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常规叠后地震速度分析通常基于三个假设条件,即横向速度均匀、小炮检距、水平反射层。这类假设不符合我国地质构造的特点。为此,本文提出叠前时间偏移解析速度分析方法。该法通过研究共成像点道集上同相轴的深度随炮检距的变化规律,得出以下结论1同相轴的深距曲线为抛物线;2同相轴的深度误差与速度的相对误差成正比;3同相轴的深度误差与真深度成反比;4同相轴平直时,成像深度为真深度。其主要实现步骤为首先利用三次叠前时间偏移道集上同相轴的时差,解析求取这种时差(或称延迟)为零时所对应的速度,此速度即为所需的成像速度;然后利用此速度进行叠前时间偏移处理,通过对实际资料处理结果的观察可以看出,该法简便实用、效果明显。
Conventional poststack seismic velocity analysis is usually based on three assumptions, namely, a uniform transverse velocity, a small offset, and a horizontal reflection layer. Such assumptions do not accord with the characteristics of China’s geological structure. To this end, this paper presents a prestack time migration analysis speed analysis method. By studying the variation law of the depth of co-occurrence axis of co-imaging point gathers with offset distance, the following conclusions are drawn: 1 The deep-range curve of the events is a parabola; 2 The depth error of the events is proportional to the relative error of velocity; 3 The depth error of the in-phase axis is inversely proportional to the true depth. 4 When the events are straight, the imaging depth is the true depth. The main steps are as follows: Firstly, using the time difference of the three sets of prestack time migration gathers, the velocity corresponding to the time lag (or delay) is obtained by parsing, which is the required imaging speed; Then using this speed for prestack time migration processing, through the actual data processing results can be seen, the method is simple and practical, the effect is obvious.