【摘要】 推导了基于角度域共成像点道集的叠前深度层析速度建模公式,提出了一种叠前多级优化联合偏移速度建模方法.通过基于共散射点(CSP)道集的叠前时间偏移速度分析获取初始速度,利用基于角度域共成像点道集(ADCIGs)的叠前深度层析速度反演进行速度更新建模.实现步骤可以概括为:首先,将叠前地震数据映射为CSP道集,利用CSP道集的叠加速度谱进行速度分析得到均方根速度场;其次,通过Dix公式将均方根速度场转换为层速度场,以此进行层析初始速度建模,基于ADCIGs实现叠前深度层析速度反演,最终得到高精度的叠前偏移速度场.断层模型和实际资料试算结果验证了该方法的正确性和有效性.更多还原

【Abstract】 This paper derived the formula of pre-stack depth migration tomographic velocity analysis based on angle domain common imaging gathers(ADCIGs) and proposed a pre-stack joint migration velocity modeling method with multi-stage optimization which gets the initial velocity through the pre-stack time migration velocity analysis on the basis of common scattering point(CSP) gathers and obtains the velocity update through the pre-stack depth migration velocity analysis on the basis of ADCIGs.The implement steps can be summarized as follows: First,make the pre-stack seismic data mapped to CSP gathers and get the root-mean-square velocity by stack velocity spectrum of CSP gathers;then transform the root-mean-square velocity to interval velocity in order to model the initial tomography velocity field;finally obtain the pre-stack migration velocity field with high-precision by pre-stack depth migration tomographic velocity inversion based on ADCIGs.The pre-stack time migration velocity analysis based on CSP gathers can solve dispersion problem of reflection points for inclined layers,get focused velocity spectrum and obtain good initial velocity quickly.ADCIGs are obtained from prestack depth migration,not affected by multi-path problem and free of artifacts,and coupling relation of velocity and depth can be revealed clearly in ADCIGs.The pre-stack depth tomographic velocity modeling based on ADCIGs can be easily implemented without considering complex reflection problems in ray tracing,and each step is updated on the basis of prestack depth migration in the prior step.Through the flatness degree of ADCIGs,it is easy to judge the velocity update and finally achieve a high precision velocity field.Examples of fault model and field dataset shows this method is feasible and valid,but its precision is restrained by the resolution of ADCIGs,and prestack data with low S/N may make impact on inversion results.So before the implement of pre-stack joint migration velocity modelling,data pre-processing need to be carried out for precision of velocity modelling.更多还原