南川地区地表灰岩大面积出露,地震资料信噪比较低,且地下构造复杂、地层倾角较陡,属于典型的地表地下双复杂地震地质条件。单一的速度建模方法无法获取准确的速度模型,进而影响地震成像精度,难以有效指导该区水平井钻探工作。针对这一问题,通过分析层位层析和网格层析两种速度建模方法的优缺点,结合南川地区的实际资料特征,在构造约束的基础上进行逐层网格层析速度反演,即通过拾取纵向速度变化比较明显的地震标志层,由浅至深逐层约束网格层析反演,较好地解决了该区地表地下双复杂地震地质条件对速度反演的影响,为叠前深度偏移提供了较高精度的深度域速度模型。通过实际应用,对南川工区地震资料的成像精度改善明显,基本满足了该区页岩气勘探对地震资料的需求。

All the reasons that the surface limestone is exposed in a large area, the signal-to-noise ratio of seismic data is low, the underground structure is complex, and the dip angle of strata is steep make Nanchuan area to be a typical double-complex seismic geological condition of surface and underground. As the single velocity modeling method cannot obtain the accurate velocity models, it in turn affects the seismic imaging accuracy and is difficult to effectively guide horizontal well drilling in this area. In order to solve this problem, the velocity inversion of layer by layer grid tomography is carried out on the basis of structural constraints by analyzing the advantages and disadvantages of two kinds of velocity modeling methods, such as horizon chromatography and grid tomography, and combined with the actual data characteristics of Nanchuan area. That is, by picking up the seismic landmark layer with obvious longitudinal velocity variation and layer-by-layer constrained grid tomographic inversion from shallow to deep, the effect of surface and subsurface complex seismic geological conditions on velocity inversion is better reduced, and a higher precision depth domain velocity model is provided for the front depth offset . Through practical application, the imaging accuracy of seismic data in Nanchuan work area is improved obviously and basically meets the demand of shale gas exploration in this area.