基于精细积分法的三维弹性波数值模拟(英文)

波动方程有限差分法是地震数值模拟中的一种重要的方法,对理解和分析地震传播规律、分析地震属性和解释地震资料有着非常重要的意义。但是有限差分法由于其离散化的思想,产生了不稳定性。精细积分法在有限差分法的基础上,在时间域采用解析解的表达形式,在空间域保留任意差分格式,发展成为半解析的数值方法。本文结合并发展了以往学者的成果,推导了任意精细积分法的三维弹性波正演模拟计算公式,并对其稳定性进行了数值分析。在计算实例中,实现了精细积分法二维和三维弹性波模型的地震正演模拟,对计算结果的分析表明,精细积分法反射信号走时准确,稳定性好,弹性波场相较于声波波场,弹性波波场成分更为丰富,包含了更多波型成分(PP-和PS-反射波、透射波和绕射波),这对实际地震资料的解释和储层分析有重要的意义。实践证明,该方法可直接应用到弹性波的地质模型的数值模拟中。     

Numerical simulation of seismic wave in elastic and viscoelastic TTI media*

Based on the two-dimensional (2D) three-component first-order velocity-stress equation, the high order staggered mesh finite difference numerical simulation method was used to simulate the elastic and viscoelastic tilted transversely isotropic (TTI) media. The perfect matched layer (PML) absorption boundary condition was selected to eliminate the boundary effect. The results show that: ① Under the condition of fixed elastic parameters of elastic TTI medium, when the polarization angle and azimuth are 60° and 45° respectively, the degree of shear wave splitting is significantly greater than the angle of 0°; ② The influence of viscoelasticity on TTI medium is mainly reflected in the amplitude. If the quality factor decreases, the attenuation of the seismic wave amplitude increases, causing the waveform to become wider and distorted. If the quality factor increases, the viscoelastic medium becomes closer to elastic medium; ③ For TTI medium with different polarization angle and azimuth angle in the upper and lower layers, the shear wave can multiple splits at the interface of medium. The symmetry of seismograms is affected by the polarization angle and azimuth angle of TTI medium; ④ Viscoelasticity has a great influence on reflected wave, transmitted wave and converted wave in the low-velocity model. When the viscoelasticity is strong, the weaker waves may not be shown.     

Numerical analysis of seismic wave propagation in fluid-saturated porous multifractured media

Elastic wave propagation and attenuation in porous rock layers with oriented sets of fractures, especially in carbonate reservoirs, are anisotropic owing to fracture sealing, fracture size, fracture density, filling fluid, and fracture strike orientation. To address this problem, we adopt the Chapman effective medium model and carry out numerical experiments to assess the variation in P-wave velocity and attenuation, and the shear-wave splitting anisotropy with the frequency and azimuth of the incident wave. The results suggest that velocity, attenuation, and anisotropy vary as function of azimuth and frequency. The azimuths of the minimum attenuation and maximum P-wave velocity are nearly coincident with the average strike of the two sets of open fractures. P-wave velocity is greater in sealed fractures than open fractures, whereas the attenuation of energy and anisotropy is stronger in open fractures than sealed fractures. For fractures of different sizes, the maximum velocity together with the minimum attenuation correspond to the average orientation of the fracture sets. Small fractures affect the wave propagation less. Azimuth-dependent anisotropy is low and varies more than the other attributes. Fracture density strongly affects the P-wave velocity, attenuation, and shear-wave anisotropy. The attenuation is more sensitive to the variation of fracture size than that of velocity and anisotropy. In the seismic frequency band, the effect of oil and gas saturation on attenuation is very different from that for brine saturation and varies weakly over azimuth. It is demonstrated that for two sets of fractures with the same density, the fast shear-wave polarization angle is almost linearly related with the orientation of one of the fracture sets.     

黏弹性EDA介质中地震波的衰减特性研究

本文首先由Christoffel方程推导出黏弹性EDA介质中均匀、 非均匀P波、 SV波和SH波的相速度表达式, 然后参照极端各向异性介质的相关计算方法, 推导出EDA介质中均匀、 非均匀地震波相衰减系数和群衰减系数的表达式, 并通过数值计算分析了相速度、 相衰减系数、 群衰减系数与裂隙方位的关系. 结果表明: 均匀介质中SH波的相速度和相衰减系数均可指示裂隙的走向; 非均匀介质中SH波相衰减系数随非均匀角的增大而增大, 且其对称轴与介质对称轴的夹角也相应增加; 由于地震波振幅的衰减随岩石物理性质的变化比地震波速度的变化更为灵敏, 而且携带了更多的岩石物理性质信息, 因此可用来探明裂隙走向、 密度及含水特性, 进而应用于预测、 预防地下工程地质灾害事故.      

