Can<i>P</i>-wave AVO be quantitative?

Cambois, Guillaume

doi:10.1190/1.1438516

Cited by 36 publications

(8 citation statements)

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“…There is still controversy about the contribution of gas hydrates at the base of the gas-hydrate stability zone to the observed negative impedance contrast at the BSR (Collett 2001). The accuracy of quantitative results from AVO analysis has not yet been proved (Cambois 2000), and widely used empirical relationships for the elastic moduli of rocks (e.g . Hamilton 1979) are often inappropriate for quantitative studies.…”

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confidence: 99%

AVO study of a gas‐hydrate deposit, offshore Costa Rica

Müller

Bönnemann

Neben

2007

Geophysical Prospecting

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A B S T R A C TAmplitude variation with offset (AVO) analysis and waveform inversion are techniques used to determine qualitative or quantitative information on gas hydrates and free gas in sediments. However, the quantitative contribution of gas hydrates to the acoustic impedance contrast observed at the bottom-simulating reflector and the reliability of quantitative AVO analyses are still topics of discussion. In this study, common-midpoint gathers from multichannel wide-angle reflection seismic data, acquired offshore Costa Rica, have been processed to preserve true amplitude information at the bottom-simulating reflector for a quantitative AVO analysis incorporating angles of incidence of up to 60 • . Corrections were applied for effects that significantly alter the observed amplitudes, such as the source directivity. AVO and rock-physics modelling indicate that free gas immediately beneath the gas-hydrate stability zone can be detected and low concentrations can be quantified from AVO analysis, whereas the offset-dependent reflectivity is not sensitive to gas-hydrate concentrations of less than about 10% at the base of the gas-hydrate stability zone. Bulk free-gas saturations up to 5% have been determined from the reflection seismic data assuming a homogeneous distribution of free gas in the sediment. Assuming a patchy distribution of free gas increases the estimated concentrations up to 14%.There is a patchy occurrence of bottom-simulating reflectors south-east of the Nicoya Peninsula on the continental margin, offshore Costa Rica. AVO analysis indicates that this phenomenon is related to the local presence of free gas beneath the gas-hydrate stability zone, probably related to a focused vertical fluid flow. In areas without bottom-simulating reflectors, the results indicate that no free gas is present.

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confidence: 99%

AVO study of a gas‐hydrate deposit, offshore Costa Rica

Müller

Bönnemann

Neben

2007

Geophysical Prospecting

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“…Hendrickson (1999) notices that AVO crossplot from Auger Field and the crossplot from random noise share similar features, which indicate that the observed background AVO trend can be just noise. Cambois (2000) further finds that noise in the P-wave seismic data may change the form of wavelet variation with offset and bias the estimation of rock properties. Simm et al (2000) find that random noise can be a significant component of noise on AVO crossplots.…”

Section: Introductionmentioning

confidence: 99%

Noise suppression of time migrated gathers using prestack structure oriented filtering

Zhang

Lin

Marfurt

2015

SEG Technical Program Expanded Abstracts 2015

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Prestack seismic analysis provides information on rock properties, lithology, fluid content, and the orientation and intensity of anisotropy. However, such analysis demands high-quality seismic data. Unfortunately, noise is always present in seismic data even after careful processing. Noise in the prestack gathers may not only contaminate the seismic image, thereby lowering the quality of seismic interpretation, but it may also bias the seismic prestack inversion for rock properties, such as acoustic-and shear-impedance estimation. Common postmigration data conditioning includes running window median and Radon filters that are applied to the flattened common reflection point gathers. We have combined filters across the offset and azimuth with edge-preserving filters along the structure to construct a true "5D" filter that preserves amplitude, thereby preconditioning the data for subsequent quantitative analysis. We have evaluated our workflow by applying it to a prestack seismic volume acquired over the Fort Worth Basin, TX. The inverted results from the noise-suppressed prestack gathers are more laterally continuous and have higher correlation with well logs when compared with those inverted from conventional time-migrated gathers.

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“…Recent advances in amplitude variation with offset (AVO) technology have demonstrated that the measurement of conversion of compressional energy to shear energy at interfaces can yield significant information about the fluids and lithology present. Many theoretical, numerical and real data studies carried out during last three decades have witnessed the success of AVO technique (Castagna et al, 1998, Pramanik et al, 2000, Cambois, 2000, Goodway, 2001, Roden et al, 2005. The primary attributes extracted from AVO analysis are the intercepts and the gradients which are obtained from NMO corrected pre-stack amplitudes of conventional P-wave seismic data.…”

Section: Introductionmentioning

confidence: 99%

Impact of phase variations on quantitative AVO analysis: An example from Krishna Godavari Basin, India

Srivastava¹,

Singh²,

Tiwary³

et al. 2006

The Leading Edge

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Effectiveness of AVO techniques has always been a concern for practicing geoscientists in accessing and modelling reservoirs due to wavelet instability in seismic data. In spite of best efforts made during processing, most often, end product is mixed phase seismic data. This paper is an attempt to study the effect of phase in pre-stack seismic data for quantitative AVO analysis to characterise reservoirs for detection, delineation and development. AVO attributes corresponding to known gaseous reservoirs, computed from zero phase seismic show better AVO anomalies. Prior to AVO analysis, to understand AVO classification, petrophysical analysis was carried out for establishing the relation between elastic parameters and also with seismic signatures. AVO modelling has been used to demonstrate the superiority of zero phase seismic data at known gaseous reservoir sands. In absence of source signature, application of well log data for estimation of wavelet present in seismic was made and by dephasing, the mixed phase data was converted to optimum zero phase. In wildcat exploratory areas, explorationists try to establish AVO anomaly using available mixed phase seismic data. It is found that, at times, AVO attributes are not well defined to differentiate AVO anomalies with reference to background trend extracted from this mixed phase data set. In absence of well data, phase rotation of pre-stack gathers at fixed intervals and their analysis is the best possible solution. This has been discussed in detail by applying on a data set at pre-drill stage and confirming the AVO anomaly which has been proved by subsequent drilling. It is also demonstrated that phase rotation is a robust technique and does not generate spurious AVO response, by applying it at known dry well. This approach of analysing well, synthetic and seismic data together for AVO analysis has increased the level of confidence of interpreters for E & P activities related to the gaseous reservoirs.

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CanP-wave AVO be quantitative?

Cited by 36 publications

References 0 publications

AVO study of a gas‐hydrate deposit, offshore Costa Rica

AVO study of a gas‐hydrate deposit, offshore Costa Rica

Noise suppression of time migrated gathers using prestack structure oriented filtering

Impact of phase variations on quantitative AVO analysis: An example from Krishna Godavari Basin, India

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