Integrated gravity and seismic interpretation in the Norman Range, Northwest Territories, Canada

Geophysics ◽  
2007 ◽  
Vol 72 (5) ◽  
pp. B107-B112 ◽  
Author(s):  
Donald C. Lawton ◽  
J. Helen Isaac
Keyword(s):  
Northwest Territories ◽  
Structural Model ◽  
Gravity Data ◽  
Velocity Model ◽  
Data Interpretation ◽  
Deformation Model ◽  
Geologic Mapping ◽  
Seismic Line ◽  
Depth Migration ◽  
Reflection Seismic

We integrate the interpretation of gravity data acquired across the Norman Range near Norman Wells, Northwest Territories, Canada, with geologic mapping and the processing and interpretation of a 2D reflection seismic line. Our purpose is to determine which of two contrasting structural models of deformation is supported by both gravity and seismic data. Interpretation of the gravity data implies that the more likely structural model is that of thin-skinned deformation with a low-angle thrust fault having a décollement within Upper Cambrian evaporites. We use this structural model to guide the development of a velocity model for prestack depth migration of the seismic line. Interpretation of the processed seismic line supports the thin-skinned deformation model.

Rhyl Field: developing a new structural model by integrating basic geological principles with advanced seismic imaging in the Irish Sea

2016 ◽  
Vol 8 (1) ◽  
pp. 355-371 ◽  
Author(s):  
Gavin Ward ◽  
Dean Baker
Keyword(s):  
Structural Model ◽  
Seismic Imaging ◽  
Critical Factor ◽  
Integrated Approach ◽  
Velocity Model ◽  
Irish Sea ◽  
Depth Migration ◽  
Processing Power ◽  
And Migration ◽  
Automated Quality Control

AbstractA new model of compression in the Upper Triassic overlying the Rhyl Field has been developed for the Keys Basin, Irish Sea. This paper highlights the significance of the overburden velocity model in revealing the true structure of the field. The advent of 3D seismic and pre-stack depth migration has improved the interpreter's knowledge of complex velocity fields, such as shallow channels, salt bodies and volcanic intrusions. The huge leaps in processing power and migration algorithms have advanced the understanding of many anomalous features, but at a price: seismic imaging has always been a balance of quality against time and cost. As surveys get bigger and velocity analyses become more automated, quality control of the basic geological assumptions becomes an even more critical factor in the processing of seismic data and in the interpretation of structure. However, without knowledge of both regional and local geology, many features in the subsurface can be processed out of the seismic by relying too heavily on processing algorithms to image the structural model. Regrettably, without an integrated approach, this sometimes results in basic geological principles taking second place to technology and has contributed to hiding the structure of the Rhyl Field until recently.

Tectonic framework of the Barra de São João Graben, Campos Basin, Brazil: Insights from gravity data interpretation

2014 ◽  
Vol 2 (4) ◽  
pp. SJ65-SJ74 ◽  
Author(s):  
Leandro B. Adriano ◽  
Paulo T. L. Menezes ◽  
Alan S. Cunha
Keyword(s):  
Gravity Data ◽  
Shear Zones ◽  
Data Interpretation ◽  
Fault System ◽  
Magnetic Data ◽  
Southeastern Brazil ◽  
Rift System ◽  
Seismic Line ◽  
Structural Framework ◽  
Campos Basin

