Geologic modeling study of foothill area of the Junggar Basin rim

The varied terrain and complex subsurface structure in the foothill segment of fold and thrust belts results in low-quality seismic data. Therefore, a structural model built only on the basis of seismic will have low reliability and be nonunique. To solve these problems, we have developed a comprehensive modeling method for foothill zones that combines gravity, magnetic (MT), electric, and seismic data. Information from gravity, MT, electric, and seismic data is fully used in each step of modeling. This reduces the nonuniqueness and guarantees the rationality and reliability of the tectonic model. The core of this procedure is simultaneous joint inversing gravity, MT, electric, and seismic multiparameters, which improves the accuracy of velocity model and results in a higher quality of seismic image. The Hala’alate Mountain area in the Junggar Basin, western China, is chosen as the application place, and the process of modeling is evaluated in detail; the structural model is proven to be correct by drilling data. Our method is more accurate and reliable than methods only using seismic data to build a geologic model in foothill zones.

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First-arrival traveltime inversion of seismic diving waves observed on undulant surface

Geophysical Journal International ◽

10.1093/gji/ggab025 ◽

2021 ◽

Vol 225 (2) ◽

pp. 1020-1031

Author(s):

Huachen Yang ◽

Jianzhong Zhang ◽

Kai Ren ◽

Changbo Wang

Keyword(s):

Turning Points ◽

Analytical Formula ◽

Velocity Model ◽

Western China ◽

Inversion Method ◽

Mountain Area ◽

Traveltime Inversion ◽

Static Correction ◽

Velocity Models ◽

First Arrival

SUMMARY A non-iterative first-arrival traveltime inversion method (NFTI) is proposed for building smooth velocity models using seismic diving waves observed on irregular surface. The new ray and traveltime equations of diving waves propagating in smooth media with undulant observation surface are deduced. According to the proposed ray and traveltime equations, an analytical formula for determining the location of the diving-wave turning points is then derived. Taking the influence of rough topography on first-arrival traveltimes into account, the new equations for calculating the velocities at turning points are established. Based on these equations, a method is proposed to construct subsurface velocity models from the observation surface downward to the bottom using the first-arrival traveltimes in common offset gathers. Tests on smooth velocity models with rugged topography verify the validity of the established equations, and the superiority of the proposed NFTI. The limitation of the proposed method is shown by an abruptly-varying velocity model example. Finally, the NFTI is applied to solve the static correction problem of the field seismic data acquired in a mountain area in the western China. The results confirm the effectivity of the proposed NFTI.

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Appraising structural interpretations using seismic data — Theoretical elements

Geophysics ◽

10.1190/geo2018-0128.1 ◽

2019 ◽

Vol 84 (2) ◽

pp. N29-N40

Author(s):

Modeste Irakarama ◽

Paul Cupillard ◽

Guillaume Caumon ◽

Paul Sava ◽

Jonathan Edwards

Keyword(s):

Seismic Data ◽

Structural Model ◽

Synthetic Data ◽

Target Region ◽

Structural Interpretation ◽

Vertical Seismic Profiling ◽

Seismic Image ◽

Vsp Data ◽

Phase Shift Data ◽

Seismic Images

Structural interpretation of seismic images can be highly subjective, especially in complex geologic settings. A single seismic image will often support multiple geologically valid interpretations. However, it is usually difficult to determine which of those interpretations are more likely than others. We have referred to this problem as structural model appraisal. We have developed the use of misfit functions to rank and appraise multiple interpretations of a given seismic image. Given a set of possible interpretations, we compute synthetic data for each structural interpretation, and then we compare these synthetic data against observed seismic data; this allows us to assign a data-misfit value to each structural interpretation. Our aim is to find data-misfit functions that enable a ranking of interpretations. To do so, we formalize the problem of appraising structural interpretations using seismic data and we derive a set of conditions to be satisfied by the data-misfit function for a successful appraisal. We investigate vertical seismic profiling (VSP) and surface seismic configurations. An application of the proposed method to a realistic synthetic model shows promising results for appraising structural interpretations using VSP data, provided that the target region is well-illuminated. However, we find appraising structural interpretations using surface seismic data to be more challenging, mainly due to the difficulty of computing phase-shift data misfits.

