不同基准面上的速度场及时深转换

速度场及时深转换基准面的选取与速度分析基准面、静校正基准面密切相关。鉴于目前常用的两步法静校正来讲，速度建场和时深转换时，有2个面可供选择：一是速度谱分析面，即CMP面；一是统一的固定水平基准面，即最终成果剖面的零时间起始面。选取不同的基准面进行速度场研究及时深转换，所得最终构造图精度不同。笔者分别在这2个不同基准面上进行了速度场及时深转换研究，并提出使用在一个排列长度范围内，对检波点高程和炮点高程进行统计平均的方法，作为对应时间域CMP面的深度域时深转换面。对比研究表明，在此面上进行速度场研究和时深转换，在不加任何井资料约束前提下，所得平均速度场比常用的在统一水平基准面求取的平均速度场精度高，时深转换后所得最终构造图的对井误差，小于在统一水平基准面上进行的时深转换结果。

THE VELOCITY FIELD AND TIME-TO-DEPTH CONVERSION ON DIFFERENT DATUM PLANES

In extracting average velocity fields, the choice of different datum planes can lead to different time to depth conversion results. In the two step static correction used at present, there are two datum planes to construct the average velocity field and perform the time to depth conversion: one is the velocity spectrum analyzing datum plane, i.e., the CMP datum plane, and the other is the final seismic datum plane, i.e., the common datum plane. The velocity field and time to depth conversion were studied on these two different datum planes, and a method was put forward for deriving a smoothed near surface plane for time to depth conversion by averaging all elevations of each receiver and each shot point within the scope of a CMP gathered. A case study shows that this method can provide higher precision velocity field and structure map without using any borehole data than the routine velocity field study method on common datum plane.