基于互相关目标函数的一阶表面多次波反演成像方法研究

The subsurface salt body is a good covering layer of oil reservoir, which is a possible tectonic zone to find large oilfield in deep sea. As primaries reflected beneath the salt are hard to be received, it is a severe challenge for the conventional seismic migration of primaries in imaging areas beneath the salt. Different with primaries, surface-related multiples travel through the salt body several times with small reflection angles, which can be used to improve the illumination of the oil reservoir beneath the salt. However, migration of surface-related multiples would also generate many cross-talks which are hard to be eliminated. Thus, in this project, we plan to develop a new inversion imaging method of surface-related multiples, which is efficient and can remove cross-talks very effectively. To reduce the cross-talks with other multiple events of different orders, this method isolates first-order surface-related multiples for imaging. The correlative least-squares reverse time migration is then used to image first-order surface related multiples, which can suppress cross-talks from first-order multiple events and improve the imaging resolution even when the data are from complex subsurface and are low in quality. With combining the random-phase based multi-source scheme with a preconditioner of structure-enhancing smoothing filter to promote the noise removal, the inversion imaging of first-order multiples can be calculated more efficiently. We can finally build a migration method of surface-related multiples, which can provide images with high signal-to-noise ratio and high resolution for the large-scale marine oil and gas exploration.

地下盐体是有利的油藏覆盖层，是可能发现深海大油田的构造区。由于盐体以下的一次反射波常常无法接收，利用一次反射波的传统地震偏移方法在盐下成像上面临着严峻挑战。不同于一次反射波，表面多次反射波以小角度多次穿过盐体，用其可提高盐下油气藏的照明度；但表面多次波成像同时会产生大量极难消除的噪声。因此，本项目拟发展一种兼具强抗噪能力和高计算效率的表面多次波反演成像方法。该方法仅提取一阶表面多次波进行成像，减少不同阶地震波场相互串扰产生的假象。采用互相关型最小二乘逆时偏移反演成像方法，在复杂介质和非理想采集数据情况下，依然能够压制一阶表面多次波成像中的噪声并提高成像分辨率；引入随机相位编码的多炮记录偏移思想，并以结构增强平滑滤波器作为加速去噪的预条件算子，提高计算效率。最终建立一种能够为海上大规模油气勘探提供高信噪比、高分辨率成像结果的表面多次波成像方法。

地下盐体是有利的油藏覆盖层，是可能发现深海大油田的构造区；然而也是我们传统成像的盲区。由于盐体以下的一次反射波常常无法接收，利用一次反射波的传统地震偏移方法在盐下成像上面临着严峻挑战。相比之下，表面多次反射波以小角度多次穿过盐体，对盐下油气藏有更高的照明度。表面多次波成像的挑战是极难消除的串扰噪声会降低成像信噪比。为了解决上述问题，本项目发展了一种兼具强抗噪能力和高计算效率的表面多次波反演成像方法。采用互相关型最小二乘逆时偏移反演成像方法该方法对提取的一阶表面多次波成像，能够非常强健的压制成像噪声并提高成像分辨率。进一步地，利用随机相位编码算法的提高计算效率。最终我们建立了一种能够为海上大规模油气勘探提供高信噪比、高分辨率成像结果的快速表面多次波成像方法。我们的研究成果得到了国内外同行的充分认可。以该项目为第一资助项目，项目负责人及其合作者已经在勘探地球物理国际权威期刊《Geophysics》和《Geophysical Journal International》上共计发表了3篇文章，其中一篇文章被美国勘探地球物理学会（SEG）主办的向石油工业界科普最新进展的期刊The Leading Edge选为研究亮点（Bright Spots）并引用文章图片。相关研究成果被选为2018年度中国科学院地质与地球物理研究所十大优秀科技成果。