and 3D seismic surveys have been acquired, processed, and reprocessed in this area. However, due to the existence of complicated gas clouds, which are shallow, multilayered, and extensive, obscured sub-gas-cloud images appear in all legacy seismic results, making fault interpretation under the gas clouds almost impossible. To improve the sub-gas-cloud image and overall structural interpretability, a narrow-azimuth full-field ocean-bottom cable (OBC) acquisition was conducted in field A during 2018 and 2019, and later, a compressive seismic imaging (CSI)-based full-azimuth and large-offset OBC infill survey was acquired in area 5, covering the widest gas cloud. Through high-fidelity signal processing, full-waveform inversion (FWI)-driven velocity model building, and imaging using both Kirchhoff migration and reverse time migration (RTM), the seismic image quality beneath complicated gas clouds is improved significantly. It is the first time that sub-gas-cloud faults and the Base of Guantao event have been imaged by seismic without significant dim zones. CSI acquisition, FWI, and RTM are the key elements to resolve gas-cloud-related challenges in area 5.

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.

scholarly journals Joint migration inversion: features and challenges

2020 ◽  
Vol 17 (3) ◽  
pp. 525-538 ◽  
Author(s):  
Yimin Sun ◽  
Young Seo Kim ◽  
Shan Qu ◽  
Eric Verschuur
Keyword(s):  
Model Building ◽  
Waveform Inversion ◽  
Solution Space ◽  
Velocity Model ◽  
Synthetic Dataset ◽  
Full Waveform Inversion ◽  
Reverse Time ◽  
Full Waveform ◽  
Time Migration ◽  
Velocity Model Building

Abstract Joint migration inversion is a recently proposed technology, accommodating velocity model building and seismic migration in one integrated process. Different from the widely accepted full waveform inversion technology, it uses imaging parameters, i.e. velocities and reflectivities of the subsurface, to parameterize its solution space. The unique feature of this new technology is its explicit capability to exploit multiples in its inversion scheme, which are treated as noise by most current technologies. In this paper, we comprehensively evaluate the state-of-the-art joint migration inversion technology from various angles: we first benchmark its performance, on both velocity model building and seismic imaging, against that of the well-accepted workflow comprising full waveform inversion and reverse-time migration using a fully controlled 2D realistic synthetic dataset. Next, we demonstrate its application on a 2D field dataset. Last, we use another 2D synthetic dataset to clearly illustrate the challenges the current joint migration inversion technology is facing. With this paper, we transparently reveal the pros of cons of the current joint migration inversion, and we will also point out the imminent research directions joint migration inversion technology should focus on in the next phase for it to be more widely accepted by the geophysics community.

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