球面波的反射P波AVO分析

本文对球面波反射P波反射系数计算公式进行了推导,根据推导公式计算出第I类AVO和第Ⅲ类AVO介质中反射系数及相位随入射角的变化,并与基于平面波的Zoeppritz方程计算的结果进行对比.结果显示,对于第I类AVO介质,球面波反射系数在临界角附近较基于平面波的Zoeppritz方程计算结果更精确;同时受界面深度的影响较大,随深度的增加,球面波AVO趋势接近平面波AVO.最后,通过数值模拟技术,对模型数据和实际数据进行模拟,对平面波AVO道集和球面波AVO道集进行了验证分析.浅层的第I类AVO现象,在近临界角和超临界角处折射引起反射系数与相位的变化较大,对于第Ⅲ类AVO现象,由于不存在临界角问题,球面波模拟结果与基于平面波的Zoeppritz计算结果差别较小.上述计算分析,可为实际资料的大偏移距道集的AVO分析提供理论基础.     

考虑球面波前曲率的低频频变反演

实际地震采集中的点震源激发产生球面波场,反射界面处球面波前曲率的改变会导致反射波的振幅和相位随频率而变化,而基于高频远场近似的常规平面波勘探忽略了球面波前曲率的低频频变效应.为此,本文首先利用高精度的数值积分法和有限差分法模拟了柱坐标系下的反射波记录,揭示了球面波反射系数的低频频变特征.为解决常规叠前反演需要多个偏移距...     

基于黏弹性Chapman-Kelvin模型的裂缝储层频变AVAZ反演研究

为了在地震资料和裂缝储层特征之间建立联系,对裂缝储层采用了等效介质模型.而传统的等效介质模型未充分考虑非完全弹性介质理论和基于频变各向异性理论的双相或多相流体假设,也不能对实际裂缝储层中的地震波频散和衰减现象提供准确合理的解释,并且储层参数的反演研究对裂缝储层的定性预测和定量描述举足轻重.为此,本文首先根据所提出的黏弹性Chapman-Kelvin动态等效介质模型,该模型考虑了耦合的双相流体假设、黏弹性理论、喷射流以及斑块效应,并在此基础上分析了裂缝储层参数(主要为裂缝密度、裂缝长度、孔隙度和含水饱和度)对地震波频变特征的影响.然后基于黏弹性Chapman-Kelvin模型与Schoenberg和Protazio概括的Zoeppritz方程所计算出的频变反射系数,分析了反射PP波和PS波的频变AVAZ(Amplitude Versus Angle and Azimuth)特性和PP波频变反射系数与裂缝储层参数的关系.同时考虑到发生地震频散时,反射系数和频率产生关系,构建了在角度、方位和时间域内的新型正演方程.最后,基于PP波频变反射系数对裂缝密度、裂缝长度、孔隙度和含水饱和度的变化有较...     

薄层VTI介质中地震反射系数及相位响应

本文从波动方程出发,推导了平面波在砂泥岩薄互层VTI介质中界面上的反射系数和相位特征;结果表明反射系数与反射系数的相位有关,以及反射系数会发生接近-90°相位旋转,理论上证明了Zeng[6,7]的结论.模型数值试验及实际资料处理结果均表明,地震反射波的薄层与厚层的响应特征存在明显的差异.因此当前广泛应用的AVO及波阻抗反演等储层预测和油气检测技术等,均需要充分考虑并完善薄层的影响效应.     

非弹性层状介质地震波频变AVO响应模拟及分析

以非弹性层状介质为模型,基于广义传播矩阵理论计算地震波频变反射系数,算法中同时考虑了与频散和衰减有关的地层岩性因素,以及与薄互层有关的地层结构因素.实现了岩石物理模型、反射系数这两个计算过程的"无缝"连接,精确考虑了由复数弹性模量表示的地层非弹性因素,也为在同一反射模型中考虑源于不同物理机制的频散与衰减提供了方法.数值模拟结果验证了算法的有效性和稳定性,计算结果表明,非弹性薄层的反射振幅随频率先增加后减小,不一定表现常规"低频亮点"异常;同时,薄互层条件下的频散与衰减使得地震反射波的频谱以及AVO特征呈现与频率相关的复杂变化.本文完善了频变AVO算法,为含油气储层频变AVO响应的模拟和分析提供了方法.     

