Because of the particular depositional mode,black organic matter-rich shales are generally characterized by strong velocity anisotropy;however,most researches on shale are on the basis of isotropic theory,which obviously ignores the geological characteristics of shale.In this paper,anisotropic parameters of shale are calculated by combining rock mechanical measurements in the laboratory with the empirical methods from the literature.On the one hand,the parameters are used to investigate their effects on the calculation of velocity versus bedding direction and rock mechanical parameters,and the result shows that the anisotropic characteristics of shale cannot be neglected when the dip angle of the strata is large.On the other hand,little difference between AVO responses of anisotropic and isotropic methods when the incidence angle is less than 40° indicates the feasibility of isotropic pre-stack seismic inversion in predicting shale "sweet spot".
Guo X S, Li Y P, Liu R B , et al. Characteristics and controlling factors of micro-pore structures of Longmaxi Shale Play in the Jiaoshiba area,Sichuan Basin[J]. Natural Gas Industry, 2014,34(6):9-16.
[2]
Vernik L, Liu X . Velocity anisotropy in shales:A petrophyscial study[J]. Geophysics, 1997,62(2):521-532.
doi: 10.1190/1.1444162
[3]
Vernik L , Milovac J . Rock physics of organic shales[J].The Leading Edge, 2011, Special Section:Shales:318-323.
[4]
Sayer C . The effect of kerogen on the elastic anisotropy of organic-rich shales[J]. Geophysics, 2013,78(2):65-74.
doi: 10.1190/GEO2012-0309.1
[5]
Sayers C . Seismic anisotropy of shales[J]. Geophysical Prospecting, 2005,63:667-676.
Guo T L, Liu R B . Implications from marine shale gas exploration breakthrough in complicated structural area at high thermal stage:Taking Longmaxi Formation in well JY1 as an example[J]. Natural Gas Geoscience, 2013,24(4):613-650.
[7]
Thomsen L . Weak elastic anisotropy[J]. Geophysics, 1986,51(10):1954-66.
doi: 10.1190/1.1442051
Tang J . Experimental study of static and dynamic moduli for anisotropic rock[J]. Chinese Journal of Rock Mechanics and Engineering, 2014,33(s1):3785-3191.
[9]
Luan X Y, Di B R, Wei J X, et al. Laboratory measurements of brittleness anisotropy in synthetic shale with different cementation [C]//Expanded Abstracts of the 84 th Annual SEG Meeting,Society of Exploration Geophysicists , 2014: 26-31.
[10]
Ryan-Grigor S . Empirical relationships between transverse isotropy parameters and VP/VS: Implications for AVO[J]. Geophysics, 1997,62(5):1359-1364.
doi: 10.1190/1.1444239
[11]
Li Y Y . An empirical method for estimation of anisotropic parameters in clastic rocks[J]. The Leading Edge, 2006,25:706-711.
doi: 10.1190/1.2210052
[12]
Hiroki S . Mechanical properties of shale gas reservoir rocks and its relation to the insi-tu stress variation observed in shale gas reservoir[D]. Stanford University, 2012: 38-44.
[13]
Sayers C . The effect of anisotropy on the Young’s moduli and Poisson’s ratios of shales[J]. Geophysical Prospecting, 2013,61:416-426.
doi: 10.1111/j.1365-2478.2012.01130.x
[14]
Deng J X, Shen H, Xu Z H , et al. Dynamic elastic properties of the Wufeng-Longmaxi formation shale in the southeast margin of the Sichuan Basin[J]. Journal Geophysics Engineering, 2014,11:1-11.
[15]
陈颙, 黄庭芳 . 岩石物理学[M]. 北京: 北京大学出版社, 2001: 35-38.
[15]
Chen Y, Huang T F. Rock Phycis[M]. Beijing: Peking University Press, 2001: 35-38.
Chen Z Q . Quantitative seismic prediction technique of marine shale TOC and its application:A case from the Longmaxi Shale Play in the Jiaoshiba area,SichuanBasin[J]. Natural Gas Industry, 2014,34(6):24-29.
[17]
Sena A, Castillo G , Chesser K . Seismic reservoir characterization in resource shale plays:Stress analysis and sweet spot discrimination[J].The Leading Edge, 2011, Special Section:Practical Applications of Anisotropy: 758-764.
doi: 10.1190/1.3609090
[18]
Wright J . The effects of transverse isotropy on reflection amplitude versus offset[J]. Geophsics, 1987,52(4):564-567.
doi: 10.1190/1.1442325
[19]
Thomsen L. Weak anisotropic reflections,Offset Dependent Reflectivity:Theory and Practice of AVO analysis [C]//Expanded Abstracts of the 73 rd Annual SEG Meeting,Society of Exploration Geophysicists , 2013.
[20]
Ruger A. Reflection coefficients and azimuthal AVO Analysis in anisotropic media [C]//SEG Geophysical Monograph Series Number 10,Society Exploration Geophysicists, 2002.
[21]
Rickman R, Mullen M, Petre E. A practical use of shale petrophysics for stimulation design optimization:All shale plays are not clones of the Barnett Shale [C]//Denver:SPE Annual Technical Conference and Exhibition, 2008.
[22]
Thomsen L. On the use of isotropic parameters λ,E,ν,K to understand anisotropic shale behavior [C]//Expanded Abstracts of the 83 rd Annual SEG Meeting,Society of Exploration Geophysicists , 2013: 320-324.