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ABSTRACT Fundamental and incremental changes in both the technology and methodologies used in imaging are transforming the way we undertake processing and imaging projects. The drivers for this change includes factors internal to the hydrocarbon exploration and production (E&P) industry (for example — the oil price and the increasing commoditization of, particularly, the processing part of projects) and factors driven by the outside world (for example — the pace of computer development, both in hardware and software and the rise of cloud-based systems). In this paper we will look at how the future of seismic imaging is likely to be dominated by the influence of fundamental changes to the way we build models and images of the subsurface and the merging of these two end goals of a traditional imaging project. Amongst the relevant technologies we will discuss are full waveform inversion (FWI) and the goal of high-frequency interpretable models, reflection full waveform inversion and/or reconstructed wavefield inversion (RFWI), Least-squares reverse-time migration (RTM) and the ultimate goal of closed-loop solutions. We illustrate these changes with examples from recent imaging projects in areas of complex geology. Presentation Date: Monday, September 16, 2019 Session Start Time: 1:50 PM Presentation Start Time: 3:55 PM Location: 301B Presentation Type: Oral
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.76)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
High resolution velocity and impedance estimation using refraction and reflection FWI: The Fortuna region, offshore Equatorial Guinea
Jones, Ian F. (ION Geophysical) | Singh, Jeet (ION Geophysical) | Chigbo, Johnny (ION Geophysical) | Cox, Philip (Ophir Energy UK) | Hawke, Colin (Ophir Energy UK) | Harger, Dale (Ophir Energy UK) | Greenwood, Stuart (ION Geophysical)
ABSTRACT The primary objective of this project was to improve the understanding of the internal structure of the Viscata and Fortuna reservoirs, and this objective was met via clearer internal imaging of these reservoir intervals and the overlying gas-charged sediments. The underlying geophysical challenge was the presence of extensive, but small-scale low-velocity gas pockets, which gave rise to significant and cumulative image distortion at target level. This distortion had not been resolved in a vintage 2013 broadband preSDM project, as the velocity model was not sufficiently well resolved. But in the initial commercial phase of this project, high-resolution non-parametric tomography using improved broadband deghosted data enabled us to achieve the stated objectives. The follow-on work, considered here, deals with the use of full waveform inversion, to see if we could further delineate small-scale velocity anomalies, associated with the highly compartmentalized reservoir units, and also, to use the waveform inversion velocities to better constrain and augment acoustic impedance estimation. Presentation Date: Tuesday, September 17, 2019 Session Start Time: 1:50 PM Presentation Time: 3:05 PM Location: 302B Presentation Type: Oral
Abstract Seismic imaging of evaporite bodies is notoriously difficult due to the complex shapes of steeply dipping flanks, adjacent overburden strata, and the usually strong acoustic impedance and velocity contrasts at the sediment-evaporite interface. We consider the geology of salt bodies and the problems and pitfalls associated with their imaging such as complex raypaths, seismic velocity anisotropy, P- and S-wave mode conversions, and reflected refractions. We also review recent developments in seismic acquisition and processing, which have led to significant improvements in image quality and in particular, reverse time migration. We tried to call attention to the form, nature, and consequences of these issues for meaningful interpretation of the resulting images.
- North America > United States (0.46)
- South America > Brazil (0.28)
- Europe > Norway > North Sea (0.28)
- Asia > Middle East (0.28)
- Geology > Rock Type > Sedimentary Rock (1.00)
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline (1.00)
- Geology > Structural Geology > Tectonics > Salt Tectonics (0.98)
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling > Seismic Anisotropy (0.45)
- South America > Brazil > Brazil > South Atlantic Ocean > Santos Basin (0.99)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Ship Shoal South Addition > Block 359 > Mahogany Field (0.99)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Ship Shoal South Addition > Block 349 > Mahogany Field (0.99)
- (4 more...)
Introduction Salt movement often results in steeply-dipping complex structures, which pose significant challenges for model building and migration. In recent years, advances in seismic imaging algorithms have permitted imaging of steep structures by exploiting the two-way wave equation via the introduction of reverse time migration (RTM). With such imaging algorithms, double bounces and turning wave reflections can be imaged, thereby enabling the imaging of vertical and overturned salt flanks. However, despite advances in the migration algorithms, the derivation of a suitable earth model incorporating the anisotropic behaviour of the velocity field remains a significant challenge, requiring tight integration of geological interpretation, and geophysical skills. A major contributing factor to the successful execution of a complex salt imaging project, is the understanding of the many and varied pitfalls involved at every stage of the process. Here we describe and discuss some of these issues.