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

10.2523/iptc-21771-ms ◽

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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BREATHING NEW LIFE INTO THE EASTERN DAMPIER SUB-BASIN: AN INTEGRATED REVIEW BASED ON GEOPHYSICAL, STRATIGRAPHIC AND BASIN MODELLING EVALUATION

The APPEA Journal ◽

10.1071/aj03004 ◽

2004 ◽

Vol 44 (1) ◽

pp. 123 ◽

Cited By ~ 4

Author(s):

G.P. Thomas ◽

M.R. Lennane ◽

F. Glass ◽

T. Walker ◽

M. Partington ◽

...

Keyword(s):

Seismic Data ◽

Joint Venture ◽

Velocity Model ◽

Upper Jurassic ◽

Source Rocks ◽

Third Order ◽

Geochemical Fingerprinting ◽

Stratigraphic Framework ◽

Seismic Image ◽

Hydrocarbon Charge

The eastern Dampier Sub-basin on Australia’s northwestern margin has been subject to intensive exploration activity since the early 1960s. The commercial success rate for exploration drilling, however, has been a disappointing 8%, despite numerous indications of at least one active petroleum system. During 2002–2003, Woodside and its joint venture partners undertook an integrated review of the area, aimed at unlocking its remaining potential. Stratigraphy, hydrocarbon charge and 3D seismic data quality were addressed in parallel.The eastern Dampier Sub-basin stratigraphy was upgraded from the existing, conventional, second-order tectono-stratigraphic framework to a third-order, exploration-scale, genetic stratigraphic framework. The new framework has regional predictive capability in terms of reservoir (and seal) presence and facies, and has led to recognition of new plays and an enhanced understanding of known plays. One new play involves shoreface sands within the Calypso Formation. New light has been shed on the known Lower Cretaceous M.australis sands play (K30), by the creation of gross depositional environment maps at third-order sequence scale. The Upper Jurassic deepwater clastics play of the Lewis Trough has also been developed, by recognition of four prospective, sand-rich gravity-flow intervals in the early Oxfordian (J42 play).A 3D charge modelling study, underpinned by new geochemical analysis, has allowed delineation of areas of higher and lower risk in terms of hydrocarbon charge and phase (oil versus gas). Key source rocks for oil are identified in the early Oxfordian W.spectabilis biozone, although they are also a likely source for gas in the southwest of the area. The Bathonian-Callovian Upper Legendre Formation is a major source for gas, but could also have contributed minor oil in the northeast of the area. By a combination of geochemical fingerprinting and 3D forward modelling, most hydrocarbon occurrences in the area have been tied to these source intervals, complete with a consistent view of maturities and migration pathways.Some 1,500 km2 of the Panaeus multi-client 3D survey were reprocessed, with close attention to multiple removal, velocities and imaging. A step-change improvement in seismic quality was obtained, together with improved velocities for depth conversion.The prospect portfolio has been polarised and much enhanced through these studies, and the results of several existing wells have become better understood. Some new prospects were identified by apparent direct fluid indications, detected in one case by 3D volume AVO screening. Other new prospects are the result of a clearer seismic image, or of the revised velocity model for depth conversion. New plays are still being followed up, while the fresh light cast on existing plays (e.g. K30 and J42), in combination with improved seismic data, has led to development of several interesting opportunities.

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3D PRE-STACK DEPTH MIGRATION: A TOOL FOR REDUCING EXPLORATION RISK IN THE SWAN GRABEN, TIMOR SEA

The APPEA Journal ◽

10.1071/aj04033 ◽

2005 ◽

Vol 45 (1) ◽

pp. 421

Author(s):

P. Bocca ◽

L. Fava ◽

E. Stolf

Keyword(s):

