地震沉积学中90°相位转换技术适用性的讨论

A discussion on applicability of 90°phase shift in seismic sedimentology

地震沉积学理论及应用技术研究中90°相位转换技术是地震沉积学研究的核心技术之一,但在实际研究与应用中,该技术并未取得如期的成果。在地震勘探原理中,地震反射同相轴代表着具有波阻抗差的地层界面。90°相位转换拟通过相移的方式,将代表着地层界面的地震反射同相轴赋于岩性地层的意义。由于地下地层的复杂多变,多种岩性频繁薄互层。利用薄互层地质模型的地震正演模拟结果,证实地震反射同相轴并不能与地层界面一一对应,因此,地震剖面中的同相轴是多套薄互层组合效应。受地震资料分辨力的限制,90°相位转换后的地震资料既不能将原始地震资料由界面型地震剖面转换成岩性地层剖面,也缺乏明确的地质含义,其在地震构造解释和地震岩性解释中的应用能力均很有限,所以很难称其为地震沉积学的应用技术。因此,将90°相位转换技术作为地震沉积学的核心技术并不合适,该技术无法提高地震资料分辨能力,也不能精确地将地震剖面转化成岩性剖面。

The approach of 90°phase shift has been espoused as one of the core techniques in seismic-based sedimentology since 1998,when systematic researches were launched on the theories and application techniques of seismic-based sedimentology.However,its practical implementation is unsatisfactory.According to the philosophy of seismic prospecting,seismic events represent stratigraphic interfaces with impedance contrasts.The practice of 90°phase shift is intended to transform interfacial events into rock formations.Subsurface complexities often show as frequently interbedded thin layers,the interfaces of which could not be one-to-one correlated with seismic reflections as per forward modeling.This means that a reflection is the combination of seismic responses from a certain number of thin layers.Due to the limitation of seismic resolution,the operation of 90°phase shift cannot convert seismic data from interfacial events into lithologic sections;besides,such an operation is geologically meaningless and cannot yield good results for structure and lithology interpretation.Consequently,it may not be treated as a key technique in the study of seismic-based sedimentology,as it neither improves resolving power of seismic data nor yields lithologic sections from seismic sections.