裂隙等效TTI介质qP波反射特征研究

研究倾斜裂隙介质的qP渡反射特征对于裂隙储层预测具有指导意义.本文基于Hudson等效理论,推导了倾斜裂隙等效TTI介质PP波反射系数公式,该公式直观地建立了反射系数与裂隙参数之间的关系,反应了裂隙密度、裂隙充填物以及裂隙倾角对反射系数的影响.基于该公式研究了裂隙等效TTI介质PP波反射系数对裂隙充填物和裂隙密度的敏感性,并对其随裂隙倾角的变化情况进行了研究和总结.结果表明,裂隙充填物的性质对于PP波反射系数具有很大的影响,含饱和气的裂隙介质的PP波反射系数曲线较无裂隙介质的反射系数曲线变化较大,无论是反射系数的梯度还是截距均发生了大的改变,而且随裂隙倾角成反比变化,而当裂隙介质含饱和水时,其反射系数曲线相对于无裂隙介质的反射系数曲线变化很小;裂隙密度同样受到裂隙倾角的影响,当裂隙介质的裂隙密度越大时,其PP波反射系数随裂隙倾角变化也越大.     

用对称映射ARMA模型的零极点研究子波相位对反射系数序列反演的影响

为研究地震子波相位对反射系数序列反演的影响,在自回归滑动平均(ARMA)模型描述子波的基础上,提出采用z域对称映射ARMA模型零极点的方法构造了一系列相同振幅谱、不同相位谱的地震子波,并结合谱除法对人工合成地震记录进行反射系数序列反演.理论分析表明,子波相位估计不准时反射系数序列反演结果中残留一个纯相位滤波器,该纯相位滤波器的相位谱为真实子波和构造子波的相位谱之差.采用丰度和变分作为评价方法,在反演结果中确定出真实的或准确的反射系数序列.仿真实验和实际数据处理结果也验证了子波相位对反射系数序列反演的影响规律和评价方法的有效性,为进一步提高反射系数序列反演结果精度指明了研究方向.     

基于广义S变换的地震资料振幅谱补偿和相位谱校正方法研究（英文）

由于地下介质对地震波振幅的影响和地震波频散因素,地震波振幅和相位随时间、空间及频率的变化而发生改变,本文提出一种基于广义S变换的振幅谱补偿和相位谱校正新方法。该方法在S域中分为振幅谱补偿和相位谱校正两个步骤进行处理:振幅谱补偿是在地震记录可靠频带范围内恢复反射系数的振幅谱,其具体实现是在S域中利用谱模拟技术来拟合时变子波振幅谱,从而补偿由地层吸收所引起的振幅衰减;相位谱校正是消除子波剩余相位的影响,其具体实现是在S域中利用相位扫描来拾取随时间、空间和频率而变化的相位校正量,并由Parsimony准则来进行最佳相位判别。本文方法不需要直接求取Q值,能够适用于变Q值情况。理论模型和实际资料处理表明,该方法不仅能恢复地层反射系数的振幅谱,还可以有效消除子波剩余相位的影响,使子波接近或达到零相位,从而提高地震资料分辨率。     

粘弹各向异性反射体模型方位地震AVO模拟及分析（英文）

基于岩石物理模型和广义各向异性Zoeppritz方法在频率域计算裂缝型反射体模型反射波方位地震AVO响应。反射体模型为粘弹各向异性、有限厚度的地质体,其地震反射波形序列包含如下动力学信息,即分界面处介质的波阻抗和非弹性差异、反射体内部波的各向异性传播、在传播路径上的频散与衰减,以及来自顶底界面的反射波的调谐与干涉等。计算表明,速度频散和衰减增顶界面反射波大入射角反射时的振幅,而减弱底界面反射振幅。对于固定入射角的方位地震方位地震响应,PP波反射特征表现为随方位角的增加反射波形序列延续时间变长,而PSV和PSH转换类型反射波的方位各向异性变化特征稳定且受储层厚度影响较小,表现为PSV波反射振幅随方位角增加而增加,PSH波在0°和90°方位无反射能量,在45°方位反射振幅最强。     

热弹性介质中波的一类反射问题的解

研究了热弹性波的一类反射问题,就热弹性波的两种基本形式求得一类直反射问题及一类斜反射问题的解。结果表明,热弹性波的反射系数、折射系数不仅依赖于介质的性质,还依赖于波的频率;热弹性波的复反射系数及复折射系数使其在界面两侧的相位和附加温度场都出现跃变。     

非均匀P-偏振电磁波在导电界面的类全反射横向偏移

利用非均匀P-偏振电磁波（电场平行于入射面）在导电界面反射系数所产生的附加相角导出了非均匀电磁波在导电介质界面的横向偏移，并给出了一个低频电磁波算例，绘制了横向偏移随入射角的变化曲线. 计算结果表明，入射角在相移常数临界角、衰减常数临界角和90°处，横向偏移曲线存在三个间断点；当入射角等于这三个角时，电磁波将沿界面传播；当入射角在这三个角附近时，横向偏移效应影响较大；在其他角度入射时横向偏移与波长在一个数量级. 论文还讨论了横向偏移效应对电磁波测井测量结果所产生的误差，并给出了误差计算方法和算例.     