Modelling the wave phenomena in acoustic and elastic media with sharp variations of physical properties using the grid‐characteristic method

This paper introduces a novel method of modelling acoustic and elastic wave propagation in inhomogeneous media with sharp variations of physical properties based on the recently developed grid‐characteristic method which considers different types of waves generated in inhomogeneous linear‐elastic media (e.g., longitudinal, transverse, Stoneley, Rayleigh, scattered PP‐, SS‐waves, and converted PS‐ and SP‐waves). In the framework of this method, the problem of solving acoustic or elastic wave equations is reduced to the interpolation of the solutions, determined at earlier time, thus avoiding a direct solution of the large systems of linear equations required by the FD or FE methods. We apply the grid‐characteristic method to compare wave phenomena computed using the acoustic and elastic wave equations in geological medium containing a hydrocarbon reservoir or a fracture zone. The results of this study demonstrate that the developed algorithm can be used as an effective technique for modelling wave phenomena in the models containing hydrocarbon reservoir and/or the fracture zones, which are important targets of seismic exploration.     

高频电磁波在不同目标体上反射图像特征研究

针对高频电磁波技术在北京勘察设计行业应用的空白,本次研究利用探地雷达技术对北京地区典型工程目标体进行了研究.针对不同的地下目标体对高频电磁波所反映出的不同反射特性,总结出一些图像特征规律.通过建立对各类雷达探测图像进行地质解释的理论依据和基础,本次研究对层状介质、地下管道、CFG桩、碎石夯扩桩、水泥土桩和洞穴等目标体的雷达图像特征进行了较系统的研究和总结,为今后日常的检测工作奠定了很好的基础.     

Kirchhoff积分叠前时间偏移全方位角度道集生成方法与实现

方位角度域共成像点道集能够客观反映地下介质的速度、各向异性参数异常以及振幅随角度变化（AVA）和裂缝信息。传统Kirchhoff PSTM通常输出偏移距域共成像点道集,对于速度分析、各向异性分析、AVA分析、裂缝识别等均存在诸多不便。本文提出了基于走时梯度的Kirchhoff叠前时间偏移全方位角度集输出方法并提出工业上切实可行的实现方案。通过走时场梯度计算波场传播方向矢量,形成能够反映观测系统参数和波场传播情况的全方位角度域共成像点道集。为了在大规模地震数据Kirchhoff积分叠前时间偏移中输出全方位角度道集,本文给出基于输入道方式的偏移实现方法,采用逐条inline线进行线偏移成像,从而大大降低了全方位角度道集输出对计算机内存的压力,显著提高了Kirchhoff积分时间偏移输出全方位角度道集的可行性。三维盐丘模型测试和海上某区块三维实际资料试验证明了本文方法的正确性。      

TTI介质各向异性参数多波反演与PS波AVO分析

把遗传算法引入到了TTI介质AVO信息反演各向异性参数的过程中,依据TTI介质PP波、PS波反射系数公式,建立Thomsen参数和TTI介质对称轴倾角、方位角的目标函数,分别通过PP波和PS波的反射系数反演出了各向异性参数和对称轴倾角、方位角等信息.文中对反演结果的精确度和稳定性进行了分析,发现PS波的反演结果优于PP波反演结果;对称轴倾角的反演准确性明显优于对称轴方位角.本文通过模型正演合理解释了这一现象的原因.最后,本文通过对PS波AVO梯度的研究,提出了利用PS波振幅定性分析TTI介质对称轴倾角的方法.     

