基于角度域共成像点道集的3D VSP速度分析方法研究

获得高精度的3D VSP偏移速度场是3D VSP资料井周构造高精度成像的关键问题和难点之一。目前,基于角度域共成像点道集(Angle Domain Common Image Gathers,ADCIGs)的速度分析方法已经成为地面三维地震资料叠前深度偏移中速度模型建立的有效工具。借鉴地面地震资料基于ADCIGs的速度分析方法,开展了基于ADCIGs的3D VSP资料叠前深度偏移速度分析方法研究。首先给定一个初始速度场进行偏移,形成ADCIGs;接着通过剩余曲率计算获得估计速度与真实速度之比的速度谱函数;最后根据速度谱进行速度迭代更新和3D VSP资料偏移成像。模型数据和实际资料试算结果表明,该方法可以较好地改善3D VSP资料成像精度,提高3D VSP资料描述井周细微构造的能力。

To obtain high-precision velocity model is a key step for high-precision borehole surroundings structural imaging by 3D VSP data. Velocity analysis based on angle domain common image gathers(ADCIGs) becomes an available tool to build a good velocity model for pre-stack depth migration(PSDM). Taking the experience on surface seismic data for reference,the velocity analysis technique based on ADCIGS is introduced in velocity model building for pre-stack depth migration of 3D VSP data. Firstly,ADCIGs are formed by migration from the given initial velocity field. Secondly,the velocity spectral function,that is the ratio of estimated velocity to true velocity,can be calculated by residual curvatures of ADCIGs. Finally,the velocity can be iteratively updated and 3D VSP data migration can be carried out with velocity spectrum. The results of model and real data test show that this method can greatly improve the accuracy of 3D VSP data imaging and enhance the capacity for characterizing the micro structures of borehole surroundings with 3D VSP data.