- Geology > Mineral (0.70)
- Geology > Structural Geology > Tectonics > Salt Tectonics (0.33)
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Ship Shoal South Addition > Block 359 > Mahogany Field (0.99)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Ship Shoal South Addition > Block 349 > Mahogany Field (0.99)
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.
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)
- Overview > Innovation (0.48)
- Instructional Material > Course Syllabus & Notes (0.35)
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)
- North America > United States > Gulf of Mexico > Central GOM > West Gulf Coast Tertiary Basin > Green Canyon > Block 727 > Tonga Field (0.99)
- North America > United States > Gulf of Mexico > Central GOM > West Gulf Coast Tertiary Basin > Green Canyon > Block 727 > Tahiti Field (0.99)
- North America > United States > Gulf of Mexico > Central GOM > West Gulf Coast Tertiary Basin > Green Canyon > Block 727 > Caesar Field (0.99)
- (19 more...)
Resolving Near-Seabed Velocity Anomalies: Deep Water Offshore South East India
Fruehn, Juergen (ION GX Technology) | Jones, Ian F. (ION GX Technology) | Valler, Victoria (ION GX Technology) | Sangvai, Pranaya (Reliance Industries Ltd.) | Mathur, Mohit (Reliance Industries Ltd.) | Biswal, Ajoy (Reliance Industries Ltd.)
Summary Imaging in deep water environments poses a specific set of challenges, both in the data pre-conditioning and the velocity model building. These challenges include scattered complex 3D multiples, aliased noise, and low velocity shallow anomalies associated with channel fills and gas hydrates. In this paper, we describe an approach to tackling such problems for data from deep water off the north east coast of India, concentrating our attention on iterative velocity model building, more specifically the resolution of near surface and other velocity anomalies. In the region under investigation, the velocity field is complicated by narrow buried canyons (500 m wide) filled with low velocity sediments which give rise to severe pull-down effects; possible free gas accumulation below an extensive gas hydrate cap, producing dimming of the image below (perhaps as a result of absorption); and thin channel bodies with low-velocity fill. Hybrid gridded tomography using a conjugate gradient solver (with 20 m vertical cell size) is used to resolve small scale velocity anomalies (with thicknesses of about 50m). Manual picking of narrow channel features is used to define bodies too small for the tomography to resolve. Pre-stack depth migration using a velocity model built using a combination of these techniques was able to resolve pull-down and other image distortion effects in the final image. The resulting velocity field shows high resolution detail useful in identifying anomalous geobodies of potential exploration interest. Introduction Off the east coast of India, the transition from the shallower coastal waters to the deep shelf often encounters significant topographical variation in the sea bed, which gives rise to numerous effects which must be dealt with by the processing geophysicist. In addition to deep channels and steep slopes, we also encounter buried channels with low velocity fills and gas hydrates. Diffracted and "out-ofplane" multiples are the norm in these environments (Stewart, 2004), and must be dealt with in order to subsequently derive a reliable velocity model so as to deliver an acceptable structural image (Stewart et al, 2007). In the data considered here, the water depths range from a few hundred metres to over 1 km, and for the most part are deeper than 1.5 km, with deeply incised sea-bed channels running down the continental slope. The region under consideration is roughly 42 km by 54 km (some 2200 sq.km) covering a large exploration area of unknown hydrocarbon potential. The data were collected in 2004, and imaged after 2D demultiple using 3D pre-stack time migration (preSTM). This time domain imaging produced very good results overall, but for certain specific parts of the region was considered sub-optimal. The areas where time migration constitutes an inadequate imaging solution are those areas affected by significant ray bending; such as directly below steep sided sea-floor canyons, or beneath low velocity geobody lenses. As with any complex or subtle imaging problem, the key to good imaging is the derivation of a representative velocity model. In order to obtain such a model, we must first produce clean multiple-free pre-stack data.
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)
Complex Imaging Challenges: Offshore South East India.
