四川盆地复杂地表高精度建模技术及其应用

High-precision modeling for complex surface conditions and its application to Sichuan Basin

四川盆地地表地形起伏剧烈,岩性复杂多变,低降速带分布复杂,造成资料信噪比低,静校正问题突出。只有构建高精度的近地表结构,才能获得准确的静校正量,进而改善地震资料的成像效果。因此,利用小折射、微测井和大炮初至层析成果加权融合构建了近地表模型,并在建模过程中,纵横向都针对性地进行加权融合。结果表明:①双向加权融合法建模可以较真实刻画近地表低降速层的结构,所获得速度更精准,地层分层更准确;②获得的模型静校正量精度高,应用于地震资料处理后,同相轴更收敛、连续,剖面成像效果明显改善。结论认为:①双向加权融合建模既具有微测井对地表浅层刻画的精度,又具有层析对近地表中、深层刻画的精度,可以获得准确的静校正量;②用于双向加权融合法建模的微测井资料,尽可能深一些,最好能调查到高速地层,微测井点的密度以能控制表层变化趋势为佳。

In Sichuan Basin with severely undulate terrain and surface conditions, lithology is complex and changeable, and most low-velocity zones are featured by complicated distribution, which lead to low signal-to-noise ratio further bringing about some prominent problems of static correction. The only way to obtain accurate static correction and improve an imaging effect of seismic data is to establish a high-precision near-surface structure. So, a near-surface model was established based on the weighted fusion of small refraction, micro-logging, and first arrival tomography. And in this modeling, weighted fusion is specially conducted vertically and laterally. Results show that(1) the modeling by virtue of two-way weighted fusion method can truly depict the structure of near-surface low-velocity zones and provide more accurate velocity and strata layering;and(2) for the obtained model, its static correction is of high precision. After its application to seismic-data processing, the event is more convergent and continuous, and a section imaging effect is improved obviously. It’s concluded that the modeling based on two-way weighted fusion can ensure the accuracy to describe not only shallow layer by micro-logging but also near-surface middle to deeper layers by tomography, and it can provide accurate static correction. It’s recommended to deepen micro-logging data used for the modeling as much as possible, or it will be better to explore those high-velocity zones. And the density of micro-logging points shall be deployed to control the change trend of surface layers if possible.