速度模型反演的CFP方法

针对叠前深度偏移速度模型的建立，本文深入研究了应用CFP技术进行速度模型反演的两种方法(即同步反演和异步反演)。同步反演是指同时反演聚焦算子和速度模型，通过调整速度模型来调整DTS响应，使道集拉平并且位于零线，每一次调整速度模型之后都要计算聚焦算子、CFP道集和DTS响应，并根据DTS响应计算速度模型的修正量。这种方法基于等时原理，速度模型的调整和DTS道集的拾取紧密联系在一起，该方法直观可靠，主要工作量在于DTS响应的拾取。算子和速度模型的异步反演则是先根据误差对称准则迭代计算正确的聚焦算子，然后根据算子反演速度模型，两个步骤截然分开，速度模型的反演不再涉及DTS响应的拾取，该方法间接求取速度模型，大大减少了拾取的工作量。和常规的偏移速度分析方法相比，CFP方法可以在反射界面的单个几何点上进行，不需要区域性重复偏移，大大减少了计算量；它也不需要常规方法中的小炮检距假设或小倾角假设，适宜复杂地下介质的偏移速度分析。文中合成记录的速度反演取得了满意的结果，并对实际资料的反演进行了初步实验。

CFP method for velocity model inversion

In face of the problem of building prestack depth migration velocity model, the paper deeply studied two methods for inversion of operator and velocity model in CFP half migration domain,that is synchronous inversion and asynchronous inversion.The former adjusts DTS response to align gather's event and to position zero timing line by changing velocity model.Each change of velocity model is followed by calculating focusing operator,CFP gather and DTS response and then using DTS response to calculate corrections of velocity model.The method mainly uses isochronal principle,in which the modification of velocity model and the picking up DTS gather are closely related together.The method is straightforward and reliable.The main efforts are in picking up DTS response.The asynchronous inversion of operator and velocity model is iterative calculation of correct focusing operator first according to the principle of error symmetry,then inversion of velocity model is proceeded on the basis of operator separately,that bears no relation to picking up DTS response.The method got velocity model indirectly but greatly reduced the work effort of picking up. In comparison with velocity analyzing method in an ordinary migration domain,the analysis in CFP half migration domain can be carried out at single geometric point on reflection interface and no windowed re migration is needed,which greatly reduced computational effort;furthermore,there is no assumption of short offset or small dip that often exists in ordinary migration methods,that is suitable for analysis of migration velocity in complicated subsurface medium.The test results with synthetic and real data show that the method is feasible.