Frequency-dependent PP and PS reflection coefficients in fractured media

When a porous layer is permeated by mesoscale fractures, wave-induced fluid flow between pores and fractures can cause significant attenuation and dispersion of velocities and anisotropy parameters in the seismic frequency band. This intrinsic dispersion due to fracturing can create frequency-dependent reflection coefficients in the layered medium. In this study, we derive the frequency-dependent PP and PS reflection coefficients versus incidence angle in the fractured medium. We consider a two-layer vertical transverse isotropy model constituted by an elastic shale layer and an anelastic sand layer. Using Chapman's theory, we introduce the intrinsic dispersion due to fracturing in the sand layer. Based on the series coefficients that control the behaviour of velocity and anisotropy parameters in the fractured medium at low frequencies, we extend the conventional amplitude-versus-offset equations into frequency domain and derive frequency-dependent amplitude-versus-offset equations at the elastic–anelastic surface. Increase in fracture length or fracture density can enlarge the frequency dependence of amplitude-versus-offset attributes of PP and PS waves. Also, the frequency dependence of magnitude and phase angle of PP and PS reflection coefficients increases as fracture length or fracture density increases. Amplitude-versus-offset type of PP and PS reflection varies with fracture parameters and frequency. What is more, fracture length shows little impact on the frequency-dependent critical phase angle, while the frequency dependence of the critical phase angle increases with fracture density.     

非均匀电磁波在导电媒质界面反射的横向偏移

由电磁场边值关系给出了非均匀电磁波在导电媒质界面反射时反射系数所产生的附加相角. 利用这一附加相角导出了非均匀电磁波在导电介质界面的横向偏移,并进行了横向偏移的相关计算,绘出了横向偏移随入射角的变化曲线. 结果表明：在导电媒质界面反射电磁波的横向偏移随入射角的增大而增大,当入射角接近90°时,电磁波在界面要传播较长时间后才返回第一种媒质. 在同一入射角电场偏振化方向在入射面的电磁波要比电场偏振化方向垂直于入射面的电磁波的横向偏移大,随着电磁波频率的增加横向偏移变小.     

A seismic reflection from isotropic‐fractured fluid‐saturated layer

Average elastic properties of a fluid‐saturated fractured rock are discussed in association with the extremely slow and dispersive Krauklis wave propagation within individual fractures. The presence of the Krauklis wave increases P‐wave velocity dispersion and attenuation with decreasing frequency. Different laws (exponential, power, fractal, and gamma laws) of distribution of the fracture length within the rock show more velocity dispersion and attenuation of the P‐wave for greater fracture density, particularly at low seismic frequencies. The results exhibit a remarkable difference in the P‐wave reflection coefficient for frequency and angular dependency from the fractured layer in comparison with the homogeneous layer. The biggest variation in behaviour of the reflection coefficient versus incident angle is observed at low seismic frequencies. The proposed approach and results of calculations allow an interpretation of abnormal velocity dispersion, high attenuation, and special behaviour of reflection coefficients versus frequency and angle of incidence as the indicators of fractures.     

PKPdif波-内核低速层存在的地震学证据

通过对中国数字地震仪台网(CDSN)11个台1993—2012年间30个极远震记录的分析,识别出了PKP波入射到内外核界面(ICB)上的衍射波PKPdif波。PKPdif波在震中距120°左右时出现在PKIKP波之前,在震中距150°以后出现在PKIKP波之后,是一个长周期波。为了解释PKPdif波超前于PKIKP波的原因,设想在距地面约5 156.1～5 372.2 km的深度,即内外核界面下有可能存在一个PKIKP波的低速层(厚度约216.1 km)。该设想符合Jeffreys速度模型,给出的PKPdif波在震中距119.4°～176.1°间的走时表填补了目前使用的《IASPEI1991地震波走时表》的空白。讨论PKPdif波的运动学特征有助于对内外核界面物理性质的认识,有助于提高分析震相的水平和积累震相分析经验。     