川西凹陷孝泉地区3D3C量地震资料采集方法

川西坳陷孝泉地区深层须家河组致密砂岩气藏属于典型非常规裂缝性气藏,储层识别、裂缝检测、含气性识别是气藏研究的重点和难点.转换波3D3C勘探可同时获得反映岩石骨架和各向异性特性的C波资料及反映骨架及流体特性的P波资料,因而适用于川西孝泉深层超致密裂缝性气藏.在3D3C地震勘探中,三维三分量地震采集方法是采集到高质量多分量原始资料的技术保障,本文重点研究这种采集方法.首先根据地球物理参数,结合地质任务要求,分析了三维三分量观测系统设计的方法及观测系统参数,然后根据分析结果和勘探目的层的实际情况设计了同时适合纵波勘探和转换波勘探的面元尺寸、最大和最小炮检距、接收线距、束间滚动距等参数并确定了三维三分量观测系统.该观测系统在孝泉地区资料采集中,获得的三分量资料波组特征清楚,同相轴连续,反射信息丰富;Z分量剖面和R分量剖面反射层次清楚,目的层反射特征明显,具有非常好的构造形态一致性.     

P- and S-wavefield simulations using both the first- and second-order separated wave equations through a high-order staggered grid finite-difference method

In seismic exploration, it is common practice to separate the P-wavefield from the S-wavefield by the elastic wavefield decomposition technique, for imaging purposes. However, it is sometimes difficult to achieve this, especially when the velocity field is complex. A useful approach in multi-component analysis and modeling is to directly solve the elastic wave equations for the pure P- or S-wavefields, referred as the separate elastic wave equations. In this study, we compare two kinds of such wave equations: the first-order (velocity–stress) and the second-order (displacement–stress) separate elastic wave equations, with the first-order (velocity–stress) and the second-order (displacement–stress) full (or mixed) elastic wave equations using a high-order staggered grid finite-difference method. Comparisons are given of wavefield snapshots, common-source gather seismic sections, and individual synthetic seismogram. The simulation tests show that equivalent results can be obtained, regardless of whether the first-order or second-order separate elastic wave equations are used for obtaining the pure P- or S-wavefield. The stacked pure P- and S-wavefields are equal to the mixed wave fields calculated using the corresponding first-order or second-order full elastic wave equations. These mixed equations are computationally slightly less expensive than solving the separate equations. The attraction of the separate equations is that they achieve separated P- and S-wavefields which can be used to test the efficacy of wave decomposition procedures in multi-component processing. The second-order separate elastic wave equations are a good choice because they offer information on the pure P-wave or S-wave displacements.     

Rayleigh wave separation using high-resolution time-frequency polarization filter

Obtaining geological information from seismic data motivates researchers to innovate and improve seismic wave processing tools. Polarization-based methods have received much attention regarding their ability to discriminate between different phases of the seismic wave based on polarity. Combining the intuitive definition of polarity in the frequency domain (monochromatic waves) with the non-stationary properties provided by time-domain methods, time-frequency approaches are attracting widespread interest because they localize the information extracted from the seismic waves in the joint time and frequency domains. Due to the lack of high-resolution time-frequency maps, the time-frequency polarization approach was not able to resolve specific temporal polarity changes in the seismic signal. The main objective of this study was to devise a robust time-frequency-based polarization filtering method using high-resolution polarization attributes obtained directly from the sparse time-frequency map without using Eigen analysis or analytic signals. The method proposed here utilizes a computationally effective sparsity-based adaptive S-transform to obtain a high-resolution polarization map of an inherently non-stationary seismogram for the entire frequency content of the signal at different times. The superiority of the proposed method over the S-transform method was verified using synthetic and real data sets to calculate the polarization attributes in the time-frequency domain and separate the Rayleigh waves from the seismogram.     

中海油多分量地震处理技术的发展与应用实例

20世纪末中海油在南海油气勘探中成功试验了二维多分量地震技术.其后十多年,中海油进一步在不同近海油气盆地采集了三维多分量OBC地震资料.但由于针对三维转换波的处理未能形成有效的关键技术,除双检叠加利用了水压分量和陆检垂直分量外,大量水平分量数据未被使用.鉴于此,中海油在十二五期间开展三维多分量地震数据处理的关键技术攻关：针对弹性波场的矢量特征、转换波射线路径不对称以及双程旅行时多时间尺度等问题,成功研发了矢量化的信号处理技术、弹性波速度建模以及叠前时间偏移成像等技术;集成了相对完善的三维弹性波成像EWI软件系统;完成了多个试验区的三维四分量OBC地震转换波的处理,取得了好于以往技术的效果;建立了海上多分量OBC地震资料处理流程.但相对于成熟的纵波处理技术,海洋多分量地震处理技术仍需要不断完善与发展.     

