Effect of VS predictors on amplitude variation with offset response

We have posed a question whether the differences between various [Formula: see text] predictors affect one of the ultimate goals of [Formula: see text] prediction, generating synthetic amplitude variation with offset (AVO) gathers to serve as a calibration tool for interpreting the seismic amplitude for rock properties and conditions. We address this question by evaluating examples in which we test several such predictors at an interface between two elastic layers, at pseudowells, and at a real well with poor-quality S-wave velocity data. The answer based on the examples presented is that no matter which [Formula: see text] predictor is used, the seismic responses at a reservoir are qualitatively identical. The choice of a [Formula: see text] predictor does not affect our ability (or inability) to forecast the presence of hydrocarbons from seismic data. We also find that the amplitude versus angle responses due to different predictors consistently vary along the same pattern, no matter which predictor is used. Because our analysis uses a “by-example” approach, the conclusions are not entirely general. However, the method of comparing the AVO responses due to different [Formula: see text] predictors discussed here is. Hence, in a site-specific situation, we recommend using several relevant predictors to ascertain whether the choice significantly affects the synthetic AVO response and if this response is consistent with veritable seismic data.

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Value of information analysis and Bayesian inversion for closed skew-normal distributions: Applications to seismic amplitude variation with offset data

Geophysics ◽

10.1190/geo2013-0048.1 ◽

2014 ◽

Vol 79 (4) ◽

pp. R151-R163 ◽

Cited By ~ 4

Author(s):

Javad Rezaie ◽

Jo Eidsvik ◽

Tapan Mukerji

Keyword(s):

Seismic Data ◽

Value Of Information ◽

Bayesian Inversion ◽

Information Analysis ◽

Amplitude Variation ◽

Mean Values ◽

Amplitude Variation With Offset ◽

Seismic Amplitude ◽

Value Of Information Analysis ◽

Skew Normal

Information analysis can be used in the context of reservoir decisions under uncertainty to evaluate whether additional data (e.g., seismic data) are likely to be useful in impacting the decision. Such evaluation of geophysical information sources depends on input modeling assumptions. We studied results for Bayesian inversion and value of information analysis when the input distributions are skewed and non-Gaussian. Reservoir parameters and seismic amplitudes are often skewed and using models that capture the skewness of distributions, the input assumptions are less restrictive and the results are more reliable. We examined the general methodology for value of information analysis using closed skew normal (SN) distributions. As an example, we found a numerical case with porosity and saturation as reservoir variables and computed the value of information for seismic amplitude variation with offset intercept and gradient, all modeled with closed SN distributions. Sensitivity of the value of information analysis to skewness, mean values, accuracy, and correlation parameters is performed. Simulation results showed that fewer degrees of freedom in the reservoir model results in higher value of information, and seismic data are less valuable when seismic measurements are spatially correlated. In our test, the value of information was approximately eight times larger for a spatial-dependent reservoir variable compared with the independent case.

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AVO analysis for high amplitude anomalies using 2D pre-stack seismic data

Kuwait Journal of Science ◽

10.48129/kjs.12351 ◽

2022 ◽

Author(s):

Lamees N. Abdulkareem ◽

Keyword(s):

Seismic Data ◽

High Amplitude ◽

Rock Properties ◽

Fluid Substitution ◽

Amplitude Variation ◽

Amplitude Variation With Offset ◽

The Real ◽

North West ◽

Avo Analysis ◽

Controlling Parameter

Amplitude variation with offset (AVO) analysis is an 1 efficient tool for hydrocarbon detection and identification of elastic rock properties and fluid types. It has been applied in the present study using reprocessed pre-stack 2D seismic data (1992, Caulerpa) from north-west of the Bonaparte Basin, Australia. The AVO response along the 2D pre-stack seismic data in the Laminaria High NW shelf of Australia was also investigated. Three hypotheses were suggested to investigate the AVO behaviour of the amplitude anomalies in which three different factors; fluid substitution, porosity and thickness (Wedge model) were tested. The AVO models with the synthetic gathers were analysed using log information to find which of these is the controlling parameter on the AVO analysis. AVO cross plots from the real pre-stack seismic data reveal AVO class IV (showing a negative intercept decreasing with offset). This result matches our modelled result of fluid substitution for the seismic synthetics. It is concluded that fluid substitution is the controlling parameter on the AVO analysis and therefore, the high amplitude anomaly on the seabed and the target horizon 9 is the result of changing the fluid content and the lithology along the target horizons. While changing the porosity has little effect on the amplitude variation with offset within the AVO cross plot. Finally, results from the wedge models show that a small change of thickness causes a change in the amplitude; however, this change in thickness gives a different AVO characteristic and a mismatch with the AVO result of the real 2D pre-stack seismic data. Therefore, a constant thin layer with changing fluids is more likely to be the cause of the high amplitude anomalies.

