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使用偏移垂直地震剖面(VSp)的旅行时间,应用迭代最小平方反演方法可以估算地下的二维倾角。利用合成数据进行试验表明,用直达波或一次反射的旅行时间,由这种反演技术能够估算一个钻井附近的倾角。这种反演方法实质上是一种“剥层”方法,即先估算浅层的倾角,然后估算深部的倾角。几个实例表明,当震源偏移距与层深度的比率很小时,一次反射是主要的波。旅行时间反演还需要精心算层速度和正确的校正静。如果不考虑这些困难和普遍存在的非单值性问题,旅行时间反演可以产生一个正确的地层模型,以用于实际数据的检验。
Using the travel time of the offset vertical seismic profile (VSp), we can estimate the two-dimensional subsurface dip by applying the iterative least squares inversion method. Experiments using synthetic data show that this inversion technique can estimate dip near a well using direct travel or once-reflected travel time. This method of inversion is essentially a “delamination” method, which estimates the dip of a shallow layer and then estimates the depth of dip. Several examples show that primary reflection is the dominant wave when the ratio of source offset to layer depth is small. Travel time inversion also requires elaborate layering and correct calibration. Without accounting for these difficulties and ubiquitous non-singularity problems, travel-time inversions can produce a correct formation model that can be used to test actual data.