Hydrocarbon Identification and Bedding Fracture Detection in Shale Gas Reservoirs Based on a Novel Seismic Dispersion Attribute Inversion Method

Abstract

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 DP evaluates the hydrocarbon enrichment by estimating the inelastic properties of shale associated with organic materials. The inverted anisotropic dispersion attribute Dε detects the development intensity of bedding fractures using frequency-dependent anisotropy owing to wave-induced fluid flow in parallel fractures. Synthetic tests indicate that DP can robustly estimate shale attenuation and Dε 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 DP and Dε anomalies, providing essential information for predicting potential shale gas reservoirs. Article Highlights: A novel seismic inversion method for anisotropy dispersion attributes is proposedP-wave velocity dispersion attribute is used to identify hydrocarbon enrichment in shaleAnisotropic dispersion attribute is used to detect bedding fractures in shale