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Amplitude components analysis: Theory and application

The Leading Edge ◽

10.1190/tle39010062a1.1 ◽

2020 ◽

Vol 39 (1) ◽

pp. 62a1-62a6 ◽

Cited By ~ 1

Author(s):

Mohammed Farfour

Keyword(s):

Seismic Data ◽

Spectral Decomposition ◽

Poor Quality ◽

Seismic Signals ◽

Amplitude Variation ◽

Amplitude Variation With Offset ◽

Reservoir Rocks ◽

Analysis Theory ◽

Components Analysis ◽

Carbonate Formations

Seismic data are rich in information about subsurface formations and their pore content. This information can be retrieved from the amplitude or frequencies of seismic signals. Spectral decomposition is a seismic interpretation technique that enables interpreters to decompose the broadband of seismic signals into constituent frequencies. Likewise, amplitude components analysis (ACA) is an approach proposed to compute amplitude constituent components as a function of offset. The approach uses amplitude-variation-with-offset approximations to extract amplitude components that compose the amplitudes in stacked sections. ACA can be used to screen seismic data for possible hidden anomalies that may be associated with hydrocarbons. ACA also helps predict seismic responses at angles where data are not recorded or are of poor quality. Because abnormal expressions associated with hydrocarbons can be observed in clastic and carbonate formations, the approach can look for the expressions in both types of reservoir rocks.

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Amplitude components analysis: Theory and application

The Leading Edge ◽

10.1190/tle39010062.1 ◽

2020 ◽

Vol 39 (1) ◽

pp. 62a1-62a6

Author(s):

Mohammed Farfour

Keyword(s):

Seismic Data ◽

Spectral Decomposition ◽

Poor Quality ◽

Seismic Signals ◽

Amplitude Variation ◽

Amplitude Variation With Offset ◽

Reservoir Rocks ◽

Analysis Theory ◽

Components Analysis ◽

Carbonate Formations

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Seismic reservoir characterization of a class-1 amplitude variation with offset turbiditic system located offshore Cote d’Ivoire, West Africa

Interpretation ◽

10.1190/int-2017-0163.1 ◽

2018 ◽

Vol 6 (2) ◽

pp. SD115-SD128

Author(s):

Pedro Alvarez ◽

William Marin ◽

Juan Berrizbeitia ◽

Paola Newton ◽

Michael Barrett ◽

...

Keyword(s):

West Africa ◽

Seismic Data ◽

Reservoir Characterization ◽

Rock Physics ◽

Rock Properties ◽

Well Log ◽

Amplitude Variation ◽

Amplitude Variation With Offset ◽

Fluid Content ◽

Class 1

We have evaluated a case study, in which a class-1 amplitude variation with offset (AVO) turbiditic system located offshore Cote d’Ivoire, West Africa, is characterized in terms of rock properties (lithology, porosity, and fluid content) and stratigraphic elements using well-log and prestack seismic data. The methodology applied involves (1) the conditioning and modeling of well-log data to several plausible geologic scenarios at the prospect location, (2) the conditioning and inversion of prestack seismic data for P- and S-wave impedance estimation, and (3) the quantitative estimation of rock property volumes and their geologic interpretation. The approaches used for the quantitative interpretation of these rock properties were the multiattribute rotation scheme for lithology and porosity characterization and a Bayesian lithofluid facies classification (statistical rock physics) for a probabilistic evaluation of fluid content. The result indicates how the application and integration of these different AVO- and rock-physics-based reservoir characterization workflows help us to understand key geologic stratigraphic elements of the architecture of the turbidite system and its static petrophysical characteristics (e.g., lithology, porosity, and net sand thickness). Furthermore, we found out how to quantify and interpret the risk related to the probability of finding hydrocarbon in a class-1 AVO setting using seismically derived elastic attributes, which are characterized by having a small level of sensitivity to changes in fluid saturation.

