Azimuthal seismic responses from shale formation based on anisotropic rock physics and reflectivity method: a case study from south-west China. Issue 3 (1st June 2018)

• Record Type: Journal Article
• Authors: Lu, Neng; Liu, Cai; Guo, Zhiqi; Liu, Xiwu
• Is Part Of: Exploration geophysics. Volume 49:Issue 3(2018)
• Page Start: 363
• Page End: 371
• Publication Date: 2018-06-01
• Subjects: anisotropy -- AVAz -- reflectivity -- rock physics -- shale; Geophysics -- Periodicals; Prospecting -- Geophysical methods -- Periodicals; 622.15
• DOI: 10.1071/EG16097
• Languages: English
• ISSNs: 0812-3985

Abstract

Abstract : Due to intrinsic anisotropy related to preferred alignment of clay particles and the existence of vertical or high angle fractures, shales usually present orthorhombic anisotropy. The objective of this study was to build anisotropic rock physics models for shales at the seismic scale. Based on the well-log and Formation Micro Imager (FMI) log data from a shale formation in the Sichuan Basin in south-west China, we derive an orthorhombic model at the seismic scale by using Schoenberg and Helbig's method and generalised Backus averaging method in the rock physics workflow. In order to understand the relationship between physical properties of the rock physics model and seismic wave propagation, we apply the simplified reflectivity method to calculate seismic responses for amplitude variation with azimuth (AVAz) analysis. The method is based on the scheme of anisotropic reflectivity method which is commonly used to simulate the full-wave field in stratified anisotropic media, in analogy with the formula of horizontal slowness components in Schoenberg and Protázio's method. The AVAz analysis is conducted on the seismograms of PP-wave, radial and transverse components of PS-wave. The results show that overburden effects caused by wave propagation in anisotropic media can't be ignored. Azimuthal variations in amplitudes of both PP-wave and radial component of PS-wave can be used to indicate strikes of fractures, while PS-wave appears to be more sensitive. Abstract : We have constructed an anisotropic rock physics model at the seismic scale for shales, and applied it to the Longmaxi Shale in the Sichuan Basin, south-west China. The simplified reflectivity method is proposed to calculate seismic responses for amplitude variation with offset and azimuth (AVAz) analysis.