地震资料中的多尺度断裂与流体响应特征:数值模拟分析
摘要
流体在断裂和岩石骨架间的交换被认为是影响岩石弹性参数各向异性的主要原因,理论研究表明断裂尺度同样对弹性参数的各向异性也有影响.为了说明两者对各向异性影响以实现多尺度断裂裂隙的识别,本文在等效介质模型的基础上,应用数值分析的方法研究速度和衰减(1/Q)随多尺度断裂、频率和流体因子变化规律.结果表明介质弹性参数是频率依赖的,并且参数中存在衰减项,而这种频率依赖性与介质物性参数中的断裂尺度及流体性质存在一定的联系;当断裂定向分布时,参数结果显示为各向异性;不同断裂尺度具有不同的波速频散特性,剪切波分裂程度依赖于频率,断裂尺度起着控制作用,高频时对小尺度的敏感,低频段对大尺度敏感.在地震频段Thomsen参数随着频率的增大而减小,随着断裂尺寸的增大而减小.因此地震数据可能区分断裂和微裂隙引起各向异性,从而可测量断裂尺度.
The exchange of fluid between fractures and rock matrix is considered to be a main factor influencing the calculated anisotropic elastic properties. Theoretical study shows that the fracture scales also have the same impact on it. To identify the multi-scale fracture, numerical analysis was introduced to analyze the variation of velocity and attenuation with the changes of the multi-scale fracture, frequency and fluid factor based on the equivalent medium model. The results show that the elastic parameters are frequency dependent, including the attenuation. This frequency dependence is related to the fracture scale and fluid properties of rocks. Within the various fracture scales with different velocity dispersion, the shear wave splitting depends on the frequency, and the scale of fracture is the leading factor, small scale is sensitive to high frequency, while low frequency to large scale. In the seismic frequency band, Thomsen parameters decreased with increasing frequency as well as the increasing of the fracture scale. Thus, seismic data may be an indication to distinguish the anisotropy caused by the fracture or micro-crack and also used to distinguish fracture scale.
The exchange of fluid between fractures and rock matrix is considered to be a main factor influencing the calculated anisotropic elastic properties. Theoretical study shows that the fracture scales also have the same impact on it. To identify the multi-scale fracture, numerical analysis was introduced to analyze the variation of velocity and attenuation with the changes of the multi-scale fracture, frequency and fluid factor based on the equivalent medium model. The results show that the elastic parameters are frequency dependent, including the attenuation. This frequency dependence is related to the fracture scale and fluid properties of rocks. Within the various fracture scales with different velocity dispersion, the shear wave splitting depends on the frequency, and the scale of fracture is the leading factor, small scale is sensitive to high frequency, while low frequency to large scale. In the seismic frequency band, Thomsen parameters decreased with increasing frequency as well as the increasing of the fracture scale. Thus, seismic data may be an indication to distinguish the anisotropy caused by the fracture or micro-crack and also used to distinguish fracture scale.
引文
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[27]Yang D H,Zhang Z J.Effects of the Biot and the squirt-flowcoupling interaction on anisotropic elastic waves.ChineseScience Bulletin,2000,45(23):2130-2138.
[28]Lan H Q,Zhang Z J.Seismic wavefield modeling in mediawith fluid-filled fractures and surface topography.AppliedGeophysics,2012,9(3):301-312.
[29]徐涛,徐果明,高尔根等.三维复杂介质的块状建模和试射射线追踪.地球物理学报,2004,47(6):1118-1126.Xu T,Xu G M,Gao E G,et al.Block modeling and shootingray tracing in complex 3-D media.Chinese J.Geophys.(inChinese),2004,47(6):1118-1126.
[30]Xu T,Xu G M,Gao E G,et al.Block modeling andsegmentally iterative ray tracing in complex 3D media.Geophysics,2006,71(3):T41-T51.
