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把地面地震资料转换成地下图像可以分两步:聚焦和定位。聚焦要确保不同炮检距的数据对同 同相轴具有积极的作用;定位涉及的是利用给定速度模型将聚焦后的同相轴转换成深度图像 叠前深度偏移可以同时完成这两步,然而对3D资料来说费用是惊人的。叠前时间偏移更经济此,甚至在速度适度变化时对地震波也能很好地聚焦,但存在定位误差的问题。混合偏移是一种划算的深度成像技术,它用叠前时间偏移进行聚焦,用反偏移消除定位误差,然后进行叠前深度偏移正确定位。当横向速度变化不大时,混合技术能产生一个与速度场很吻合的深度图像。当构造十分复杂需要进行叠前深度偏移时,混合偏移的结果可用来产生 个初始速度模型,从而减少建立速度模型时的迭代次数。
Converting surface seismic data into an underground image can be done in two steps: focusing and positioning. The focus is on ensuring that the data for different offsets have a positive effect on the same phase axis; positioning involves converting the focused in-phase axis into a depth image using a given velocity model. The pre-stack depth offset can do both, however, The cost of 3D data is amazing. Prestack time migration is more economical, and the seismic wave can be well focused even when the speed is moderately changed, but there is a problem of positioning error. Hybrid Offset is a cost-effective depth imaging technique that focuses on prestack time migration, removes the positioning error by reverse migration, and then prestacks the depth migration to properly position it. When the lateral velocity changes little, the hybrid technique produces a depth image that closely matches the velocity field. When the structure is complex and requires prestack depth migration, the result of the mixed offset can be used to generate an initial velocity model, reducing the number of iterations when building the velocity model.