Case study: The importance of gas leakage in interpreting amplitude‐versus‐offset (AVO) analysis

1989 ◽  
Author(s):  
M. K. Sengupta ◽  
C. A. Rendleman
Keyword(s):  
Avo Analysis ◽  
Gas Leakage ◽  
Amplitude Versus Offset ◽  
Amplitude Versus

Case study: The importance of gas leakage in interpreting amplitude‐versus‐offset (AVO) analysis

Geophysics ◽  
1991 ◽  
Vol 56 (11) ◽  
pp. 1886-1895 ◽  
Author(s):  
M. K. Sengupta ◽  
C. A. Rendleman
Keyword(s):  
Seismic Energy ◽  
Gas Content ◽  
Bright Spot ◽  
Seismic Section ◽  
Gas Leakage ◽  
Hydrocarbon Reservoir ◽  
Reflection Amplitude ◽  
Amplitude Versus Offset ◽  
Amplitude Anomaly ◽  
Amplitude Versus

The amplitude‐versus‐offset (AVO) method has been shown to indicate the presence of gas sands if the reflection amplitude from the seal/reservoir‐sand interface, measured in a common midpoint (CMP) gather, increases rapidly with increasing shot‐to‐geophone distance (or offset). However, in a few instances, it has been observed that the seismic reflection amplitude does not increase with offset and may even decrease if there is widespread gas leakage above the hydrocarbon reservoir causing partial gas saturation in the overburden sediments. Gas‐charged sediments are known to attenuate seismic energy. Depending on the size and shape of this gas leakage zone, there may be higher attenuation of seismic amplitudes with increasing offset. We present one such case that involves a prominent “bright‐spot” amplitude anomaly corresponding to a 56‐ft‐thick (17 m‐thick) gas sand in the Gulf of Mexico slope. The reflection amplitude for the sand top was found to decrease with increasing offset. There is also evidence of gas leakage into the sediments above the reservoir. Color amplitude displays of the seismic section show a low‐amplitude diffused zone above the bright‐spot amplitude anomaly, which suggests gas leakage. Further evidence of gas leakage can be inferred from the significant gas content (including heavier hydrocarbons) observed in the mud log. Gas leakage is also confirmed by gather modeling in which the effects of leakage‐caused attenuation are accounted for in matching the variation of seismic amplitude with offset.

Amplitude preservation of Radon-based multiple-removal filters

Geophysics ◽  
2006 ◽  
Vol 71 (5) ◽  
pp. V123-V126 ◽  
Author(s):  
Ethan J. Nowak ◽  
Matthias G. Imhof
Keyword(s):  
Radon Transform ◽  
Seismic Data ◽  
Transform Domain ◽  
Multiple Reflections ◽  
Avo Analysis ◽  
Amplitude Versus Offset ◽  
Amplitude Preservation ◽  
Amplitude Versus

This study examines the effect of filtering in the Radon transform domain on reflection amplitudes. Radon filters are often used for removal of multiple reflections from normal moveout-corrected seismic data. The unweighted solution to the Radon transform reduces reflection amplitudes at both near and far offsets due to a truncation effect. However, the weighted solutions to the transform produce localized events in the transform domain, which minimizes this truncation effect. Synthetic examples suggest that filters designed in the Radon domain based on a weighted solution to the linear, parabolic, or hyperbolic transforms preserve the near- and far-offset reflection amplitudes while removing the multiples; whereas the unweighted solutions diminish reflection amplitudes which may distort subsequent amplitude-versus-offset (AVO) analysis.

scholarly journals An integrated petrophysical-based wedge modeling and thin bed AVO analysis for improved reservoir characterization of Zhujiang Formation, Huizhou sub-basin, China: A case study

2020 ◽  
Vol 12 (1) ◽  
pp. 256-274
Author(s):  
Wasif Saeed ◽  
Hongbing Zhang ◽  
Qiang Guo ◽  
Aamir Ali ◽  
Tahir Azeem ◽  
...  
Keyword(s):  
Seismic Data ◽  
Reservoir Characterization ◽  
Dominant Frequency ◽  
Well Logs ◽  
Amplitude Versus Offset ◽  
Avo Attributes ◽  
Thin Reservoir ◽  
Amplitude Versus

AbstractThe main reservoir in Huizhou sub-basin is Zhujiang Formation of early Miocene age. The petrophysical analysis shows that the Zhujiang Formation contains thin carbonate intervals, which have good hydrocarbon potential. However, the accurate interpretation of thin carbonate intervals is always challenging as conventional seismic interpretation techniques do not provide much success in such cases. In this study, well logs, three-layer forward amplitude versus offset (AVO) model and the wedge model are integrated to analyze the effect of tuning thickness on AVO responses. It is observed that zones having a thickness greater than or equal to 15 m can be delineated with seismic data having a dominant frequency of more than 45 Hz. The results are also successfully verified by analyzing AVO attributes, i.e., intercept and gradient. The study will be helpful to enhance the characterization of thin reservoir intervals and minimize the risk of exploration in the Huizhou sub-basin, China.

