Azimuthal AVO signatures of fractured poroelastic sandstone layers
Zhiqi Guo 1 4 Xiang-Yang Li 2 31 College of Geo-Exploration Science and Technology, Jilin University, 938 Xi Minzhu Street, Changchun 130021, China.
2 State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum (Beijing), Beijing 102249, China.
3 CNPC Key Laboratory of Geophysical Prospecting, China University of Petroleum (Beijing), Beijing 102249, China.
4 Corresponding author. Email: zhiqiguo@aliyun.com
Exploration Geophysics 48(1) 56-66 https://doi.org/10.1071/EG15050
Submitted: 2 June 2015 Accepted: 25 September 2015 Published: 27 October 2015
Abstract
Azimuthal P-wave amplitude variation with offset (AVO) offers a method for the characterisation of a naturally fractured system in a reservoir. This information is important for the analysis of fluid flow during production of, for example, oil, petroleum and natural gas. This paper provides a modelling scheme by incorporating the squirt-flow model for the prediction of velocity dispersion and attenuation with azimuthal reflectivity method for the calculation of frequency-dependent seismic responses. Azimuthal AVO responses from a fractured poroelastic sandstone layer encased within shale are investigated based on the proposed method. Azimuthal reflections are a combination of the dynamic information including the contrast in anisotropic properties, anisotropic propagation and attenuation within the layer, as well as tuning and interferences. Modelling results indicate that seismic responses from the top of the sandstone layer are dominated by reflection coefficients, and show azimuthal variations at far offset which is consistent with conventional azimuthal AVO theory. Reflections from the base, however, demonstrate complex azimuthal variations due to anisotropic propagation and attenuation of transmission waves within the layer. Tuning and interferences further complicate the azimuthal AVO responses for thinner layer thickness. The AVO responses of top reflections show no azimuthal variations for lower fluid mobility, while those of base reflections show visible and stable azimuthal variations even at near and moderate offsets for different fluid mobility. Results also reveal that it would be practical to investigate wavetrains reflected from the fractured layers that are regarded as integrated units, especially for thinner layers where reflections from the top and base are indistinguishable. In addition, near-offset stacked amplitudes of the reflected wavetrains show detectable azimuthal variations, which may offer an initial look at fracture orientations before AVO analysis.
Key words: attenuation, azimuthal AVO, dispersion, fluid mobility, fracture, reflectivity.
References
Batzle, M. L., Han, D. H., and Hofmann, R., 2006, Fluid mobility and frequency dependent seismic velocity – direct measurements: Geophysics, 71, N1–N9| Fluid mobility and frequency dependent seismic velocity – direct measurements:Crossref | GoogleScholarGoogle Scholar |
Chapman, M., 2003, Frequency dependent anisotropy due to meso-scale fractures in the presence of equant porosity: Geophysical Prospecting, 51, 369–379
| Frequency dependent anisotropy due to meso-scale fractures in the presence of equant porosity:Crossref | GoogleScholarGoogle Scholar |
Chapman, M., Maultzsch, S., Liu, E., and Li, X. Y., 2003, The effect of fluid saturation in an anisotropic multi-scale equant porosity model: Journal of Applied Geophysics, 54, 191–202
| The effect of fluid saturation in an anisotropic multi-scale equant porosity model:Crossref | GoogleScholarGoogle Scholar |
Chapman, M., Liu, E., and Li, X. Y., 2005, The influence of abnormally high reservoir attenuation on the AVO signature: The Leading Edge, 24, 1120–1125
| The influence of abnormally high reservoir attenuation on the AVO signature:Crossref | GoogleScholarGoogle Scholar |
Chapman, M., Liu, E., and Li, X. Y., 2006, The influence of fluid-sensitive dispersion and attenuation on AVO analysis: Geophysical Journal International, 167, 89–105
| The influence of fluid-sensitive dispersion and attenuation on AVO analysis:Crossref | GoogleScholarGoogle Scholar |
Ekanem, A. M., Li, X. Y., Chapman, M., and Main, I. G., 2015, Seismic attenuation in fractured porous media: insights from a hybrid numerical and analytical model: Journal of Geophysics and Engineering, 12, 210–219
| Seismic attenuation in fractured porous media: insights from a hybrid numerical and analytical model:Crossref | GoogleScholarGoogle Scholar |
Far, M. E., Sayers, C. M., Thomsen, L., Han, D., and Castagna, J. P., 2013a, Seismic characterization of naturally fractured reservoirs using amplitude versus offset and azimuth analysis: Geophysical Prospecting, 61, 427–447
| Seismic characterization of naturally fractured reservoirs using amplitude versus offset and azimuth analysis:Crossref | GoogleScholarGoogle Scholar |
Far, M. E., Thomsen, L., and Sayers, C. M., 2013b, Seismic characterization of naturally reservoirs with asymmetric fractures: Geophysics, 78, N1–N10
| Seismic characterization of naturally reservoirs with asymmetric fractures:Crossref | GoogleScholarGoogle Scholar |
Far, M. E., Hardage, B., and Wagner, D., 2014, Fracture parameter inversion for Marcellus Shale: Geophysics, 79, C55–C63
| Fracture parameter inversion for Marcellus Shale:Crossref | GoogleScholarGoogle Scholar |
Guo, Z. Q., Liu, C., Li, X. Y., and Lan, H. T., 2015, An improved method for the modeling of frequency-dependent amplitude-versus-offset variations: IEEE Geoscience and Remote Sensing Letters, 12, 63–67
| An improved method for the modeling of frequency-dependent amplitude-versus-offset variations:Crossref | GoogleScholarGoogle Scholar |
Hall, S. A., and Kendall, J., 2003, Fracture characterization at Valhall: application of P-wave amplitude variation with offset and azimuth (AVOA) analysis to a 3D ocean-bottom dataset: Geophysics, 68, 1150–1160
| Fracture characterization at Valhall: application of P-wave amplitude variation with offset and azimuth (AVOA) analysis to a 3D ocean-bottom dataset:Crossref | GoogleScholarGoogle Scholar |
Landrø, M, and Tsvankin, I, 2007, Seismic critical-angle reflectometry: a method to characterize azimuthal anisotropy? Geophysics, 72, D41–D50
| Seismic critical-angle reflectometry: a method to characterize azimuthal anisotropy?Crossref | GoogleScholarGoogle Scholar |
MacBeth, C., 1999, Azimuthal variation in P-wave signatures due to fluid flow: Geophysics, 64, 1181–1192
| Azimuthal variation in P-wave signatures due to fluid flow:Crossref | GoogleScholarGoogle Scholar |
Pérez, M. A., Gibson, R. L., and Toksöz, M. N., 1999, Detection of fracture orientation using azimuthal variation of P-wave AVO responses: Geophysics, 64, 1253–1265
| Detection of fracture orientation using azimuthal variation of P-wave AVO responses:Crossref | GoogleScholarGoogle Scholar |
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 |
Rüger, A., and Tsvankin, I., 1995, Azimuthal variation of AVO response for fractured reservoirs: 65th Annual International Meeting, SEG, Expanded Abstracts, 1103–1106.
Rüger, A., and Tsvankin, I., 1997, Using AVO for fracture detection: analytic basis and practical solutions: The Leading Edge, 16, 1429–1434
| Using AVO for fracture detection: analytic basis and practical solutions:Crossref | GoogleScholarGoogle Scholar |
Rutherford, S. R., and Williams, R. H., 1989, Amplitude-versus-offset variations in gas sands: Geophysics, 54, 680–688
| Amplitude-versus-offset variations in gas sands: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. 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 |
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 |