The Barra de São João Graben (BSJG), shallow water Campos Basin, is part of the Cenozoic rift system that runs parallel to the Brazilian continental margin. This system was formed in an event that caused the reactivation of the main Precambrian shear zones of southeastern Brazil in the Paleocene. We proposed a new structural framework of BSJG based on gravity data interpretation. Magnetic data, one available 2D seismic line, and a density well-log of a nearby well were used as constraints to our interpretation. To estimate the top of the basement structure, we separated the gravity effects of deep sources from the shallow basement (residual anomaly). Then, we performed a 2D modeling exercise, in which we kept fixed the basement topography and the density of the sediments, to estimate the density of the basement rocks. Next, we inverted the residual anomaly to recover the depth to the top of the basement. This interpretation strategy allowed the identification of a complex structural framework with three main fault systems: a northeast–southwest-trending normal fault system, a northwest–southeast-trending transfer fault system, and an east–west-trending transfer fault system. These trends divided the graben into several internal highs and lows. Our interpretation was corroborated by the magnetic anomalies. The existence of ultradense and strongly magnetized elongated bodies in the basement was interpreted as ophiolite bodies that were probably obducted by the time of the shutdown of the Proterozoic Adamastor Ocean.

Practical aspects and applications of 2D stereotomography

Geophysics ◽  
2003 ◽  
Vol 68 (3) ◽  
pp. 1008-1021 ◽  
Author(s):  
Frederic Billette ◽  
Soazig Le Bégat ◽  
Pascal Podvin ◽  
Gilles Lambaré
Keyword(s):  
Estimation Method ◽  
Synthetic Data ◽  
Velocity Model ◽  
Velocity Estimation ◽  
Common Source ◽  
Depth Migration ◽  
Reflection Seismic ◽  
Velocity Models ◽  
Automatic Picking ◽  
Iterative Inversion

Stereotomography is a new velocity estimation method. This tomographic approach aims at retrieving subsurface velocities from prestack seismic data. In addition to traveltimes, the slope of locally coherent events are picked simultaneously in common offset, common source, common receiver, and common midpoint gathers. As the picking is realized on locally coherent events, they do not need to be interpreted in terms of reflection on given interfaces, but may represent diffractions or reflections from anywhere in the image. In the high‐frequency approximation, each one of these events corresponds to a ray trajectory in the subsurface. Stereotomography consists of picking and analyzing these events to update both the associated ray paths and velocity model. In this paper, we describe the implementation of two critical features needed to put stereotomography into practice: an automatic picking tool and a robust multiscale iterative inversion technique. Applications to 2D reflection seismic are presented on synthetic data and on a 2D line extracted from a 3D towed streamer survey shot in West Africa for TotalFinaElf. The examples demonstrate that the method requires only minor human intervention and rapidly converges to a geologically plausible velocity model in these two very different and complex velocity regimes. The quality of the velocity models is verified by prestack depth migration results.

Salt interpretation enabled by reverse-time migration

Geophysics ◽  
2008 ◽  
Vol 73 (5) ◽  
pp. VE211-VE216 ◽  
Author(s):  
Jacobus Buur ◽  
Thomas Kühnel
Keyword(s):  
Model Building ◽  
Velocity Model ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Seismic Line ◽  
Depth Migration ◽  
Time Migration ◽  
Velocity Model Building ◽  
Migration Method

Many production targets in greenfield exploration are found in salt provinces, which have highly complex structures as a result of salt formation over geologic time. Difficult geologic settings, steep dips, and other wave-propagation effects make reverse-time migration (RTM) the migration method of choice, rather than Kirchhoff migration or other (by definition approximate) one-way equation methods. Imaging of the subsurface using any depth-migration algorithm can be done successfully only when the quality of the prior velocity model is sufficient. The (velocity) model-building loop is an iterative procedure for improving the velocity model. This is done by obtaining certain measurements (residual moveout) on image gathers generated during the migration procedure; those measurements then are input into tomographic updating. Commonly RTM is applied around salt bodies, where building the velocity model fails essentially because tomography is ray-trace based. Our idea is to apply RTM directly inside the model-building loop but to do so without using the image gathers. Although the process is costly, we migrate the full frequency content of the data to create a high-quality stack. This enhances the interpretation of top and bottom salt significantly and enables us to include the resulting salt geometry in the velocity model properly. We demonstrate our idea on a 2D West Africa seismic line. After several model-building iterations, the result is a dramatically improved velocity model. With such a good model as input, the final RTM confirms the geometry of the salt bodies and basically the salt interpretation, and yields a compelling image of the subsurface.