[31]Xu T,Zhang Z J,Gao E G,et al.Segmentally iterative raytracing in complex 2Dand 3Dheterogeneous block models.Bull.Seismol.Soc.Am.,2010,100(2):841-850.
[32]Liu K,Zhang Z J,Hu J F,et al.Frequency band-dependence of S-wave splitting in China mainland and itsimplications.Science in China(Series D),2001,44(7):659-665.
[33]Maultzsch S,Chapman M,Liu E R,et al.Modellingfrequency-dependent seismic anisotropy in fluid-saturatedrock with aligned fractures:implication of fracture sizeestimation from anisotropic measurements.GeophysicalProspecting,2003,51(5):381-392.
[34]Dvorkin J,Nur A.Dynamic poroelasticity:A unified modelwith the squirt and the Biot mechanisms.Geophysics,1993,58(4):524-533.
[35]Tsvankin I.Anisotropic parameters and P-wave velocity fororthorhombic media.Geophysics,1997,62(4):1292-1309.
[2]Schoenberg M.Elastic wave behavior across linear slipinterfaces.Journal of the Acoustical Society of America,1980,68(5):1516-1521.
[3]Schoenberg M,Douma J.Elastic wave propagation in mediawith parallel fractures and aligned cracks.Geophys.Prospect.,1988,36(6):571-590.
[4]Hudson J A.Wave speeds and attenuation of elastic waves inmaterial containing cracks.Geophys.J.Int.,1981,64(1):133-150.
[5]Hudson J A,Liu E,Crampin S.The mechanical propertiesof materials with interconnected cracks and pores.Geophys.J.Int.,1996,124(1):105-112.
[6]Nishizawa O.Seismic velocity anisotropy in a mediumcontaining oriented cracks-transversely isotropic case.Journal ofPhysics of the Earth,1982,30(4):331-347.
[7]Thomsen L.Weak elastic anisotropy.Geophysics,1986,51(10):1954-1966.
[8]Thomsen L.Elastic anisotropy due to aligned cracks inporous rock.Geophys.Prospect.,1995,43(6):805-829.
[9]Tod S R.The effects on seismic waves of interconnectednearly aligned cracks.Geophysical Journal International,2001,146(1):249-263.
[10]Van der Kolk C M,Guest W S,Potters J H H M.The 3Dshear experiment over the Natih field in Oman:the effect offracture-filling fluids on shear propagation.Geophys.Prospect.,2001,49(2):179-197.
[11]Chapman M.Frequency-dependent anisotropy due to meso-scale fractures in the presence of equant porosity.Geophys.Prospect.,2003,51(5):369-379.
[12]Brown R J S,Korringa J.On the dependence of the elasticproperties of a porous rock on the compressibility of the porefluid.Geophysics,1975,40(4):608-616.
[13]Chapman M,Zatsepin S V,Crampin S.Derivation of amicrostructural poroelastic model.Geophys.J.Int.,2002,151(2):427-451.
[14]Chapman M H.Modelling the wide-band laboratory responseof rock samples to fluid and pressure changes[Ph.D.thesis].Edinburgh:University of Edinburgh,2001.
[15]Chapman M,Maultzsch S,Liu E R,et al.The effect of fluidsaturation in an anisotropic multi-scale equant porositymodel.J.Appl.Geophys.,2003,54(3-4):191-202.
[16]Chapman M,Liu E R,Li X Y.The influence of fluidsensitive dispersion and attenuation on AVO analysis.Geophysical Journal International,2006,167(1):89-105.
[17]Champan M.Modeling the effect of multiple sets ofmesoscale fractures in porous rock on frequency-dependentanisotropy.Geophysics,2009,74(6):D97-D103.
[18]张中杰,滕吉文,贺振华.EDA介质中地震波速度、衰减与品质因子方位异性研究.中国科学(E辑),1999,29(6):569-574.Zhang Z J,Teng J W,He Z H.The detection attenuationresearch on seismic wave velocity‘Attenuation’qualityfactor of EDA medium.Science in China(Ser.E)(inChinese),2009,29(6):569-574.