基于反射系数谱理论的薄层多波AVO

AVO分析是目前地震勘探潜在油气储层的一个重要方法。体散射信息包含了层结构、岩性和孔隙流体信息,对地震勘探非常有用。但是基于 Zoeppritz方程的传统AVO分析之只包含了单层信息。薄层厚度定量解释对构造解释、储层描述和储层横向预测都非常重要。本文阐述的基于频率域弹性传播矩阵反射系数谱方法既考虑了层界面引起的振幅变化(Zoeppritz方程),也考虑了层内传播引起的振幅变化。因此该反射系数谱既包括单一层界面信息,也包括层内体散射信息。该反射系数谱是层厚和频率的连续函数,便于分析频率和层厚对反射系数谱的影响。可分析的薄层厚度可以无限小,直至消失。可分析的频率是任意的和连续的。这是对时间域反射系数做傅里叶变换无法实现的。地震波的传播是复杂的,各种波型是同时存在而且相互转换的,该反射系数谱考虑了各种波型在传播过程中的相互转换以及多次波。与比射线方法比更便于正演薄层多波多分量AVO响应。     

Reconstruction of the layer anisotropic elastic parameters and high-resolution fracture characterization from P-wave data: a case study using seismic inversion and Bayesian rock physics parameter estimation

Wide-azimuth seismic data can be used to derive anisotropic parameters on the subsurface by observing variation in subsurface seismic response along different azimuths. Layer-based high-resolution estimates of components of the subsurface anisotropic elastic tensor can be reconstructed by using wide-azimuth P-wave data by combining the kinematic information derived from anisotropic velocity analysis with dynamic information obtained from amplitude versus angle and azimuth analysis of wide-azimuth seismic data. Interval P-impedance, S-impedance and anisotropic parameters associated with anisotropic fracture media are being reconstructed using linearized analysis assuming horizontal transverse anisotropy symmetry. In this paper it is shown how additional assumptions, such as the rock model, can be used to reduce the degrees of freedom in the estimation problem and recover all five anisotropic parameters. Because the use of a rock model is needed, the derived elastic parameters are consistent with the rock model and are used to infer fractured rock properties using stochastic rock physics inversion. The inversion is based on stochastic rock physics modelling and maximum a posteriori estimate of both porosity and crack density parameters associated with the observed elastic parameters derived from both velocity and amplitude versus angle and azimuth analysis. While the focus of this study is on the use of P-wave reflection data, we also show how additional information such as shear wave splitting and/or anisotropic well log data can reduce the assumptions needed to derive elastic parameter and rock properties.     

Propagation characteristics of converted refracted wave and its application in static correction of converted wave

Three-component seismic exploration through P-wave source and three-component geophone is an effective technique used in complicated reservoir exploration. In three-component seismic exploration data processing,one of the difficulties is static correction of converted wave. This paper analyzes propagation characteristics of non-converted and converted refracted waves,and discovers a favor-able condition for the formation of converted refracted wave,i.e. the velocity of overlaying medium S wave is much lower than that of underlying medium S wave. In addition,the paper proposes the static correction method of converted wave based on PPS converted refracted wave,and processes the real three-component seismic data with better results of static correction of converted wave.     

Obliquely incident wave propagation across rock joints with virtual wave source method

Due to the presence of joints, waves are greatly attenuated when propagating across rock masses. Zhu et al. (2011) (Normally incident wave propagation across a joint set with virtual wave source method. J. Appl. Geophys.73, 283–288.) studied normally incident wave propagation across a joint set with the virtual wave source method (VWSM). The introduced VWSM has merits in some aspects, especially the capability of separating differently arriving transmitted waves. However, normal wave incidence is only the special case for wave incidence with arbitrary incident angles. Obliquely incident wave propagation across a joint set is more complicated than normally incident wave propagation due to wave transformation at the joints. As a continuation of the previous paper, this work is extended to analytically study obliquely incident wave propagation across joints with VWSM. Complete theoretical reflection and transmission coefficients across single joint described by displacement discontinuity model are derived through plane wave analysis. The superposition of P wave and S wave is for the first time mathematically expressed and studied. The VWSM is verified through comparison with the propagation matrix method. Through extensive parametric studies on wave transmission across single and multiple parallel joints, it is shown that transmitted wave energy is mainly constrained in the transmitted wave of the same type as the incident wave. And with increasing joint stiffness, the transmission coefficients across single joint increases except those whose wave type is different from the incident wave. The amplitude of superposed transmitted wave for P wave incidence increases with incident angle, which is coincident with field observations. Both joint spacing and number of joints have significant effects on transmission coefficients. We find that when joint spacing is sufficiently large, the transmission coefficient is no longer a constant as the normally incident wave propagation case (Zhu et al., 2011). And when joints are very closely spaced, wave attenuation depends little on the number of joints, which is different from the conclusions from equivalent medium method.     

