Controlling factors of ghosts and the effects on single-channel seismic exploration
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摘要:
鬼波影响地震勘探效果，其中较为典型的是震源鬼波。震源鬼波的变化主要由其相对一次有效反射地震波的延时决定。从鬼波的形成机理出发，借助二维海平面及水平海底模型建立海底反射震源鬼波延时、震源沉放深度、作业水深与炮检距间的数学公式，将确定的震源沉放深度和作业水深带入公式并实现可视化，分析炮检距及震源沉放深度对震源鬼波的影响。结合作业中震源沉放深度的变化状态，分析震源鬼波的间接控制因素的影响，并通过实测数据进行验证。研究表明：小炮检距作业有利于降低鬼波对地震勘探效果的破坏作用，但是炮检距对深部数据影响较小，在平面上大致限于作业水深小于炮检距的海域，在纵向上的影响深度约为炮检距与作业水深的差值；震源鬼波受震源沉放深度的影响要大大超过炮检距的影响，当作业水深＜15 m时，震源鬼波延时变动范围对震源沉放深度变化响应约为对同尺度炮检距变化响应的5倍；海水面的起伏是导致震源鬼波变化的重要因素，选择较好的海况条件作业有利于提高海底及地层反射同相轴波形的一致性及地震波能量的均衡性。
Abstract:Source ghost and other ghosts affect the quality of marine seismic exploration. The variation of source ghost is mainly controlled by its time-delay relative to the primary. Based on the theories of ghosts and the two-dimensional model supposing sea surface and seabed are horizontal, the formulas including source ghost time-delay, source depth, and source-receiver distance were established. The relationship between source-receiver distance and source depth was visualized and analyzed when real values are taken into the formulas, through which the effects on source ghost could be determined using the source-receiver distance and source depth. After that, the indirect controlling factors of source ghost were studied when the changes of source depth during exploration were taken into account, and the results were verified by factual seismic profiles. Research shows that the shorter source-receiver distance, the more conducive to reducing the damage of ghosts to seismic exploration results. The source-receiver distance has a small impact on deep exploration results, only on the data acquired in where water depth is less than the source-receiver distance, and the affected length of the data is between seabed and the length of the source-receiver distance below seabed. The effect of the source-depth to the source ghost is much greater than that of the source-receiver distance. When water depth is less than 15 m, the response of the variation range of ghost time-delay to the variation of focal depth is about 5 times that of the response to the variation of offset on the same scale. The fluctuation of the sea surface is an important factor leading to the change of the ghosts. The exploration under good sea conditions is conducive to improving the resolution of single channel seismic data and the consistency of its reflection event.
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Key words:
- single-channel seismic /
- ghosts /
- source-receiver distance /
- source depth
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