Seismic Data ◽

Integrated Approach ◽

Velocity Model ◽

Fault Reactivation ◽

Depth Image ◽

Substantial Contribution ◽

Surface Geometry ◽

Depth Migration ◽

Imaging Tool ◽

Seismic Image

3D pre-stack depth migration (PSDM) reprocessing was conducted in 2003 on a portion of the Onnia 3D seismic cube, located in exploration permit AC/P-21, Timor Sea.The main objective of the reprocessing was to obtain the best seismic depth image and the most realistic structural reconstruction of the sub-surface to mitigate the risk factors associated with trap definition (trap retention and trap efficiency). This represents one of the main challenges for oil exploration in the area.The 3D PSDM methodology was chosen as the most appropriate imaging tool to define the correct sub-surface geometry and fault imaging through the use of an appropriate velocity field. An integrated approach to building the final velocity model was adopted, with a substantial contribution from the regional geological model.Several examples are given to demonstrate that the 3D PSDM reprocessing significantly improved the seismic image and thus the confidence in the interpretation, contributing strongly to the definition of the exploration targets.The interpretation of the new seismic data has resulted in a new structural picture in which higher confidence in seismic imaging has improved fault correlation. This has enabled better structural definition at the Middle Jurassic Plover Formation level that has reduced the complexity of the large Vesta Prospect, in the centre of the Swan Graben to the northwest of East Swan–1. Improved understanding of the fault reactivation mechanism and the structural elements of the trap (trap integrity) were eventually incorporated in the prospect risking.In the Swan Graben 3D PSDM has proved to be a very powerful instrument capable of producing significant impact on the exploration even in an area with a complex geological setting and a fairly poor seismic data quality.

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Pitfall experiences when interpreting complex structure with low-quality seismic images

Interpretation ◽

10.1190/int-2014-0118.1 ◽

2015 ◽

Vol 3 (1) ◽

pp. SB29-SB37 ◽

Cited By ~ 1

Author(s):

Bob A. Hardage

Keyword(s):

Seismic Data ◽

Structural Model ◽

Signal To Noise Ratio ◽

Complex Structure ◽

Lessons Learned ◽

Structural Deformation ◽

Structural Interpretation ◽

Seismic Image ◽

Data Volume ◽

Seismic Images

Structural interpretation of seismic data presents numerous opportunities for encountering interpretational pitfalls, particularly when a seismic image does not have an appropriate signal-to-noise ratio (S/N), or when a subsurface structure is unexpectedly complex. When both conditions exist — low S/N data and severe structural deformation — interpretation pitfalls are almost guaranteed. We analyzed an interpretation done 20 years ago that had to deal with poor seismic data quality and extreme distortion of strata. The lessons learned still apply today. Two things helped the interpretation team develop a viable structural model of the prospect. First, existing industry-accepted formation tops assigned to regional wells were rejected and new log interpretations were done to detect evidence of repeated sections and overturned strata. Second, the frequency content of the 3D seismic data volume was restricted to only the first octave of its seismic spectrum to create better evidence of fault geometries. A logical and workable structural interpretation resulted when these two action steps were taken. To the knowledge of our interpretation team, neither of these approaches had been attempted in the area at the time of this work (early 1990s). We found two pitfalls that may be encountered by other interpreters. The first pitfall was the hazard of accepting long-standing, industry-accepted definitions of the positions of formation tops on well logs. This nonquestioning acceptance of certain log signatures as indications of targeted formation tops led to a serious misinterpretation in our study. The second pitfall was the prevailing passion by geophysicists to create seismic data volumes that have the widest possible frequency spectrum. This interpretation effort showed that the opposite strategy was better at this site and for our data conditions; i.e., it was better to filter seismic images so that they contained only the lowest octave of frequencies in the seismic spectrum.

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REFINEMENT OF THE STRUCTURE OF THE VILYUY HEMISYNECLISE BASED ON THE RESULTS OF REINTERPRETATION OF SEISMIC EXPLORATION

GEOLOGY AND MINERAL RESOURCES OF SIBERIA ◽

10.20403/2078-0575-2020-4-40-52 ◽

2020 ◽

pp. 40-52

Author(s):

I. A. Gubin ◽

Keyword(s):

Seismic Data ◽

Structural Model ◽

Rift Zone ◽

Sedimentary Cover ◽

Velocity Model ◽

Seismic Facies ◽

Seismic Exploration ◽

Deep Drilling ◽

Cover Up ◽

Inner Parts

The article analyzes the deep drilling data and results of seismic CDP operations performed within the Vilyuy hemisyneclise from the 1980s to the present. Seismogeological conditions are characterized. The structural model of sedimentary cover up to the top of the Lower Cambrian is developed. 5 seismic sequences are identified, maps of their thicknesses are presented. Proveniances of Mesozoic, Permian, Carboniferous, Devonian, Silurian, Ordovician and Middle-Upper Cambrian deposits are outlined. The structure of the Vilyuy hemisyneclise sedimentary cover is shown on deep seismic-geological sections constructed on the basis of the detailed velocity model, as well as taking into account modern and retrospective geological and geophysical data. The limited development of Devonian deposits in the inner parts of the hemisyneclise is shown, where, according to modern seismic data, the Cambrian is predicted under Carboniferous deposits, and seismic facies characteristic of the Kempendyay rift zone deposits are absent in the wave fields of the pre-Permian part of the section.