A multioffset vertical seismic profiling experiment for anisotropy analysis and depth imaging

Geophysics ◽  
2002 ◽  
Vol 67 (2) ◽  
pp. 348-354 ◽  
Author(s):  
M. Graziella Kirtland Grech ◽  
Don C. Lawton ◽  
Samuel H. Gray
Keyword(s):  
Seismic Velocity ◽  
Velocity Model ◽  
Seismic Profile ◽  
P Wave ◽  
Isotropic Case ◽  
Prestack Depth Migration ◽  
Seismic Line ◽  
Depth Migration ◽  
Velocity Anisotropy ◽  
Anisotropy Parameters

A multioffset vertical seismic profile (VSP) was carried out in the Rocky Mountain foothills of southern Alberta, Canada. The purpose of this experiment was to investigate whether the dipping shale strata exhibit P‐wave velocity anisotropy and, if so, to calculate the Thomsen anisotropy parameters for use in anisotropic depth migration. Traveltime inversion of first‐arrival data from the multioffset VSP revealed that the dipping Mesozoic clastics in the area exhibit seismic velocity anisotropy of about 10%. The anisotropy parameters derived from this experiment were then used in anisotropic prestack depth migration of data from a surface seismic line close to the VSP well. Comparison of the anisotropic migration with the corresponding isotropic prestack depth migration showed that the target was imaged incorrectly in the isotropic case; a lateral shift of 180 m in the updip direction of the overlying beds was observed. The image obtained with an anisotropic velocity model was also better focused than that obtained assuming isotropic velocities.

scholarly journals The marine activities performed within the TOMO-ETNA experiment

2016 ◽  
Vol 59 (4) ◽  
Author(s):  
Mauro Coltelli ◽  
Danilo Cavallaro ◽  
Marco Firetto Carlino ◽  
Luca Cocchi ◽  
Filippo Muccini ◽  
...  
Keyword(s):  
High Resolution ◽  
Structural Model ◽  
Seismic Refraction ◽  
Velocity Model ◽  
Ocean Bottom ◽  
Etna Volcano ◽  
Remotely Operated Vehicle ◽  
Reflection Seismic ◽  
Air Gun ◽  
Mt Etna

<p>The TOMO-ETNA experiment was planned in order to obtain a detailed geological and structural model of the continental and oceanic crust beneath Mt. Etna volcano and northeastern Sicily up to the Aeolian Islands (southern Italy), by integrating data from active and passive refraction and reflection seismic methodologies, magnetic and gravity surveys. This paper focuses on the marine activities performed within the experiment, which have been carried out in the Ionian and Tyrrhenian Seas, during three multidisciplinary oceanographic cruises, involving three research vessels (“Sarmiento de Gamboa”, “Galatea” and “Aegaeo”) belonging to different countries and institutions. During the offshore surveys about 9700 air-gun shots were produced to achieve a high-resolution seismic tomography through the wide-angle seismic refraction method, covering a total of nearly 2650 km of shooting tracks. To register ground motion, 27 ocean bottom seismometers were deployed, extending the inland seismic permanent network of the Istituto Nazionale di Geofisica e Vulcanologia and a temporary network installed for the experiment. A total of 1410 km of multi-channel seismic reflection profiles were acquired to image the subsurface of the area and to achieve a 2D velocity model for each profile. Multibeam sonar and sub bottom profiler data were also collected. Moreover, a total of 2020 km of magnetic and 680 km of gravity track lines were acquired to compile magnetic and gravity anomaly maps offshore Mt. Etna volcano. Here, high-resolution images of the seafloor, as well as sediment and rock samples, were also collected using a remotely operated vehicle.</p>

scholarly journals Advanced Seismic Data Interpretation for Carbonate Targets Based on Optimized Processing Techniques