垂向裂隙各向异性煤层地震波响应

煤层中存在的裂隙会导致介质表现为各向异性,本文以HTI型煤层为例,结合各向异性介质弹性矩阵和各向异性裂隙理论,推导出不同充填物的垂直裂隙中各向异性参数表达式,将其应用于地震波响应分析;通过改进的交错网格差分法和各向异性Christoffel方程波场分解法,得到地震波合成记录和分解后的P波和SV波记录;将Thomsen群速度与相速度公式,经过坐标轴旋转变换,得到HTI型煤层中不同各向异性参数的地震波速度响应表达式;建立不同类型煤层地质模型,分析了裂隙密度、裂隙充填物以及煤层厚度等参数变化时的地震波响应特征.研究结果为分析垂向裂隙各向异性薄煤层地震波传播规律提供工具,为选用相应地震数据进行地震波各向异性参数反演提供依据.     

Separation of split shear waves based on a hodogram analysis of HTI media

Although the shear-wave birefringence phenomenon affects the imaging of converted shear waves, it also provides a considerable amount of information on subsurface fracture development. Therefore, it is significant to separate split shear waves before seismic interpretation and reservoir prediction. In this paper, we propose a new method of split shear waves separation based on the polarization directions derived from hodogram analysis. Through the hodogram analysis, we find that the split shear-wave particle motions are within the range of a specific and fixed rectangle, which have relations with the fracture azimuth in strata. In addition, we found that a couple of split shear waves can only be fitted to the unique trajectory rectangle through the theoretical derivation. Based on this, we establish the trajectory rectangle through the wave vector calculation and calculate the fracture azimuth according to the fact that the one edge of the trajectory rectangle is along or perpendicular to the fracture azimuth. Synthetic data analysis shows that the calculation accuracy of fracture azimuth under the constraint of trajectory rectangle is less affected by the time delay between split shear waves than using the method of eigenvector–eigenvalue decomposition (EED). Therefore, we can obtain better results for separation of split shear waves using our method than using EED. Eventually, we propose an approach of layer stripping to deal with the problem that shear wave split several times due to the situation that different strata have different fracture azimuths. Synthetic data test indicates that our method can achieve higher calculation efficiency and faster convergence speed than the conventional eigenvector–eigenvalue decomposition method, even though the data are of a low signal-to-noise ratio. Moreover, field data applications show the effectiveness and potential of our method.     

利用全方位P波属性进行裂缝检测的地震方法

胜利油田存在着一种特殊的裂隙性油气藏,即泥岩裂隙油气藏。由于该类裂隙储层的孔隙度很小,岩石物性参数变化不灵敏,并表现出很强的各向异性,因此,其勘探难度很大。到目前为止,国内外还没有一套成熟的地质、物探、测井及钻井等资料综合分析的裂隙方位、分布、密度的识别方法。本文在研究国外裂缝检测方法的基础上,提出了波阻抗随方位变化(IPVA)的新方法,结合罗家地区的泥岩裂隙地震地质特征,研究了利用多方位 P 波资料检测定向垂直裂缝的地震采集、处理和识别方法,对不同共中心点 CMP 位置的全方位 P 波资料在速度随方位变化(VVA)及振幅随方位角变化(RVA)研究的基础上,进行波阻抗随方位变化(IPVA)的研究,用于识别裂缝的分布、走向及密度。经罗家地区实际资料的应用,见到了初步的效果,证明该方法是潜力较大的高角度裂隙的定量检测方法。     

被动源面波和体波成像在内蒙古浅覆盖区勘探应用

地震勘探具有勘探深度和分辨率的优势,在矿产勘探中多被采用.但主动源反射地震具有成本高、在矿区采集困难等难题,限制了其广泛应用.无需主动源激发、利用天然噪声的被动源地震应用于勘探,可成为其低成本替代选项.本文在内蒙古浅覆盖区矿区进行了被动源勘探试验,采用相关计算获得拟炮集记录,并基于频率域信噪比计算,在生成拟炮集前实现了...