Abstract

Prediction of hydrocarbon enrichment and natural fractures is significant for sweet spot characterization in shale gas reservoirs. However, it is difficult to estimate reservoir properties using conventional seismic techniques based on elastic and isotropic assumptions. Considering that the viscoelastic anisotropic model better represents organic shale, we propose a new seismic inversion method to improve shale gas characterization by incorporating the anisotropic reflectivity theory in the frequency-dependent inversion scheme. The computed P-wave velocity dispersion attribute D_P evaluates the hydrocarbon enrichment by estimating the inelastic properties of shale associated with organic materials. The inverted anisotropic dispersion attribute D_ε detects the development intensity of bedding fractures using frequency-dependent anisotropy owing to wave-induced fluid flow in parallel fractures. Synthetic tests indicate that D_P can robustly estimate shale attenuation and D_ε is sensitive to the frequency-dependent anisotropy of shale. The results are validated by reservoir properties measured in gas-producing boreholes and rock physical modeling analysis, supporting the applicability of the dispersion attributes for hydrocarbon identification and bedding fracture detection. The predicted hydrocarbon enrichment and the development of bedding fractures correlate with the structural characteristics of the shale formation. The depth-related shale properties can be described by improving the geological understanding of the study area. Finally, favorable areas with high hydrocarbon enrichment and extensive development of bedding fractures are identified by simultaneously considering high D_P and D_ε anomalies, providing essential information for predicting potential shale gas reservoirs.

Article Highlights

• A novel seismic inversion method for anisotropy dispersion attributes is proposed

• P-wave velocity dispersion attribute is used to identify hydrocarbon enrichment in shale

• Anisotropic dispersion attribute is used to detect bedding fractures in shale

中文翻译：

---

基于新型地震频散属性反演方法的页岩气藏油气识别与层理裂缝检测

摘要

油气富集和天然裂缝的预测对于页岩气储层的甜点表征具有重要意义。然而，使用基于弹性和各向同性假设的传统地震技术很难估计储层特性。考虑到粘弹性各向异性模型更好地代表有机质页岩，我们提出了一种新的地震反演方法，通过将各向异性反射率理论结合到频率相关的反演方案中来改进页岩气的表征。计算出的P波速度频散属性D _P通过估计与有机材料相关的页岩的非弹性特性来评估烃富集。反各向异性色散属性D _ε由于平行裂缝中波浪引起的流体流动，使用频率相关的各向异性检测层理裂缝的发育强度。综合测试表明，D _P可以稳健地估计页岩衰减和D _ε对页岩的频率相关各向异性敏感。结果通过产气钻孔中测量的储层特性和岩石物理建模分析得到验证，支持分散属性在烃识别和层理裂缝检测中的适用性。预测的油气富集和层理裂缝的发育与页岩地层的构造特征相关。可以通过提高对研究区的地质认识来描述与深度相关的页岩特性。最后，同时考虑高D _P和D _ε，确定了油气高富集和层理裂缝广泛发育的有利区。异常，为预测潜在的页岩气藏提供重要信息。

文章重点

• 提出了一种新的各向异性频散属性地震反演方法

• P波速度频散属性用于识别页岩油气富集

• 各向异性分散属性用于检测页岩层理裂缝