巨厚黄土塬近地表正演模拟及约束层析反演

Forward modeling and constrained tomographic inversion of near-surface in huge loess plateau

塔里木盆地西南部昆仑山前地表主要被黄土层覆盖,低降速层厚度大,纵横向速度变化快,常规的表层建模方法难以精准反映近地表的结构和速度特征,制约地震资料成像精度。通过正演模拟黄土塬近地表结构,利用正演单炮初至层析反演近地表结构,与设计模型进行量化对比,统计反演速度误差,进而用正演模型参数约束层析反演,降低层析反演速度误差。实际地震资料采用微测井、黄土曲线等先验信息约束初至网格层析反演,解决了近偏移距缺失和近炮点初至拾取不准等因素导致的极浅层速度反演误差较大问题,建立了更接近真实地层结构速度趋势的近地表模型,为巨厚黄土塬区地震成像提供了更精确的近地表信息。

The surface of the Kunlun mountain in the southwest Tarim basin is mainly covered by loess.The thickness of the low-deceleration layer is large,and the vertical and horizontal velocity changes rapidly.Conventional surface modeling methods cannot accurately reflect the structure and velocity characteristics of the near-surface,which restricts the imaging accuracy of seismic data.The near-surface structure of the loess plateau is simulated through forward modeling.The first-arrival tomographic inversion of the near-surface structure using forward single shots is used for quantitative comparison with the design model,and the inversion velocity error is counted.Then the forward modeling parameters are used to constrain the tomographic inversion to reduce tomographic inversion speed error.Actual seismic data uses prior information such as micro-logging and loess curve to constrain the first-arrival grid tomographic inversion.The very shallow velocity is soleved for the inversion error caused by factors such as missing short offset and inaccurate picking of the first-arrival near shot point.A near-surface model that is closer to the velocity trend of the real stratigraphic structure,is established to provide more accurate near-surface information for seismic imaging of the huge loess plateau area.