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Interpretation of AVO anomalies

Geophysics ◽

10.1190/1.3467825 ◽

2010 ◽

Vol 75 (5) ◽

pp. 75A3-75A13 ◽

Cited By ~ 60

Author(s):

Douglas J. Foster ◽

Robert G. Keys ◽

F. David Lane

Keyword(s):

Wave Velocity ◽

Seismic Data ◽

P Wave ◽

Rock Properties ◽

Light Hydrocarbons ◽

S Wave ◽

Amplitude Variation With Offset ◽

P Wave Velocity ◽

Fluid Properties ◽

Porosity Changes

We investigate the effects of changes in rock and fluid properties on amplitude-variation-with-offset (AVO) responses. In the slope-intercept domain, reflections from wet sands and shales fall on or near a trend that we call the fluid line. Reflections from the top of sands containing gas or light hydrocarbons fall on a trend approximately parallel to the fluid line; reflections from the base of gas sands fall on a parallel trend on the opposing side of the fluid line. The polarity standard of the seismic data dictates whether these reflections from the top of hydrocarbon-bearing sands are below or above the fluid line. Typically, rock properties of sands and shales differ, and therefore reflections from sand/shale interfaces are also displaced from the fluid line. The distance of these trends from the fluid line depends upon the contrast of the ratio of P-wave velocity [Formula: see text] and S-wave velocity [Formula: see text]. This ratio is a function of pore-fluid compressibility and implies that distance from the fluid line increases with increasing compressibility. Reflections from wet sands are closer to the fluid line than hydrocarbon-related reflections. Porosity changes affect acoustic impedance but do not significantly impact the [Formula: see text] contrast. As a result, porosity changes move the AVO response along trends approximately parallel to the fluid line. These observations are useful for interpreting AVO anomalies in terms of fluids, lithology, and porosity.

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Information on elastic parameters obtained from the amplitudes of reflected waves

Geophysics ◽

10.1190/1.1443877 ◽

1995 ◽

Vol 60 (5) ◽

pp. 1426-1436 ◽

Cited By ~ 73

Author(s):

Wojciech Dȩbski ◽

Albert Tarantola

Keyword(s):

Mass Density ◽

Seismic Velocities ◽

Elastic Parameters ◽

Amplitude Variation ◽

Amplitude Variation With Offset ◽

Reflected Waves ◽

Seismic Amplitude ◽

Earth Models ◽

Definition Of ◽

Proper Analysis

Seismic amplitude variation with offset data contain information on the elastic parameters of geological layers. As the general solution of the inverse problem consists of a probability over the space of all possible earth models, we look at the probabilities obtained using amplitude variation with offset (AVO) data for different choices of elastic parameters. A proper analysis of the information in the data requires a nontrivial definition of the probability defining the state of total ignorance on different elastic parameters (seismic velocities, Lamé’s parameters, etc.). We conclude that mass density, seismic impedance, and Poisson’s ratio constitute the best resolved parameter set when inverting seismic amplitude variation with offset data.

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An integrated broadband preprocessing method for towed-streamer seismic data

Geophysics ◽

10.1190/geo2019-0521.1 ◽

2020 ◽

Vol 85 (2) ◽

pp. V201-V221 ◽

Cited By ~ 2

Author(s):

Mehdi Aharchaou ◽

Erik Neumann

Keyword(s):

Seismic Data ◽

High Frequency ◽

Pressure Data ◽

Amplitude Variation ◽

Field Source ◽

Amplitude Variation With Offset ◽

Ringing Artifacts ◽

Joint Application ◽

Amplitude Compensation ◽

Unified Method

Broadband preprocessing has become widely used for marine towed-streamer seismic data. In the standard workflow, far-field source designature, receiver and source-side deghosting, and redatuming to mean sea level are applied in sequence, with amplitude compensation for background [Formula: see text] delayed until the imaging or postmigration stages. Thus, each step is likely to generate its own artifacts, quality checking can be time-consuming, and broadband data are only obtained late in this chained workflow. We have developed a unified method for broadband preprocessing — called integrated broadband preprocessing (IBP) — which enables the joint application of all the above listed steps early in the processing sequence. The amplitude, phase, and amplitude-variation-with-offset fidelity of IBP are demonstrated on pressure data from the shallow, deep, and slanted streamers. The integration allows greater sparsity to emerge in the representation of seismic data, conferring clear benefits over the sequential application. Moreover, time sparsity, full dimensionality, and early amplitude [Formula: see text] compensation all have an impact on broadband data quality, in terms of reduced ringing artifacts, improved wavelet integrity at large crossline angles, and fewer residual high-frequency multiples.

