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水平横向各向同性介质(HTI)是用来描述各向同性基质中垂向断裂最简单的方位各向异性模型。假设地下界面是横向均匀的;并且利用P波NMO速度至少在三个不同炮检方向上随测量的方位的椭圆变化,我们可以估算出HTI介质的三个关键参数:垂向速度、各向异性和对称轴的方位。这样的参数估算对2-D采集时测线之间的角度或3-D采集时的炮检方位以及反演过程使用的一组方位都比较敏感。尤其是估算方位时的精度对于各向异性的强度很敏感,而在求解垂向速度和各向异性时的精度对于任何各向异性的强度大约都是相同的。为了使估算参数时的精度和稳定性达到最佳,当仅利用三个方向时,最好使炮检方向上的方位相隔60°。这种要求在可以设计成宽方位覆盖范围的陆上地震采集中是可行的。然而,在海上拖缆采集中,方位方向的数据覆盖受到限制。在海上拖缆测量中为了获得如此宽的方位覆盖范围,需要多个测量方向。为了利用60°间隔的三个方位方向完成反演,被方位各向异性盖层覆盖的一种HTI层相对于总时间而言应具有一个时间厚度,它至少等于NMO(叠加)速度误差与HTI层的层间各向异性强度之比。但是,当利用了多于三个炮检方向上的方位时(即全方位覆盖),它提供了一个能提高估算质量的有用数据的冗余度,因此,在较小的相对厚度上也能提供满意的参数估算。
Horizontally horizontal isotropic media (HTI) is the easiest azimuthal anisotropy model used to describe vertical fractures in isotropic matrices. Assuming that the subsurface interface is laterally uniform; and utilizing the elliptical variation of the P-wave NMO velocity with the measured azimuth in at least three different shotguns directions, we can estimate the three key parameters of the HTI media: vertical velocity, anisotropy And the axis of symmetry. This parameter estimation is more sensitive to the angle between the survey lines during 2-D acquisition or to the acquisition position during 3-D acquisition and to a set of orientations used in the inversion process. In particular, the accuracy in estimating the azimuth is very sensitive to the anisotropy and the accuracy in solving the vertical velocity and anisotropy is about the same for any anisotropy. In order to optimize the accuracy and stability in estimating the parameters, it is best to have the azimuths in the gun direction 60 ° apart when only three directions are used. This requirement is feasible in onshore seismic acquisition that can be designed to cover wide azimuths. However, azimuth data coverage is limited in maritime streamer acquisition. In order to obtain such a wide range of azimuth coverage at sea streamer measurements, multiple measurement directions are required. In order to perform inversion using three azimuthal directions at 60 ° intervals, an HTI layer covered by an azimuthal anisotropy should have a time thickness relative to the total time that is at least equal to the difference between the NMO (superposition) velocity error and the HTI The ratio of the anisotropy of the layers. However, it provides redundancy in useful data that improves the quality of estimates when more than three azimuths in the gun-cutting direction are exploited (ie, omnidirectional coverage), and therefore at lower relative thicknesses Provide satisfactory parameter estimation.