碳酸盐岩溶洞的“串珠”状地震反射特征形成机理研究

Formation mechanism research for bead-like seismic reflection of carbonate caves

本文采用一阶双曲型标量波动方程交错网格高阶有限差分法对薄层与溶洞的地震响应进行二维地震正演模拟,认为"串珠"状反射特征是溶洞顶、底反射以及微弱的溶洞顶、底间二次反射在偏移剖面上的响应;以塔里木哈拉哈塘海相碳酸盐岩实际地层参数为依据,设计了一个简化的水平层状地震地质模型(速度模型),通过三维地震物理模拟技术,对溶洞地震响应的瞬时振幅、均方根振幅、分频振幅和纵波阻抗体等四种属性进行了三维雕刻,得到了一种雕刻体积和真实体积的实验统计关系,认为前三种属性都将原本离散的"串珠"状转换成了连续的锥状振幅体,同时降低了纵向分辨率,而纵波阻抗剖面的纵向分辨率明显较其他属性剖面高。最后,针对各种属性剖面中存在的一些问题进行了讨论。

Using high-order staggering-grid finite difference method to solve the one-way hyperbolic scalar wave equation in inhomogeneous medium,we perform a 2D seismic forward modeling for caves and thin beds.The forward modeling reveals that the bead-like seismic reflection is the integrated response of cave's top reflection,cave's bottom reflection and faint multiple between cave's top and bottom in migrated profiles.In addition,according to the practical parameters of Halahatang marine carbonate reservoirs in Tarim Basin,a simplified layered physical model is constructed and the 3D physical simulating technology is performed on this model.The empirical relationship between attribute depiction volume and actual volume is obtained after analyzing the four attributes of caves' seismic responses,including instantaneous amplitude,RMS amplitude,monochromatic amplitude and P-wave impedance.Further study shows that the first three attributes transform discrete 'beads' into continuous cone-shaped amplitude body and destruct the vertical resolution,while the P-wave impedance has a better vertical resolution.At last,some attributes in these profiles are discussed.