Azimuthal seismic responses from shale formation based on anisotropic rock physics and reflectivity method: a case study from south-west China
Neng Lu 1 Cai Liu 1 Zhiqi Guo 1 5 Xiwu Liu 2 3 41 College of Geo-Exploration Science and Technology, Jilin University, 938 Xi Minzhu Street, Changchun 130021, China.
2 State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing 100083, China.
3 SinoPEC Key Laboratory of Shale Oil/Gas Exploration and Production Technology, Beijing 100083, China.
4 SinoPEC Petroleum Exploration and Production Research Institute, Beijing 100083, China.
5 Corresponding author. Email: zhiqiguo@aliyun.com
Exploration Geophysics 49(3) 363-371 https://doi.org/10.1071/EG16097
Submitted: 8 August 2016 Accepted: 4 April 2017 Published: 17 May 2017
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.
Key words: anisotropy, AVAz, reflectivity, rock physics, shale.
References
Banik, N. C., 1984, Velocity anisotropy of shales and depth estimation in the North Sea basin: Geophysics, 49, 1411–1419| Velocity anisotropy of shales and depth estimation in the North Sea basin:Crossref | GoogleScholarGoogle Scholar |
Booth, D. C., and Crampin, S., 1983, The anisotropic reflectivity technique: theory: Geophysical Journal International, 72, 755–766
| The anisotropic reflectivity technique: theory:Crossref | GoogleScholarGoogle Scholar |
Deng, J. X., Wang, H., Zhou, H., Liu, Z. H., Song, L. T., and Wang, X. B., 2015, Microtexture, seismic rock physical properties and modeling of Longmaxi Formation Shale: Chinese Journal of Geophysics, 58, 2123–2216
Downton, J. E., and Roure, B., 2015, Interpreting azimuthal Fourier coefficients for anisotropic and fracture parameters: Interpretation, 3, ST9–ST27
| Interpreting azimuthal Fourier coefficients for anisotropic and fracture parameters:Crossref | GoogleScholarGoogle Scholar |
Fryer, G. J., and Frazer, L. N., 1984, Seismic waves in stratified anisotropic media: Geophysical Journal International, 78, 691–710
| Seismic waves in stratified anisotropic media:Crossref | GoogleScholarGoogle Scholar |
Fryer, G. J., and Frazer, L. N., 1987, Seismic waves in stratified anisotropic media - ii.elastodynamic eigensolutions for some anisotropic systems: Geophysical Journal of the Royal Astronomical Society, 91, 73–101
| Seismic waves in stratified anisotropic media - ii.elastodynamic eigensolutions for some anisotropic systems:Crossref | GoogleScholarGoogle Scholar |
Gilbert, F., and Backus, G. E., 1966, Propagator matrices in elastic wave and vibration problems: Geophysics, 31, 326–332
| Propagator matrices in elastic wave and vibration problems:Crossref | GoogleScholarGoogle Scholar |
Jiang, Z., Ling, G., and Chao, L., 2013, Lithofacies and sedimentary characteristics of the Silurian Longmaxi Shale in the southeastern Sichuan Basin, China: Journal of Palaeogeography, 2, 238–251
Johnston, J. E., and Christensen, N. I., 1995, Seismic anisotropy of shales: Journal of Geophysical Research: Solid Earth, 100, 5991–6003
| Seismic anisotropy of shales:Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2MXmtF2gt78%3D&md5=f6e8a45c773c2635fd9fa2ce9e951579CAS |
Kennett, B. L. N., 1983, Seismic wave propagation in stratified media: Cambridge University Press.
