层析+折射约束迭代反演近地表建模方法及应用探索

Exploration and application of near-surface modeling method by tomography and refraction constrained iterative inversion

塔西南山前带是塔里木盆地重要的勘探接替领域之一,其地表为巨厚黄土覆盖,黄土厚度可达500 m以上,速度在纵、横向上变化快,表层结构复杂。为改善地震成像效果,针对复杂地表区表层模型精度难以满足需求的问题,开展了拟合时深曲线量板、层析反演及折射反演等方面研究工作。结果表明:多种表层建模方法综合运用是提高近地表模型精度的有效途径;黄土曲线量板可反映连续介质区近地表速度变化规律;层析+折射约束迭代反演近地表建模方法能够将模型精度误差控制在5%以内;逐级递进约束层析反演可拓展可信速度场深度约1500 m。以上成果认识,对类似探区构建高精度近地表模型及提高地震成像精度具有指导意义。

The southwest piedmont of the Tarim Basin is one of the important exploration successor fields,whose surface is covered with extremely thick loess,with a thickness of over 500 m.The velocity changes rapidly in both vertical and horizontal directions,and the surface structure is complex.In order to improve the seismic imaging effect and address the issue of difficulty in meeting the accuracy requirements of surface models in complex surface areas,research has been carried out in areas such as fitting time depth curve template,tomography inversion,and refraction inversion.The results indicate that the comprehensive application of multiple surface modeling methods is an effective way to improve the accuracy of near-surface models;the loess curve template can reflect the variation law of near-surface velocity in the continuous medium area;The near-surface modeling method by tomography and refraction constrained iterative inversion can control the model accuracy error within 5%;step-by-step progressive tomography constrained inversion can expand the depth of credible velocity field by about 1500 m.The above achievements have guiding significance for constructing near-surface models of high precision and improving seismic imaging accuracy in similar exploration areas.