Thin‐bed AVO: Compensating for the effects of NMO on reflectivity sequences

Geophysics ◽  
2001 ◽  
Vol 66 (6) ◽  
pp. 1714-1720 ◽  
Author(s):  
Alessandro Castoro ◽  
Roy E. White ◽  
Rhodri D. Thomas
Keyword(s):  
Normal Incidence ◽  
Wavelet Estimation ◽  
Avo Analysis ◽  
Seismic Wavelet ◽  
Amplitude Versus Offset ◽  
Nmo Correction ◽  
Fourier Spectra ◽  
Nmo Stretch ◽  
Amplitude Versus

Estimating the amplitude versus offset (AVO) gradient for thin beds is problematic because of offset‐dependent tuning and NMO stretch. When AVO analysis is carried out before NMO correction, the nonparallel nature of the NMO hyperbolas results in differential interference conditions at each offset and complicates AVO interpretation. If AVO analysis is carried out after NMO correction, the data bandwidth is distorted and corrections must be made to recover the true AVO response. A correction for NMO stretch can be applied to Fourier spectra obtained after windowing the NMO‐corrected prestack data. This approach requires knowledge of the seismic wavelet but seems to be relatively insensitive to noise in the data or uncertainties in the wavelet estimation. The technique allows the interference conditions to be made independent of offset and the correct AVO gradient relative to the normal incidence amplitude to be recovered.

scholarly journals Identification of Sandstone Reservoir Saturated by Oil Using Low Frequency Analysis with base on CWT and AVO Analysis

2016 ◽  
Vol 4 (01) ◽  
pp. 55
Author(s):  
Sudarmaji S ◽  
Budi Eka Nurcahya
Keyword(s):  
Wavelet Transform ◽  
Frequency Analysis ◽  
Low Frequency ◽  
Class Iii ◽  
Porous Rock ◽  
Avo Analysis ◽  
Reflection Seismic ◽  
Amplitude Versus Offset ◽  
Sandstone Reservoir ◽  
Amplitude Versus

<span>Identification of sandstone resevoir saturated by oil has been conducted by mean low <span>frequency and amplitude versus offset (AVO) analysis. Low Frequency analysis was has been <span>conducted among 3D and 2D seismic data of PSTM gather using continuose wavelet transform <span>(CWT) around 15hz. Low frequency analysis was done by calculating attribute gradient time <span>frequency of instantaneous amplitude using continuous wavelet transform (CWT) around <span>15hz for detecting the existing diffusive wave from reflection seismic. Diffusive wave is a <span>wave that appears due to fluid movement in porous rock, especially fluid of hydrocarbon with <span>certain viscosity and permeability. While amplitude versus offset (AVO) analysis was done <span>for detecting the impedance character of sandstone reservoir that related to porous rock. <span>Amplitude versus offset (AVO) analysis was done by calculating gradient*intercept and <span>observing the curve of wave reflectivity as a function of offset. The positive value of <span>gradient*intercept and curve of reflectivity as a function of offset could be identified as AVO<br /><span>class III and correlated to sandstone reservoir with low impedance and good porosity.</span></span></span></span></span></span></span></span></span></span></span></span><br /></span>

scholarly journals AVO analysis aids in differentiation between false and true amplitude responses: a case study of El Mansoura field, onshore Nile Delta, Egypt

2019 ◽  
Vol 10 (3) ◽  
pp. 969-989 ◽  
Author(s):  
Mohamed Hussein ◽  
Ahmed Abu El-Ata ◽  
Mohamed El-Behiry
Keyword(s):  
Nile Delta ◽  
Gas Reservoirs ◽  
Amplitude Response ◽  
Avo Analysis ◽  
Amplitude Versus Offset ◽  
Amplitude Anomaly ◽  
Dry Sand ◽  
Exploratory Wells ◽  
The Impact

AbstractThe seismic amplitude versus offset (AVO) analysis has become a prominent in the direct hydrocarbon indicator in last decade, aimed to characterizing the fluid content or the lithology of a possible reservoir and reducing the exploration drilling risk. Our research discusses the impact of studying common depth point gathers on Near, Mid and Far-offsets, to verify the credibility of the amplitude response in the prospect evaluation, through analyzing a case study of two exploratory wells; one has already penetrated a gas-bearing sandstone reservoir and the second one is dry sand, but drilled in two different prospects, using the AVO analysis, to understand the reservoir configuration and its relation to the different amplitude response. The results show that the missing of the short-offset data is the reason of the false anomaly encountered in the dry sand, due to some urban surface obstacles during acquiring the seismic data in the field, especially the study area is located in El Mansoura city, which it is a highly cultivated terrain, with multiple channels and many large orchards on the edge of the river, and sugar cane and rice fields. Several lessons have been learned, which how to differentiate between the gas reservoirs and non-reservoirs, by understanding the relation between the Near and Far-offset traces, to reduce the amplitude anomalies to their right justification, where missing of Near-offset data led to a pseudo-amplitude anomaly. The results led to a high success of exploration ratio as the positives vastly outweigh the negatives.

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