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Application of structural interpretation and simultaneous inversion to reservoir characterization of the Duvernay Formation, Fox Creek, Alberta, Canada

The Leading Edge ◽

10.1190/tle38020151.1 ◽

2019 ◽

Vol 38 (2) ◽

pp. 151-160 ◽

Cited By ~ 6

Author(s):

Ronald Weir ◽

Don Lawton ◽

Laurence Lines ◽

Thomas Eyre ◽

David Eaton

Keyword(s):

Reservoir Characterization ◽

Lateral Displacement ◽

Rock Properties ◽

S Wave ◽

Amplitude Variation With Offset ◽

Structural Interpretation ◽

Simultaneous Inversion ◽

Prestack Inversion ◽

Unconventional Resource ◽

Depth Relationship

Simultaneous prestack inversion of multicomponent 3D seismic data integrated with structural interpretation can provide an effective workflow to maximize value for unconventional plays. We outline an integrated workflow for characterizing the Duvernay play in western Canada, an emerging world-class low-permeability unconventional resource fairway. This workflow includes the determination of a time-depth relationship using synthetic seismograms, generation of seismic-derived time- and depth-converted structural maps, and calculation of inversion-based parameters of density and P- and S-wave velocity. The model-based procedure includes poststack (acoustic) inversion, amplitude variation with offset prestack inversion, and joint PP-PS inversion. With these rock properties determined, calculations are made to determine Young's modulus, Poisson's ratio, and brittleness. Faults are mapped based on time slices, isochrons, and correlatable vertical displacements of stratigraphic marker reflections. Significant strike-slip movements are identified by lateral displacement on interpreted geologic features, such as channels and reef edges. Seismic-derived attributes, combined with structural mapping, highlight zones that are conducive to hydraulic fracturing as well as areas unfavorable for development. Mapping of structural discontinuities provides a framework for understanding zones of preexisting weakness and induced-seismicity hazards.

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Meet West Africa deep exploration challenge with geomorphology and targeted amplitude variation with offset inversion

Interpretation ◽

10.1190/int-2019-0045.1 ◽

2020 ◽

Vol 8 (1) ◽

pp. SA25-SA33

Author(s):

Ellen Xiaoxia Xu ◽

Yu Jin ◽

Sarah Coyle ◽

Dileep Tiwary ◽

Henry Posamentier ◽

...

Keyword(s):

West Africa ◽

Critical Role ◽

Reservoir Quality ◽

Quality Prediction ◽

Reservoir Prediction ◽

Amplitude Variation ◽

Amplitude Variation With Offset ◽

Simultaneous Inversion ◽

Seismic Amplitude ◽

Class 1

Seismic amplitude has played a critical role in the exploration and exploitation of hydrocarbon in West Africa. Class 3 and 2 amplitude variation with offset (AVO) was extensively used as a direct hydrocarbon indicator and reservoir prediction tool in Neogene assets. As exploration advanced to deeper targets with class 1 AVO seismic character, the usage of seismic amplitude for reservoir presence and quality prediction became challenged. To overcome this obstacle, (1) we used seismic geomorphology to infer reservoir presence and precisely target geophysical analysis on reservoir prone intervals, (2) we applied rigorous prestack data preparation to ensure the accuracy and precision of AVO simultaneous inversion for reservoir quality prediction, and (3) we used lateral statistic method to sum up AVO behavior in regions of contrasts to infer reservoir quality changes. We have evaluated a case study in which the use of the above three techniques resulted in confident prediction of reservoir presence and quality. Our results reduced the uncertainty around the biggest risk element in reservoir among the source, charge, and trap mechanism in the prospecting area. This work ultimately made a significant contribution toward a confident resource booking.

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