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在现代的石油勘探中,具有较简单构造形态的勘探目的层,往往被非常复杂的构造体如盐丘或其它类型的底辟、滑动层位(Olistostromes)、或掩冲区的前沿带等构造体所覆盖。在这些情况下,作常规的反射地震勘探时,由于下去和上来的射线彼此颇为靠近,不是在复杂体下面得不到反射,就是由于复盖体的非均质性,实际不可能作可靠的偏移校正深度显示而大多数都失败了。“下射”(Undershooting)技术利用了不穿过复杂体的地震射线路径来躲开这些困难,例如在盐丘的一边放炮而在另一边记录。由于在此方法中采用了大的炮检距,关于共深点迭加及偏移校正深度显示的时差校正的特殊考虑及计算过程都得到了发展。在许多情况下,复杂干扰体的位置是预先知道的。放炮和记录程序因而能针对此已知情况而保持在最小范围。如果不知道复杂体的位置,那么就必须用许多种炮检距进行较大范围的地震工作。在本例中,复杂体的大概位置是可以从观测中推测出来的。为了反映这一新的地震方法的效果,本文还提供了某些成果资料。
In modern petroleum exploration, exploration target formations with simple structures are often constructed by very complex structures such as salt domes or other types of diapirs, Olistostromes, or foreland zones of the lithosphere Body covered. Under these circumstances, it is practically impossible to be reliable due to the inhomogeneity of the covering body in the case of the conventional reflection seismic survey, since the rays going up and going up close to each other are either not reflected below the complex body Most of the offset correction depths have failed. Undershooting techniques utilize seismic ray paths that do not pass through complex bodies to escape these difficulties, such as shooting on one side of the salt dome and recording on the other. Due to the large offsets used in this method, special considerations and computational processes have been developed for the time difference correction of co-depth stacking and offset correction depth display. In many cases, the location of complex interferers is known in advance. The shooting and recording procedure can thus be kept to a minimum for this known situation. If you do not know the location of the complex body, then a large range of seismic work must be done with a large variety of offset distances. In this case, the approximate location of the complex can be inferred from the observations. In order to reflect the effect of this new seismic method, this article also provides some results.