联合结构张量与运动学反偏移的立体层析数据空间提取与反演策略研究Ⅱ:实践

Inversion strategy and data space extraction for stereo-tomography based on a combination of structure tensor and kinematic demigration.Ⅱ:practice

为降低立体层析反演实际应用中绕射波、多次波和侧面波等对提取最佳数据空间(炮点坐标、检波点坐标、炮点P参数、检波点P参数、旅行时)精度的影响,提出了获取更佳立体层析数据空间的两步法策略。首先利用初始速度进行叠前深度偏移,然后在成像域实施运动学反偏移以提取更佳数据空间参数。将二维叠前成像体视为三维数据,采用三维结构张量算法一步即可精确获得运动学反偏移所需的构造倾角和剩余曲率信息。不同于理论数据,对于实际数据采用了在若干不同偏移距数据体的共偏移距成像道集上分别选取有效数据点,然后分别延拓的策略,以保证通过延拓挑选出的数据点更均匀、可靠。最后,利用运动学反偏移将选出的成像域数据点的运动学信息反偏移到数据空间,获得更佳立体层析数据空间。针对南海某二维实际数据,对两步法提取的数据空间进行立体层析反演,建立偏移速度模型,最终的叠前深度偏移结果表明:两步法策略有效地提高了实际数据的反演精度,是一种获得更佳立体层析数据空间的有效途径。

In stereo-tomographic inversion,diffractions,multiples and side waves have adverse impact upon optimal data space extraction(source position,receiver position,source P parameter,receiver P parameter,travel time).This paper proposes a two-step scheme to counter that.First,Prestack depth migration(PSDM)is implemented using initial velocity.Then,kinematic demigration is implemented to extract the data space parameter.We used a 3D structure tensor,with the 2D pre-stack depth-migrated dataset used as a 3D volume,to obtain residual move-out(RMO)and structural dip for kinematic demigration.For field data,a set of key horizons were selected manually in several select depth-migrated common offset gathers,and these were extrapolated along the offset axis based on the RMO chosen in advance to produce reliable and well-distributed initial high-density data points.Finally,kinematic demigration was implemented to inverse the kinematic information of selected data points to obtain a refined data space for stereo-tomography.We applied the strategy to 2D field data from the South China Sea.A migration velocity model was built based on the data space achieved using the proposed scheme and then PSDM was implemented.The migration results demonstrate that the strategy is effective for achieving best data space for stereo-tomographic inversion.