Kumar, D., 2013, Applying Backus averaging for deriving seismic anisotropy of a long-wavelength equivalent medium from well-log data: Journal of Geophysics and Engineering, 10, 055001
| Applying Backus averaging for deriving seismic anisotropy of a long-wavelength equivalent medium from well-log data:Crossref | GoogleScholarGoogle Scholar |
Mallick, S., and Frazer, L. N., 1988, Rapid computation of multioffset vertical seismic profile synthetic seismograms for layered media: Geophysics, 53, 479–491
| Rapid computation of multioffset vertical seismic profile synthetic seismograms for layered media:Crossref | GoogleScholarGoogle Scholar |
Maultzsch, S., Horne, S., Archer, S., and Burkhardt, H., 2003, Effects of an anisotropic overburden on azimuthal amplitude analysis in horizontal transverse isotropic media: Geophysical Prospecting, 51, 61–74
| Effects of an anisotropic overburden on azimuthal amplitude analysis in horizontal transverse isotropic media:Crossref | GoogleScholarGoogle Scholar |
Qian, Z., Li, X. Y., and Chapman, M., 2007, Azimuthal variations of PP and PS-wave attributes: a synthetic study: SEG Technical Program, Expanded Abstracts, 184–188.
Rüger, A., 1998, Variation of P-wave reflectivity with offset and azimuth in anisotropic media: Geophysics, 63, 935–947
| Variation of P-wave reflectivity with offset and azimuth in anisotropic media:Crossref | GoogleScholarGoogle Scholar |
Sayers, C. M., 2005, Seismic anisotropy of shales: Geophysical Prospecting, 53, 667–676
| Seismic anisotropy of shales:Crossref | GoogleScholarGoogle Scholar |
Sayers, C. M., and Rickett, J. E., 1997, Azimuthal variation in AVO response for fractured gas sands: Geophysical Prospecting, 45, 165–182
| Azimuthal variation in AVO response for fractured gas sands:Crossref | GoogleScholarGoogle Scholar |
Schoenberg, M., and Douma, J., 1988, Elastic wave propagation in media with parallel fractures and aligned cracks: Geophysical Prospecting, 36, 571–590
| Elastic wave propagation in media with parallel fractures and aligned cracks:Crossref | GoogleScholarGoogle Scholar |
Schoenberg, M., and Helbig, K., 1997, Orthorhombic media: modeling elastic wave behavior in a vertically fractured earth: Geophysics, 62, 1954–1974
| Orthorhombic media: modeling elastic wave behavior in a vertically fractured earth:Crossref | GoogleScholarGoogle Scholar |
Schoenberg, M., and Muir, F., 1989, A calculus for finely layered anisotropic media: Geophysics, 54, 581–589
| A calculus for finely layered anisotropic media:Crossref | GoogleScholarGoogle Scholar |
Schoenberg, M. A., and Protázio, J., 1992, ‘Zoeppritz’ rationalized and generalized to anisotropy: Journal of Seismic Exploration, 1, 125–144
Schoenberg, M. A., Dean, S., and Sayers, C. M., 1999, Azimuth-dependent tuning of seismic waves reflected from fractured reservoirs: Geophysics, 64, 1160–1171
| Azimuth-dependent tuning of seismic waves reflected from fractured reservoirs:Crossref | GoogleScholarGoogle Scholar |
Sen, M. K., and Roy, I. G., 2003, Computation of differential seismograms and iteration adaptive regularization in prestack waveform inversion: Geophysics, 68, 2026–2039
| Computation of differential seismograms and iteration adaptive regularization in prestack waveform inversion:Crossref | GoogleScholarGoogle Scholar |
Thomsen, L., 1986, Weak elasticanisotropy: Geophysics, 51, 1954–1966
| Weak elasticanisotropy:Crossref | GoogleScholarGoogle Scholar |
Vavryčuk, V., and Pšenčík, I., 1998, PP-wave reflection coefficients in weakly anisotropic elastic media: Geophysics, 63, 2129–2141
| PP-wave reflection coefficients in weakly anisotropic elastic media:Crossref | GoogleScholarGoogle Scholar |
Woodhouse, J. H., 1974, Surface waves in laterally varying layered structure: Geophysical Journal International, 37, 461–490
| Surface waves in laterally varying layered structure:Crossref | GoogleScholarGoogle Scholar |
Zoeppritz, K., 1919, Erdbebenwellen VIIIB, On the reflection and propagation of seismic waves: Gottinger Nachrichten, I, 66–84