GeoArabia ◽  
1996 ◽  
Vol 1 (2) ◽  
pp. 285-296
Author(s):  
Klaus C. Fischer ◽  
Ulrich Möller ◽  
Roland Marschall
Keyword(s):  
Seismic Data ◽  
Velocity Model ◽  
Data Interpretation ◽  
Second Phase ◽  
Shelf Area ◽  
Depth Migration ◽  
Amplitude Versus Offset ◽  
And Migration ◽  
Processing Techniques ◽  
Seismic Anomalies

ABSTRACT Seismic data from the shelf area of the Cretaceous Shu’aiba Formation in Abu Dhabi is used to investigate stratigraphic and structural seismic anomalies. The data consists of a 2-D grid of seismic lines, acquired in the late 1980s and 1993. The data was reprocessed in several phases. The first phase consists of standard time domain processing upto final Dip Move Out stack and migration. In the second phase, a macro-velocity model for post-stack depth migration is generated and tested by the interpreters. The third phase is the interpretation of the pre-stack depth migration stack. Due to the structural irregularity of the Shu’aiba Formation, the pre-stack depth migrated data is considered the most reliable for Amplitude Versus Offset analysis. Further steps are L-1 deconvolution followed by Born Inversion. These last steps are required before the lithology can be modeled with high-resolution. The final lithological model is verified by applying forward modeling. The lithological model forms the basis for reservoir and geostatistical evaluations which account for heterogeneities.

New structure maps over the Nuussuaq Basin, central West Greenland

1998 ◽  
pp. 18-27
Author(s):  
James A. Chalmers ◽  
T. Christopher R. Pulvertaft ◽  
Christian Marcussen ◽  
Asger K. Pedersen
Keyword(s):  
Structural Model ◽  
Gravity Data ◽  
Geological Survey ◽  
The South ◽  
Seismic Line ◽  
West Greenland ◽  
Structural Style ◽  
Sea Bed ◽  
Large Step ◽  
Total Lack

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Chalmers, J. A., Pulvertaft, T. C. R., Marcussen, C., & Pedersen, A. K. (1998). New structure maps over the Nuussuaq Basin, central West Greenland. Geology of Greenland Survey Bulletin, 180, 18-27. https://doi.org/10.34194/ggub.v180.5081 _______________ In 1992 the Geological Survey of Greenland (GGU) discovered bitumen in vugs and vesicles in Upper Paleocene basalts in western Nuussuaq (Christiansen et al. 1994). Since then the search for surface oil showings by GGU (from 1995 by the Geological Survey of Denmark and Greenland, GEUS) has resulted in finds over an area extending from northern Disko through Nuussuaq to the south-east corner of Svartenhuk Halvø (Christiansen et al. 1997, 1998, this volume). In addition, slim core drilling by GGU and grønArctic Energy Inc., the holder of an exclusive licence in western Nuussuaq, penetrated oil-saturated rocks at four localities (Christiansen et al. 1996). Encouraged by these results, grønArctic drilled a conventional exploration well (GRO#3) to 2996 m in 1996 (Christiansen et al. 1997), but details about this have not been released. The net effect of these efforts has been to dispel partially the formerly widespread view that the West Greenland area is entirely gas-prone and to promote the Cretaceous– Tertiary Nuussuaq Basin from being a model for what may occur in offshore basins to being a potential petroleum basin in its own right. Evolving conceptions of the Nuussuaq Basin took a large step forward when GGU in 1994 acquired a 13 km 15-fold seismic line on the south coast of Nuussuaq (Christiansen et al. 1995). This showed a sedimentary section 6–8 km thick, much greater than the 2–3 km previously measured from onshore outcrops alone. This showed how little was understood about the structure of the basin, as well as where hydrocarbons might have been generated and where exploration could best be directed. A first step to rectify this situation was taken in 1995 when multichannel seismic and gravity data were acquired by the Survey in Disko Bugt and the fjords north and south of Nuussuaq, as well as west of Disko (Christiansen et al. 1996). The new data have been integrated with older gravity, magnetic and seismic data from both onshore and offshore. This report summarises the results of interpretation of all available geophysical data together with a reappraisal of all available data on faults onshore. Detailed accounts are being published elsewhere (Chalmers 1998; J.A. Chalmers et al. unpublished data). Although the open spacing of the seismic lines and the almost total lack of reflections below the first sea-bed multiple on these lines make it impossible to present a definitive structural model at this stage, the structural style in the basin is now apparent and a number of the major structures in the area have been identified with confidence.

