Seismic Velocities And Anisotropy From High-Resolution Sonic Logs
Seismic Velocities And Anisotropy From High-Resolution Sonic Logs
复制标题
高分辨率声波测井的地震速度和各向异性
DOI：
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发表时间：
1988
期刊：
影响因子：
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通讯作者：
M. Schoenberg
中科院分区：
文献类型：
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作者：
K. Hsu;C. Esmersoy;M. Schoenberg
高分辨率声波测井可以在非常短的间隔内对地层慢度进行采样，通常显示出点与点之间的相当大的变化，指示与测井采样一样精细或比测井采样更精细的分层。对于地震波传播，这种精细分层的介质可以通过基于声波测井的每个数据点代表各向同性层的假设的适当平均方案由等效均匀横向各向同性（TI）介质表示。这种假设在有许多薄页岩剖面的地区是不成立的，但即使如此，我们也能得到等效介质中垂直纵波和横波慢度的正确值。除了高分辨率声波和密度测井在一个高变异性的部分段，我们显示计算长波长的纵波和横波慢度沿着与各向异性的估计，水平到垂直应力，和声波漂移曲线，即旅行时间的基础上平均慢度减去，由于综合声波慢度。这种漂移是正的，并且对于压缩波达到1.5 ps/ft的值，对于剪切波达到2.5 ps/ft的值。在存在比测井采样更精细的尺度的分层的情况下，或者在存在某些层（例如页岩）的强固有各向异性的情况下，基于层的各向同性的等效介质的各向异性将倾向于低估真实的各向异性。来自多分量、多偏移距VSP测量的数据将提供必要的非垂直信息，以构建与声波和地震观测最一致的缓慢变化的等效TI介质。根据这些数据，我们做了一些初步的假设：首先，地层是水平分层的，其次，井是垂直的，最后，地层在任何一点上都是各向同性的。因此，方位角的变化被忽略，我们正试图确定最好的横向各向同性（TI）的背景模型的地震尺度兼容的高分辨率测井数据。输入数据由压、横波声波慢波、bp、s1和密度p组成，其分辨率等于高分辨率声波测井的分辨率。为了了解更长的地震波在这种精细分层（与地震波长相比）介质中的波动行为，有必要计算适合数据的最佳TI介质。TI介质的特征在于五个独立的弹性模型，它们与应力和应变有关。在压缩符号中，垂直方向用23表示，TI固体的应力-应变关系可以写成
High resolution sonic logs can sample formation slownesses over very short intervals, often showing considerable variation from point to point, indicative of layering as fine as or finer than the log sampling. For seismic wave propagation, this finely layered medium may be represented by an equivalent homogeneous transversely isotropic (TI) medium by the appropriate averaging scheme based on the assumption that each data point of the sonic log is representative of an isotropic layer. This assumption is not warranted in a region with many thin shale sections, but even so we obtain correct values of vertical compressional and shear slowness in the equivalent medium. Alongside segments of high resolution sonic and density logs in a section of high variability, we show computed long wavelength compressional and shear slownesses along with estimates of the anisotropy, the horizontal to vertical stress, and the sonic drift curves, i.e. the travel time based on average slownesses minus that due to the integrated sonic slownesses. This drift is positive and attains values of up to 1.5 ps/ft for compressional waves and 2.5 ps/ft for shear waves. In the presence of layering at a scale finer than log sampling, or in the presence of strong intrinsic anisotropy of some layers (such as shales), the anisotropy of the eqnivalent medium based on isotropy of the layers will tend to underestimate the true anisotropy. Data from multi-component, multi-offset VSP measurements will provide the non-vertical information necessary to construct the slowly varying equivalent TI medium most consistent with sonic and seismic observations. data, we make some preliminary assumptions: first that the formation is horizontally stratified, second that the welIis vertical, and last that the formation at any point is isotropic. Thus azimuthal variations are ignored and we are attempting to determine the best transversely isotropic (TI) background model on the seismic scale compatible with high resolution log data. The input data consist of compressional and shear sonic slowneszes, bp and s,, and density p at a rezolution equal to that of high resolution sonic logs. To know the wave behavior of much longer seismic waves in such a finely layered (compared to the seismic wavelength) medium, it is necessary to compute the best TI medium that fits the data. A TI medium is characterized by five independent elastic modnli relating stress and strain. In condensed notation, with the vertical denoted by 23, the stress-strain relation of a TI solid may be written