Quantitative interpretation of waveform attenuation for determining petrophysical properties remains one of the most challenging problems associated with rock physics. In this study, two effective methods are proposed to compute gas saturation in organic-rich shale and tight gas formations from full-waveform sonic attenuations. We first extract compressional (P)- and shear (S)-wave attenuations from monopole and dipole waveforms by median frequency shift and multi-frequency inversion methods, respectively. Crossplots of the P- to S-wave attenuation ratio ($Q_{\mathrm{P}}^{-1}/Q_{\mathrm{S}}^{-1}$) and core gas saturation show a positive linear correlation. The $Q_{\mathrm{P}}^{-1}/Q_{\mathrm{S}}^{-1}$ value and the neutron-density porosity difference exhibit an identical log trend across different formations. The coincidence of these two different hydrocarbon indicators implies that $Q_{\mathrm{P}}^{-1}/Q_{\mathrm{S}}^{-1}$ is most sensitive to pore-fluid saturation and is less affected by variations in lithology. In the first method, the core-calibrated $Q_{\mathrm{P}}^{-1}/Q_{\mathrm{S}}^{-1}$ yields an accurate estimate of gas saturation. The second method is suited for the absence of core saturation data, which use the probability distribution of $Q_{\mathrm{P}}^{-1}/Q_{\mathrm{S}}^{-1}$ for the evaluation of gas saturation. Compared to conventional resistivity methods, the proposed attenuation method, as a nonelectric approach, provides a more accurate gas saturation prediction for low-resistivity reservoir rocks. Finally, we analyze the characteristics of attenuation-saturation relations in low-porosity rocks and discover the possible attenuation mechanisms.

中文翻译：

---

用于量化富含有机物的页岩和致密气层中气体饱和度的衰减方法

用于确定岩石物理特性的波形衰减的定量解释仍然是与岩石物理学相关的最具挑战性的问题之一。在这项研究中，提出了两种有效的方法来从全波形声波衰减计算富含有机物的页岩和致密气层中的气体饱和度。我们首先分别通过中频移频和多频反演方法从单极和偶极波形中提取压缩（P）和剪切（S）波衰减。P波与S波衰减比的交叉图（${问}_{\mathrm{P}}^{-\mathrm{1个}}/{问}_{\mathrm{小号}}^{-\mathrm{1个}}$）与岩心气体饱和度呈正线性相关。的${问}_{\mathrm{P}}^{-\mathrm{1个}}/{问}_{\mathrm{小号}}^{-\mathrm{1个}}$值和中子密度孔隙率差异在不同地层上表现出相同的对数趋势。这两个不同的碳氢化合物指标的巧合意味着${问}_{\mathrm{P}}^{-\mathrm{1个}}/{问}_{\mathrm{小号}}^{-\mathrm{1个}}$对孔隙流体饱和度最敏感，受岩性变化影响较小。在第一种方法中，核心校准${问}_{\mathrm{P}}^{-\mathrm{1个}}/{问}_{\mathrm{小号}}^{-\mathrm{1个}}$可以准确估算出气体饱和度。第二种方法适用于缺少岩心饱和度数据的情况，该数据使用${问}_{\mathrm{P}}^{-\mathrm{1个}}/{问}_{\mathrm{小号}}^{-\mathrm{1个}}$用于评估气体饱和度。与常规电阻率方法相比，拟议的衰减方法作为一种非电方法，可为低电阻率储层岩石提供更准确的气体饱和度预测。最后，我们分析了低孔隙度岩石的衰减-饱和关系特征，并发现了可能的衰减机理。