Pitfalls in seismic amplitude versus offset analysis: Case histories

Seismic amplitude anomalies are attractive exploration targets in the Krishna-Godavari Basin offshore India. These bright spots mostly have very high amplitudes, so confident interpretations have been possible. We distinguished between hydrocarbon-bearing sands, water-bearing sands, and high-impedance nonreservoir bodies. Also, we mapped channel architecture and accurately predicted reservoir thickness. Strong amplitude anomalies, prospective seismic character based on an understanding of data phase and polarity, flat spots, and amplitude versus offset have all provided valuable evidence.

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A SEISMIC AMPLITUDE VERSUS OFFSET STUDY IN THE SOLE AREA, GIPPSLAND BASIN

The APPEA Journal ◽

10.1071/aj91020 ◽

1992 ◽

Vol 32 (1) ◽

pp. 265

Author(s):

K.W. Spence ◽

M.W. Ecclestone ◽

I.M. Young

Keyword(s):

Geological Structure ◽

Northern Margin ◽

Seismic Amplitude ◽

The North ◽

Common Depth Point ◽

Amplitude Versus Offset ◽

Main Fault ◽

Significant Extension ◽

Gippsland Basin ◽

Amplitude Versus

Analysis of amplitude versus offset (AVO) variations in shallow reservoirs can be a powerful tool, and has been used to determine the nature and distribution of hydrocarbons in the Sole area.The Sole-1 well was drilled in 1973 on the northern margin of the Gippsland Basin. The well encountered a 16 m dry gas column at the top of the Latrobe Group, within a fault-bounded anticline.Seismic line GS88B-97 was acquired in 1988 over the crest of the Sole Anticline. A dipping reflection event cross-cutting the geological structure was interpreted as a reflection emanating from the base of the gas column. Structural interpretation is ambiguous at the field's northern bounding fault and potential was recognised for a significant extension of the field northwards.An AVO study comparing variations in measured reflection amplitudes on common depth point (CDP) gathers and substacks with modelled results has been successful in unambiguously delineating the field extent and shows that the field is bounded to the north by the main fault. This successful use of AVO techniques at Sole has permitted a more precise estimate of gas in place and has potential for application to other accumulations along the northern margin of the Gippsland Basin.

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Influence of frequency‐dependent anisotropy on seismic amplitude‐versus‐offset signatures for fractured poroelastic rocks

Geophysical Prospecting ◽

10.1111/1365-2478.12981 ◽

2020 ◽

Vol 68 (7) ◽

pp. 2141-2163

Author(s):

Y.‐X. He ◽

S.‐X. Wang ◽

X.‐Y. Wu ◽

B. Xi

Keyword(s):

Frequency Dependent ◽

Seismic Amplitude ◽

Amplitude Versus Offset ◽

Amplitude Versus

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Incomplete AVO near salt structures

Geophysics ◽

10.1190/1.1443268 ◽

1992 ◽

Vol 57 (4) ◽

pp. 543-553 ◽

Cited By ~ 4

Author(s):

Christopher P. Ross

Keyword(s):

Seismic Profiles ◽

Spectral Modeling ◽

Signal Degradation ◽

Amplitude Versus Offset ◽

Bright Spots ◽

Close Proximity ◽

Pseudo Spectral ◽

Amplitude Versus ◽

Structure Class ◽

Made In

Amplitude versus offset (AVO) measurements for deep hydrocarbon‐bearing sands can be compromised when made in close proximity to a shallow salt piercement structure. Anomalous responses are observed, particularly on low acoustic impedance bright spots. CMP data from key seismic profiles traversing the bright spots do not show the expected Class 3 offset responses. On these CMPs, significant decrease of far trace energy is observed. CMP data from other seismic profiles off‐structure do exhibit the Class 3 offset responses, implying that structural complications may be interfering with the offset response. A synthetic AVO gather was generated using well log data, which supports the off‐structure Class 3 responses, further reinforcing the concept of structurally‐biased AVO responses. Acoustic, pseudo‐spectral modeling of the structure substantiates the misleading AVO response. Pseudo‐spectral modeling results suggest that signal degradation observed on the far offsets is caused by wavefield refraction—a shadow zone, where the known hydrocarbon‐bearing sands are not completely illuminated. Such shadow zones obscure the correct AVO response, which may have bearing on exploration and development.

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Research note: Inverse propagation in 1.5‐dimensional amplitude‐versus‐offset joint migration inversion

Geophysical Prospecting ◽

10.1111/1365-2478.13144 ◽

2021 ◽

Author(s):

Yimin Sun ◽

Eric Verschuur

Keyword(s):

Research Note ◽

Amplitude Versus Offset ◽

Inverse Propagation ◽

Amplitude Versus

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QVOA Techniques for Estimation of Fracture Directions

International Journal of Geophysics ◽

10.1155/2018/8592054 ◽

2018 ◽

Vol 2018 ◽

pp. 1-11

Author(s):

Vladimir Sabinin

Keyword(s):

Quality Factor ◽

Symmetry Axis ◽

Factor Versus ◽

Synthetic Data ◽

Computational Techniques ◽

High Quality ◽

Amplitude Versus Offset ◽

Target Layer ◽

Analysis Quality ◽

Amplitude Versus

Some new computational techniques are suggested for estimating symmetry axis azimuth of fractures in the viscoelastic anisotropic target layer in the framework of QVOA analysis (Quality factor Versus Offset and Azimuth). The different QVOA techniques are compared using synthetic viscoelastic surface reflected data with and without noise. I calculated errors for these techniques which depend on different sets of azimuths and intervals of offsets. Superiority of the high-order “enhanced general” and “cubic” techniques is shown. The high-quality QVOA techniques are compared with one of the high-quality AVOA techniques (Amplitude Versus Offset and Azimuth) in the synthetic data with noise and attenuation. Results are comparable.

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