论文部分内容阅读
迭代剖面偏移、聚焦分析、叠加能量分析等这些最常用的偏移速度分析算法都是以特定的地下假设条件为依据的,在横向速度变化的情况下这些假设会导致这些算法的失败。一般地说,或者假定地下速度为常速或最多假定速度是随深度变化的。最近的一些改进,包括使用旅行时反演原理来反演求取偏移后同相轴所表现出的曲率与炮检距的函数关系的偏移测量值。旅行时反演无需对地下地质情况做任何假设,但却是一个相当不稳定的方法。因此,一个重要的问题是:“在什么样的条件下,传统的方法会失败,而必须使用旅行时反演法?” 将常用的偏移分析与层析成象结合在一组方程中,虽然根据偏移值算出修正量有用,但对于回答上面的问题来讲是太复杂了。然而,如果限定地下为低起伏的构造,并且假定波以小角度传播,那么这些校正的方程式就可以用等同于传统的校正方程式的形式来近似,不同的只是差一个系数,这个系数取决于可能的横向速度变化的大小、位置和空间波长。这些简单的方程式表明,甚至较长波长的异常也能使校正指向错误方向、使迭代过程发散、并在一定条件下使这些校正的精度大大降低。
The most commonly used migration velocity analysis algorithms, such as iterative section offsets, focus analysis and overlay energy analysis, are based on specific subsurface assumptions that lead to the failure of these algorithms in the case of lateral velocity variations. In general, either the subsurface velocity is assumed to be constant or at most the velocity is assumed to vary with depth. Some recent improvements include the inversion of traveltime inversion to derive offset measurements that determine the offset of the curvature as a function of offset as a function of offset. Traveling backflushing does not require any assumptions about subsurface geological conditions, but it is a rather unstable method. Therefore, an important question is: “Under what conditions can the traditional method fail and the travel-time inversion method must be used?” Combining the commonly used migration analysis and tomography in a set of equations , Although it is useful to calculate the amount of correction based on the offset value, it is too complicated to answer the above question. If, however, the subsurface is defined as a low-lying configuration and the wave is assumed to propagate at a small angle, then these corrected equations can be approximated in the same way as the traditional calibration equations except that they differ by a factor that depends on the likelihood The lateral velocity varies in size, position and spatial wavelength. These simple equations show that even longer wavelength anomalies can point the correction in the wrong direction, diverging the iterative process and greatly reducing the accuracy of these corrections under certain conditions.