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Azimuthally Anisotropic 3D Velocity Continuation

International Journal of Geophysics ◽

10.1155/2011/484653 ◽

2011 ◽

Vol 2011 ◽

pp. 1-8 ◽

Cited By ~ 12

Author(s):

William Burnett ◽

Sergey Fomel

Keyword(s):

Seismic Data ◽

Reservoir Characterization ◽

Azimuthal Velocity ◽

Velocity Model ◽

Seismic Image ◽

Potential Applications ◽

Diffraction Imaging ◽

Principal Directions ◽

Zero Offset ◽

Anisotropic Case

We extend time-domain velocity continuation to the zero-offset 3D azimuthally anisotropic case. Velocity continuation describes how a seismic image changes given a change in migration velocity. This description turns out to be of a wave propagation process, in which images change along a velocity axis. In the anisotropic case, the velocity model is multiparameter. Therefore, anisotropic image propagation is multidimensional. We use a three-parameter slowness model, which is related to azimuthal variations in velocity, as well as their principal directions. This information is useful for fracture and reservoir characterization from seismic data. We provide synthetic diffraction imaging examples to illustrate the concept and potential applications of azimuthal velocity continuation and to analyze the impulse response of the 3D velocity continuation operator.

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Accurate imaging of surface seismic data without a velocity model

10.2523/11523-ms ◽

2007 ◽

Author(s):

Sverre Brandsberg-Dahl ◽

Brian E. Hornby ◽

Xiang Xiao

Keyword(s):

Seismic Data ◽

Velocity Model ◽

Accurate Imaging

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Full-Waveform Inversion for Imaging Faulted Structures: A Case Study from the Japan Trench Forearc Slope

Pure and Applied Geophysics ◽

10.1007/s00024-021-02727-w ◽

2021 ◽

Author(s):

Ehsan Jamali Hondori ◽

Chen Guo ◽

Hitoshi Mikada ◽

Jin-Oh Park

Keyword(s):

Seismic Data ◽

Initial Velocity ◽

Waveform Inversion ◽

Velocity Model ◽

Control Measures ◽

Japan Trench ◽

Full Waveform Inversion ◽

Full Waveform ◽

Time Migration ◽

Shallow Sediments

AbstractFull-waveform inversion (FWI) of limited-offset marine seismic data is a challenging task due to the lack of refracted energy and diving waves from the shallow sediments, which are fundamentally required to update the long-wavelength background velocity model in a tomographic fashion. When these events are absent, a reliable initial velocity model is necessary to ensure that the observed and simulated waveforms kinematically fit within an error of less than half a wavelength to protect the FWI iterative local optimization scheme from cycle skipping. We use a migration-based velocity analysis (MVA) method, including a combination of the layer-stripping approach and iterations of Kirchhoff prestack depth migration (KPSDM), to build an accurate initial velocity model for the FWI application on 2D seismic data with a maximum offset of 5.8 km. The data are acquired in the Japan Trench subduction zone, and we focus on the area where the shallow sediments overlying a highly reflective basement on top of the Cretaceous erosional unconformity are severely faulted and deformed. Despite the limited offsets available in the seismic data, our carefully designed workflow for data preconditioning, initial model building, and waveform inversion provides a velocity model that could improve the depth images down to almost 3.5 km. We present several quality control measures to assess the reliability of the resulting FWI model, including ray path illuminations, sensitivity kernels, reverse time migration (RTM) images, and KPSDM common image gathers. A direct comparison between the FWI and MVA velocity profiles reveals a sharp boundary at the Cretaceous basement interface, a feature that could not be observed in the MVA velocity model. The normal faults caused by the basal erosion of the upper plate in the study area reach the seafloor with evident subsidence of the shallow strata, implying that the faults are active.

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