Sangva, Pranaya (Reliance Industries Ltd.) | Biswal, Ajoy (Reliance Industries Ltd.) | Mathur, Mohit (Reliance Industries Ltd.) | Fruehn, Juergen (ION GX Technology) | Smith, Phil (ION GX Technology) | Jones, Ian F. (ION GX Technology) | King, Dave (ION GX Technology) | Goodwin, Mike (ION GX Technology) | Valler, Victoria (ION GX Technology)
Summary Imaging in deep water environments poses a specific set of challenges, both in the data pre-conditioning and the imaging. These challenges include scattered complex 3D multiples, aliased noise; and low velocity shallow anomalies associated with channel fills and gas hydrates. In this paper, we describe our approach to tackling these problems, concentrating our attention on multiple suppression, scattered noise attenuation, iterative velocity model building and depth imaging. Deep Water Issues Off the east coast of India, the transition from the shallower coastal waters to the deep shelf often encounters significant topographical variation in the sea bed, which gives rise to numerous effects which must be dealt with by the processing geophysicist. In addition to deep channels and steep slopes, we also encounter buried channels with low velocity fills and gas hydrates. Diffracted and “out-ofplane” multiples are the norm in these environments (Stewart, 2004), and must be dealt with in order to subsequently derive a reliable velocity model in order to deliver an acceptable structural image (Stewart et al, 2006). To address multiples, differential velocity based methods such as Parabolic Radon have often been used in deep water. To some extent, the problem of aliasing of the multiples on far offsets can be addressed either by interpolation and/or use of a de-aliased (‘beam’) Radon transform. However, Radon-based techniques fail for complex multiples, as the apex of the events in the CMP domain does not fall on zero offset for ray paths not in the plane of the shot-receiver axis. In these cases, an alternative method must be employed. In recent years, the SRME technique has become popular in deep water. Near offset multiples in particular are better attenuated than with Parabolic Radon technique. Cascading 2D SRME and Radon has become an industry standard approach. However, the complexity of the multiple generator and “out-of-plane” effects can severely limit even this combination. With the advent of 3D SRME, a theoretically more correct approach has become available, and here we demonstrate its effectiveness as compared to the ‘conventional’ approach. In figure 1, we show data sorted to CMP gathers after application of the SRME technique (which is applied to shot gathers). We compare results from 2D SRME with those from 3D SRME. Complex ray-paths for the first seabed multiple and associated sedimentary layers, give-rise to a shifted-apex aspect to the moveout behaviour as seen in the CMP domain. Following either 2D or 3D SRME, additional de-noise techniques can be applied to deal with the aliased noise and other classes of noise. Velocity Model Building & Pre-Stack Depth Migration In an environment with punctual discontinuous velocity anomalies, such as those associated with narrow channel fills or gas hydrate accumulations, a purely layer based velocity model will be inadequate (Jones, 2003). Furthermore, a purely gridded approach may also encounter problems (Jones, et al, 2007). In this project (Sangvai et al, 2008), we used a hybridgridded approach, where we combined conventional gridded tomography, high resolution gridded tomography, auto-picked layers, and detailed manually interpreted layers.
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)
Much of the thinking behind conventional geophysical processing assumes that we wanted to image energy that propagates down from the surface of the earth, scatters from a reflector or diffractor, and then propagates back up to the recording surface without being reflected by any other feature. Such travel paths conform to the assumptions of one-way wave propagation, and most contemporary migration schemes are designed to image such data. In addition, the moveout behavior of these primary reflection events in the various prestack domains is well understood, and many of our standard data-preprocessing techniques relied on the assumption that this behavior adequately describes the events we wanted to preserve for imaging. As a corollary, events that do not conform to this prescribed behavior are classified as noise, and many of our standard preprocessing techniqueswere designed to remove them. We assessed the kinematics of moveout behavior of events that arise from two-way wave propagation and the effect of certain preprocessing techniques on those events. This was of interest to us because the recent rapid increase in available cost-effective computing power has enabled industrial implementation of migration algorithms—particularly reverse-time migration—that in principle can image events that reflect more than once on their way from source to receiver. We used 2D synthetic data to show that some conventional data-processing steps—particularly those used in suppression of complex reverberations (“multiples”)—remove nonreverberatory primary events from seismic reflection data. Specifically, they remove events that have repeated or turning reflections in the subsurface (such as double-bounce arrivals) but that otherwise are imageable using reverse-time migration.
Imaging in deep-water environments poses a specific set of challenges, both in data preconditioning and velocity model building. These challenges include scattered, complex 3D multiples, aliased noise, and low-velocity shallow anomalies associated with channel fills and gas hydrates. We describe an approach to tackling such problems for data from deep water off the east coast of India, concentrating our attention on iterative velocity model building, and more specifically the resolution of near-surface and other velocity anomalies. In the region under investigation, the velocity field is complicated by narrow buried canyons ( wide) filled with low-velocity sediments, which give rise to severe pull-down effects; possible free-gas accumulation below an extensive gas-hydrate cap, causing dimming of the image below (perhaps as a result of absorption); and thin-channel bodies with low-velocity fill. Hybrid gridded tomography using a conjugate gradient solver (with vertical cell size) was applied to resolve small-scale velocity anomalies (with thicknesses of about ). Manual picking of narrow-channel features was used to define bodies too small for the tomography to resolve. Prestack depth migration, using a velocity model built with a combination of these techniques, could resolve pull-down and other image distortion effects in the final image. The resulting velocity field shows high-resolution detail useful in identifying anomalous geobodies of potential exploration interest.
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)