多测线变偏移距VSP地震各向异性反演

本文从一般弱各向异性介质参数反演中得到了使用两条相互正交的变偏VSP测线计算弱各向异性(WA)参数的反演公式. 如果仅仅使用qP波, 则可以确定9个独立的WA参数, 这9个WA参数可以完全地描述井中接收点在两个剖面内介质的各向异性性质. 通过对走时曲线进行最小二乘条件下的三次样条光滑, 可以获得慢度矢量的垂直分量和水平分量. 如果介质是横向非均匀介质, 则水平分量仅仅被用作反演时的约束条件. 为了获得偏振矢量, 本文引入质心计算方法, 该方法计算简单、 稳定, 而且不存在解的奇异问题. 在寻找与一般各向异性介质最接近的高对称性正交各向异性介质和TTI各向异性介质时, 使用qP波各向异性坐标变换方法和最小二乘求解方法, 得到了与一般各向异性介质最接近的正交各向异性和TTI各向异性参数及其对称轴方向参数的计算公式. 使用这些方法, 对瓜哇海地区布设的两条相互正交的变偏VSP测线数据进行各向异性反演, 获得了井中10个接收点处介质的WA参数. 数值计算和实际资料反演表明, 本文所使用的反演方法能够准确地得到VSP井中接收点处介质的WA参数, 这是地震勘探中研究地壳介质各向异性性质最直接和最可靠的方法.      

Joint interferometric imaging of walkaway VSP data

In this paper, we image the subsurface reflectors by interferometric imaging using primary and downgoing first-order free-surface related multiple reflections in walkaway VSP data. By analyzing the stack fold distribution, we find that primary-direct interferometric imaging has a smaller image range, but its stack fold is higher near the well while ghost-direct interferometric imaging is the opposite. We try to solve this problem by the joint interferometric imaging of walkaway VSP data, combining primary-direct interferometric imaging with ghost-direct interferometric imaging. In this way, we can effectively widen the imaging range, simultaneously increase the fold (especially near the well), suppress spurious interference, and improve the image SNR, so that we can get a more credible image. Test results on synthetic walkaway VSP data and field data show that joint interferometric imaging is very effective.     

Amplitude Variation with Offset Responses Modeling Study of Walkaway Vertical Seismic Profile Data at CO2 Geological Storage Site, Ketzin, Germany

An important component of any CO2 sequestration project is seismic monitoring for tracking changes in subsurface physical properties, such as velocity and density. Different reservoirs have different amplitude variation with offset (AVO) responses, which can define underground conditions. In the present paper we investigate walkaway vertical seismic profile (VSP) AVO response to CO2 injection at the Ketzin site, the first European onshore CO2 sequestration pilot study dealing with research on geological storage of CO2. First, we performed rock physics analysis to evaluate the effect of injected CO2 on seismic velocity using the Biot-Gassmann equation. On the basis of this model, the seismic response for different CO2 injection saturation was studied using ray tracing modeling. We then created synthetic walkaway VSP data, which we then processed. In contrast, synthetic seismic traces were created from borehole data. Finally, we found that the amplitude of CO2 injected sand layer with different gas saturations were increased with the offset when compared with the original brine target layer. This is the typical class III AVO anomaly for gas sand layer. The AVO responses matched the synthetic seismic traces very well. Therefore, walkaway VSP AVO response can monitor CO2 distribution in the Ketzin area.     

变偏移距VSP射线追踪模型

变偏移距ＶＳＰ方法以其独特观测方式及解决地质问题的能力而倍受人们关注。变偏移距ＶＳＰ正演模型是理论研究、波场识别的得力工具。本文以射线理论为基础,研制了变偏移距ＶＳＰ射线追踪模型程序,它既可以单独模拟Ｐ波、Ｓ波,也可以模拟Ｐ、Ｐ－ＳＶ波的复合波场,可以适应复杂介质情况。给出的几个例子,说明本方法具有快速、灵活、实用的特点。     

Local Determination of Weak Anisotropy Parameters from Walkaway VSP qP-Wave Data in the Java Sea Region

We apply the inversion scheme of Zheng and Peník (2002) to the walkaway VSP data of Horne and Leaney (2000) collected in the Java Sea region. The goal is a local determination of parameters of the medium surrounding the borehole receiver array. The inversion scheme is based on linearized equations expressing qP-wave slowness and polarization vectors in terms of weak anisotropy (WA) parameters. It thus represents an alternative approach to Horne and Leaney (2000), who based their procedure on inversion of the Christoffel equation using a global optimization method. The presented inversion scheme is independent of structural complexities in the overburden and of the orientation of the borehole. The inverson formula is local, and has therefore potential to separate effects of anisotropy from effects of inhomogeneity. The data used are components of the slowness vector along the receiver array and polarization vectors. The inversion is performed without any assumptions concerning the remaining components of the slowness vector. The inversion is made (a) assuming arbitrary anisotropy, i.e., without any assumptions about symmetry of the medium, (b) assuming transverse isotropy with a vertical axis of symmetry and (c) assuming isotropy of the medium. Inverted are the raw data as well as data, in which weighting is used to reduce the effect of outliers. It is found that the WA parameters _z, ₁₅ and ₃₅ are considerably more stable than the parameters _x and _x. The latter two parameters are also found to be strongly correlated. Weaker correlation is also found between the mentioned two parameters and _z. The results of inversion show clearly that the studied medium is not isotropic. They also seem to indicate that the studied medium does not possess the VTI symmetry.     

高分辨率多方位VSP方法在塔河油田奥陶系裂缝性储层研究中的应用

塔河油田奥陶系碳酸盐岩储层的裂缝及缝洞非常发育，在纵横向都表现出很强的非均质性。常规地面地震方法难以精确地应用于该区的储层预测。将高分辨率多方位VSP地震方法应用于塔河油田储层描述，实现了上行反射P波和S波精确成像，提高了地震资料及储层预测的分辨率；并建立了含缝洞碳酸盐岩储层的地震反射特征和裂缝发育储层的地震识别方法。     

Walkaway VSP数据的联合相干成像(英文)

本文将相干成像用于WVSP数据的一次反射波和下行地表多次波的成像中,通过对叠加次数分布的分析,发现一次反射波相干成像的成像范围小但在井位置处的叠加次数高;下行地表多次波相干成像的成像范围大而在井位置处的叠加次数少。基于此,本文尝试利用一种WVSP的联合相干成像方法来解决这一问题。该方法利用WVSP的直达波与下行地表多次波和直达波与一次反射波来进行联合相干成像。这种联合相干成像方法在有效拓宽成像面积的同时增加了覆盖次数(特别是在井旁),使干涉记录中的虚假同相轴得到了有效地压制,提高了成像剖面的信噪比,使成像结果更加可靠。正演模拟得到的WVSP合成记录和野外实际采集到的WVSP数据处理结果均表明这种方法的有效性。     

变井源距垂直地震剖面各向异性参数反演

利用微扰理论推导了弱各向异性(WA)介质参数正反演计算的基本公式;给出了在已知慢度矢量的一个分量和偏振矢量情况下确定WA参数的方法.如果这一方法被用于单一的变井源距垂直地震剖面(walkawayVSP)资料,可以获得9个WA参数.这9个WA参数完全决定了qP波和两个qS波在由剖面和钻井所决定的平面内传播的特性.对单条walkawayVSP观测系统数据的产生和WA参数的反演进行了数值模拟计算,对所能确定的WA参数及其可靠性进行了详细的讨论.