Coupling between waveguide modes and field line resonances

WKBJ methods are often used to study the excitation of waveguide modes and field line resonances in the magnetosphere. In this paper, these methods are used to study the nature of the reflection and transmission process at a turning point when conditions are favourable for strong excitation of the field line resonance. The accuracy and region of validity of such WKBJ solutions are discussed. In regions where they are not valid, a series solution of the relevant equations is given. The wave fields can be found to great accuracy by matching WKBJ solutions across the turning point and resonance using this series solution. This allows the calculation of the Stokes constant which does not show Airy function behaviour as often assumed. The Stokes constant is effectively a reflection coefficient referred to the turning point. Its phase, when the transmission to the resonance is strong, is nearer to 180° than 90° as often assumed. Its magnitude allows the fraction of incident energy which is transmitted to the resonance to be calculated. These results are expected to be useful in studying the behaviour of waveguide modes.     

NOISE,TEMPERATURE COEFFICIENT,AND LONG TIME STABILITY OF ELECTRODES FOR TELLURIC OBSERVATIONS*

Numerous electrodes, already used in geophysics or just perfected by us, have been compared by measuring the three main characteristics which interest the user: noise spectrum, temperature coefficient and polarization with its stability versus time. Among the most used unpolarizable electrodes, silver-silver chloride (Ag-AgCl) are the best ones. But a systematic research of all different possible metal-salt couples, have led us to use lead-lead chloride (Pb-PbCl₂) for the following reasons: noise as low as the one of Ag-AgCl at 1 Hz and even lower for the low frequencies (0.4 μV at 1 Hz and 1.2 μV at 0.01 Hz for peak to peak value and ΔF=F), temperature coefficient about ten times weaker (?40 μV/°C instead of ?450 μV/°C) and also better long time stability of the polarization (1 mV/month instead of 2 at 10 mV/month). We have been using these electrodes since 1977 as “tube” electrodes which are very easy to use. They allow us to record correctly the fast variations thanks to their low noise, the very slow variations, their low temperature coefficient and their stability, and this with telluric lines only about 100 m long.     

A THEORY OF ACOUSTIC DIFFRACTORS APPLIED TO 2-D MODELS*

Finite-offset seismic reflection modeling of acoustic waves, propagating in a two-dimensional depth section of arbitrary complexity, is discussed. The procedure developed employs the principles of simplified (far-field) diffractor theory and ray tracing. Each reflector is represented by a set of discrete secondary sources or diffractors and the wavefield associated with each diffractor is calculated directly in the time domain by ray tracing. Reflections and diffractions are subsequently built up by the numerical superposition of these wavefields. This superposition is nondispersive for all frequencies for which the Fresnel zones are large compared with the diffractor separation. All primary travel paths connecting the shot to diffractor and diffractor to geophone are accounted for together with phase changes induced by focal events. The method allows the modeling of arbitrary trace gathers for energy originating from selected reflectors. The nonsequential nature of the algorithm makes it suited to machines capable of carrying out many similar operations in parallel or concurrently. Diffractor theory also provides physical insight into wave scattering and focusing. In particular, the half-differential waveform associated with a line diffractor leads to an explanation of the 90° phase lead induced by a cylindrical focus and, similarly, the full differential waveform of a point diffractor can be used to explain the 180° phase shift induced by a point focus.     

非均匀P\|偏振电磁波在导电界面的反射系数曲线

基于非均匀电磁波在导电媒质中传播时其相移常数和振幅衰减常数方向的不一致性，利用电磁波在导电媒质界面的边界条件，导出了非均匀P\|偏振电磁波的反射系数. 反射系数随入射角的变化曲线显示：当电磁波由电导率大的介质射向电导率小的介质时，在相移常数临界角和衰减常数临界角附近存在峰值，且反射系数的数值小于1，这一结果与全反射光的结果有明显的差异.     

Numerical simulation of reservoir sediment and effects on hydro‐dynamic response of arch dams

Based on the dynamic theory for saturated porous media by Biot (Journal of the Acoustical Society of America 1956; 28 : 168–178), a numerical model is presented to analyse the reflection behaviours of reservoir sediment and compared with those from the visco‐elastic model. It is concluded that the two models give very similar results of reflection coefficient α within the frequency range of interest. Then, using the two models, the change of the reflection coefficients α with various sedimentation parameters and excitation frequencies are studied in detail. The results are further used in the analysis of response functions of hydro‐dynamic pressures on, and structural displacements of the Xiang Hong Dian arch dam, for which some results from a field vibration test are available. It appears that effects of water compressibility with sediment reflection on hydro‐dynamic pressures and structural response are not significant for this specific case. Copyright © 2001 John Wiley & Sons, Ltd.