[19]张忠杰.多分量地震资料的各向异性处理与解释方法.哈尔滨:黑龙江教育出版社,2002.Zhang Z J.Multi-component Seismic Data AnisotropicProcessing and Interpretation Methods(in Chinese).Harbin:Heilongjiang Education Press,2002.
[20]何樵登,张中杰.横向各向同性介质中地震波及其数值模拟.长春:吉林大学出版社,1996.He Q D,Zhang Z J.Wave in Transversely Isotropic Mediumand Numerical Modelling(in Chinese).Changchun:JilinUniversity Press,1996.
[21]Zhang Z J,Teng J,Badal J,et al.Construction of regionaland local seismic anisotropic structures from wide-angleseismic data:crustal deformation in the southeast of China.Journal of Seismology,2009,13(2):241-252.
[22]Zhang Z J,Wang G J,Harris J M.Multi-componentwavefield simulation in viscous extensively dilatancy anisotropicmedia.Phys.,Earth Planet.Inter.,1999,114(1-2):25-38.
[23]Yang D H,Liu E R,Zhang Z J,et al.Finite-differencemodelling in two-dimension anisotropic media using a flux-corrected transport technique.Geophys.J.Int.,2002,148(2):320-328.
[24]Yang D H,Wang S Q,Zhang Z J,et al.N-times absorbingbounding conditions for compact finite-difference modeling ofacoustic and elastic wave propagation in the 2DTI medium.Bull.Seismol.Soc.Am.,2003,93(6):2389-2401.
[25]Yang D H,Zhang Z J.Poroelastic wave equation includingthe Biot/Squirt mechanism and the solid/fluid couplinganisotropy.Wave Motion,2002,35(3):223-245.
[26]Zheng H S,Zhang Z J,Liu E R.Non-linear seismic wavepropagation in anisotropic media using the flux-correctedtransport technique.Geophysical Journal International,2006,165(3):943-956.
[27]Yang D H,Zhang Z J.Effects of the Biot and the squirt-flowcoupling interaction on anisotropic elastic waves.ChineseScience Bulletin,2000,45(23):2130-2138.
[28]Lan H Q,Zhang Z J.Seismic wavefield modeling in mediawith fluid-filled fractures and surface topography.AppliedGeophysics,2012,9(3):301-312.
[29]徐涛,徐果明,高尔根等.三维复杂介质的块状建模和试射射线追踪.地球物理学报,2004,47(6):1118-1126.Xu T,Xu G M,Gao E G,et al.Block modeling and shootingray tracing in complex 3-D media.Chinese J.Geophys.(inChinese),2004,47(6):1118-1126.
[30]Xu T,Xu G M,Gao E G,et al.Block modeling andsegmentally iterative ray tracing in complex 3D media.Geophysics,2006,71(3):T41-T51.
[31]Xu T,Zhang Z J,Gao E G,et al.Segmentally iterative raytracing in complex 2Dand 3Dheterogeneous block models.Bull.Seismol.Soc.Am.,2010,100(2):841-850.
[32]Liu K,Zhang Z J,Hu J F,et al.Frequency band-dependence of S-wave splitting in China mainland and itsimplications.Science in China(Series D),2001,44(7):659-665.
[33]Maultzsch S,Chapman M,Liu E R,et al.Modellingfrequency-dependent seismic anisotropy in fluid-saturatedrock with aligned fractures:implication of fracture sizeestimation from anisotropic measurements.GeophysicalProspecting,2003,51(5):381-392.
[34]Dvorkin J,Nur A.Dynamic poroelasticity:A unified modelwith the squirt and the Biot mechanisms.Geophysics,1993,58(4):524-533.
[35]Tsvankin I.Anisotropic parameters and P-wave velocity fororthorhombic media.Geophysics,1997,62(4):1292-1309.
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