Quantifying uncertainties in attenuation estimation at methane-hydrate-bearing zones using sonic waveform logs

Abstract

Application of seismic attenuation estimation using sonic waveform data is limited because the estimation methods have not yet been fully developed. Although the median frequency shift method is considered to be effective and robust compared to the conventional spectral ratio method, we demonstrated that the median frequency shift methods strongly depend on reference data under lower signal-to-noise ratios. We modified an existing median frequency shift method not to depend on arbitrarily choosing a reference value and to quantify the uncertainties in attenuation estimation. Furthermore, we implied the optimum selection of receiver pairs used for more stable attenuation analysis. Our numerical experiments supported the advantage of the proposed method. Although our main findings by applying the proposed methods in methane hydrate-bearing sediments are almost consistent with past field sonic logging measurements, we find some differences in the magnitude of attenuation values compared to existing sonic attenuation measurements and discuss various possible factors. We believe that more stable and reliable attenuation results can lead to clarifying various factors affecting attenuation estimation, such as the effect of scattering, near-field effects, and source-coupling effects. Furthermore, we emphasized the importance of scattering effect caused by the heterogeneity of the formation and demonstrated the limitation of characterizing the 1D heterogeneity using the sonic logging data spatially sampled at 0.15 m to adequately estimate the effect of scattering attenuation.

Attenuation modes from Vertical Seismic Profiling and sonic waveform in a carbonate reservoir, Abu Dhabi, United Arab Emirates

“…Suzuki and Matsushima () proposed a robust method, which does not depend on an arbitrary choice of the reference value. We used this method to estimate the attenuation from sonic waveforms.…”

“…The intrinsic attenuation indicated a success in oil and gas studies compared with other seismic attributes such as the velocity. Many studies showed that the intrinsic attenuation can be used as an indicator of hydrates and free gas existence, and it allows to obtain information the degree of cementation of gas hydrates (e.g., Guerin and Goldberg ; Matsushima ; Priest, Best, and Clayton ; Shyam and Minshull ; Suzuki and Matsushima ). The intrinsic attenuation can also be used to distinguish gas and condensate from oil and water (e.g.…”

“…To check the repeatability of the results, we applied three methods: two conventional methods, i.e., spectral ratio (Bath ) and centroid frequency shift methods (Quan and Harris ), and a new method based on seismic interferometry (Matsushima, Ali, and Bouchaala ). We estimated the attenuation from monopole and dipole sonic waveforms by applying a method developed for sonic logging waveforms data by Suzuki and Matsushima ().…”

Compensating elastic transmission losses for P‐wave attenuation estimation from sonic logs

“…Since the early 1980s various methods have been developed and applied to determine sonic attenuation from full waveform acoustic logs (Cheng, Toksöz and Willis ; Goldberg, Kan and Castagna ; Dasios, Astin and McCann ; Dasios, McCann and Astin ; Parra, Xu and Hackert ; Qi, Müller and Pervukhina, ). The current view is that the statistical averaging (SA) method yields the most accurate attenuation estimates and is superior to the widely used spectral ratio (SR) method in the presence of noise (Suzuki and Matsushima ). The original SA method for estimating P‐wave attenuation has been developed for sonic logging data acquired in the Ocean Drilling Program (Frazer, Sun and Wilkens ).…”

“…Sun and Frazer () propose yet another method by applying a linear fit with common‐shot gather data to recover the reference attenuation value. Suzuki and Matsushima () modify the SA method so that it does not depend on an arbitrarily chosen reference depth.…”