OVT域宽方位层析速度建模与深度域成像

Wide azimuth tomographic velocity model building and depth imaging in the OVT domain

叠前深度偏移常规速度建模技术,不能有效利用宽方位地震资料的方位角信息,导致速度模型精度不足,最终偏移结果不如预期。本文提出了一套在OVT域实现的宽方位层析速度建模技术流程。该方法利用CIP道集中的方位角信息,能反演出细微的小尺度速度变化,具有很高的精度和分辨率。通过OVT域宽方位层析反演得到的蝴蝶道集拉得较平,方位剩余时差得到消除,碳酸盐岩串珠成像质量明显改善。分析认为,这种方位剩余时差实际上主要是由储层的非均质性引起而不是由方位各向异性引起。研究表明,与常规速度建模技术和分扇区多方位层析技术相比,OVT域宽方位层析反演技术更灵活高效,能得到更高分辨率的速度模型,从而提高深度域成像质量。

Conventional velocity model building for prestack depth migration cannot take into consideration seismic azimuth information so that the final velocity model and depth imaging are not as good as expected.In order to take advantage of wide azimuth3 Dseismic data,we propose in this paper a wide azimuth tomography workflow in the OVT domain to build an earth model with great accuracy and details.This workflow can resolve small scale velocity changes using azimuth information from seismic data.Butterfly gathers through full azimuth inversion in the OVT domain are much better flattened.Not only azimuth moveout changes are almost disappeared,but also depth target(carbonate caves)imaging is greatly improved.From our analysis of the survey,we concluded that these azimuth moveout variations are primarily caused by overburden lateral velocity heterogeneity rather than potential azimuth velocity anisotropy.Compared with conventional model building approach and sector-based multi azimuth tomography,OVT-based wide azimuth tomography inversion is more efficient and flexible,and can obtain higher resolution velocity model and better depth imaging.