Applications of spectral decomposition for AVO analyses in the west of Shetland

Abstract

In this paper we have compared the AVO analyses from four wells in the west of Shetland: Foinaven oil well (204/24A-2); Laggan gas well (206/1-2) and two prospect wells (204/17-1 and Assynt 204/18-1). We apply the spectral decomposition to the data from these four wells and provide further evidence that there are also differences in the spectral characteristics between the four wells. While Foinaven and Laggan Class III AVO anomalies are consistent theoretical predictions for frequency-dependent AVO behaviours. However, the results from the Assynt prospect 204/18-1 and another prospect 204/17-1 show rather complicated behaviour in the iso-frequency sections that cannot be fully explained. In summary, though the amplitude anomalies seen in the two prospects were originally interpreted as to be similar to the Foinaven, but our study indicated they are different in both the AVO behaviour and the spectral characteristics.

An Improved Method for the Modeling of Frequency-Dependent Amplitude-Versus-Offset Variations

“…1(b) significantly alters the feature of frequencydependent AVO responses. The stacked amplitudes show an increase and then a decrease with frequency, which implies that the presence of the layered structure may provide an interpretation for the observations in the work of Liu et al [16]. In addition, AVO responses at low-and high-frequency limits in Fig.…”

“…In the work of Liu et al [16], similar type III AVO responses and decreasing amplitudes for increasing frequency were observed in the iso-frequency sections, and were interpreted as the presence of hydrocarbons. In another case of the same work, however, the authors found that the stacked amplitudes show more complicated variations, changing dramatically from an increase to a decrease with frequency.…”

“…Therefore, proper descriptions of frequency-dependent AVO responses should incorporate the effects of both layered structure of a reservoir and dispersive and attenuated properties of media in the reservoir. Current researches on frequencydependent AVO are mainly based on White's patchy-saturation model [1] and Chapman's squirt-flow model [2], [3], and take assumptions of either normal-incident reflection [10], [11] or interface reflection model [12]- [14], and have not accurately considered dispersion and attenuation by truncating imaginary parts of complex stiffnesses predicted by rock physics models in the calculation of frequency-dependent reflection coefficients [15], [16].…”

Modeling and Analysis of Frequency‐Dependent AVO Responses in Anelastic Stratified Media

“…Current studies usually use conventional Zoeppritz equations that are based on the single interface model while have not considered the E-mail: guozhiqi@jlu.edu.cn effects of layered structures. Liu et al (2006) found that seismic reflections from oil-and gas-bearing reservoirs do not show the abnormal high amplitude at low-frequency. This may be due to tuning and interferences of the bandwidth-limited seismic reflections that lead to the frequency-dependency of the complicated waveforms (Gao et al, 2003(Gao et al, , 2006Li et al, 2012Li et al, , 2013.…”

“…According to these rock physics models, , Chapman et al ( , 2006 and Liu et al (2006) researched the applications of the frequency-dependent AVO on reservoir fluid identification. Quintal et al (2007), Ren et al (2009aRen et al ( , 2009b and Teng et al (2013) classified frequency-dependent AVO based on forward modeling and the White model.…”