scholarly journals Depth Imaging Sub-salt Structures: A Case Study in the Midyan Peninsula (Red Sea)

GeoArabia ◽  
1999 ◽  
Vol 4 (4) ◽  
pp. 445-464 ◽  
Author(s):  
Denis Mougenot ◽  
Amir A. Al-Shakhis
Keyword(s):  
Red Sea ◽  
Structural Model ◽  
Oil And Gas ◽  
Imaging Techniques ◽  
Depth Image ◽  
Lateral Velocity ◽  
Seismic Line ◽  
Depth Imaging ◽  
Depth Migration ◽  
Velocity Variations

ABSTRACT In the Midyan Peninsula (onshore northern Red Sea, Saudi Arabia), the current prospective oil and gas exploration targets are sub-salt structures. In this region, conventional time-migrated seismic sections are distorted due to the presence of salt diapirs, faults, and related lateral velocity variations. As demonstrated in other sub-salt prospects (North Sea, Gulf of Suez, and Gulf of Mexico), pre-stack depth migration can remove these distortions and accurately focus the structural image. Depth migration, however, requires a model which includes both lateral and vertical velocity variations to compensate for ray bending. Building such a velocity model is an iterative process which involves integration of various time/depth processing and interpretation skills. A 2-D seismic line, crossing various extensional structures in the dip direction, is used to illustrate these depth-imaging techniques. At the location of the sub-salt prospect, the depth image is improved and the lateral position of the main fault is shifted by 345 meters. The resulting structural model has refined the target definition and well position. This imaging approach is compared with the different steps of the seismic processing/interpretation flow.

Kinematic interpretation in the prestack depth‐migrated domain

Geophysics ◽  
1997 ◽  
Vol 62 (4) ◽  
pp. 1226-1237 ◽  
Author(s):  
Irina Apostoiu‐Marin ◽  
Andreas Ehinger
Keyword(s):  
Signal To Noise Ratio ◽  
Velocity Model ◽  
Point Of View ◽  
Prestack Depth Migration ◽  
Depth Migration ◽  
Velocity Models ◽  
Time Domain Data ◽  
And Migration ◽  
Point To Point ◽  
Homogeneous Media

Prestack depth migration can be used in the velocity model estimation process if one succeeds in interpreting depth events obtained with erroneous velocity models. The interpretational difficulty arises from the fact that migration with erroneous velocity does not yield the geologically correct reflector geometries and that individual migrated images suffer from poor signal‐to‐noise ratio. Moreover, migrated events may be of considerable complexity and thus hard to identify. In this paper, we examine the influence of wrong velocity models on the output of prestack depth migration in the case of straight reflector and point diffractor data in homogeneous media. To avoid obscuring migration results by artifacts (“smiles”), we use a geometrical technique for modeling and migration yielding a point‐to‐point map from time‐domain data to depth‐domain data. We discover that strong deformation of migrated events may occur even in situations of simple structures and small velocity errors. From a kinematical point of view, we compare the results of common‐shot and common‐offset migration. and we find that common‐offset migration with erroneous velocity models yields less severe image distortion than common‐shot migration. However, for any kind of migration, it is important to use the entire cube of migrated data to consistently interpret in the prestack depth‐migrated domain.

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