层间多次波辨识与压制技术的突破及意义——以四川盆地GS1井区震旦系灯影组为例

Breakthrough and significance of technology on internal multiple recognition and suppression:A case study of Ordovician Dengying Formation in Central Sichuan Basin, SW China

针对四川盆地GS1井区震旦系灯影组及下寒武统筇竹寺组的地震合成记录与实际记录严重不匹配现象,开展层间多次波辨识与压制技术研究。(1)研发了基于反射率法的多次波正演模拟方法,通过叠后和叠前多次波正演模拟等8种手段,结合VSP资料论证了该区井震不匹配主要是由层间多次波造成的。(2)利用剥层法井点和联井剖面多次波正演模拟结果,结合多次波周期性分析,明确了上覆4组速度反转层是灯影组层间多次波的主要来源。(3)在层间多次波准确识别和来源分析的基础上,通过传统Radon方法创新应用,结合基于模式识别的压制技术,突破了由于层间多次波与一次波速度差异小使得现有方法难以奏效的困境,结合基于模式识别的压制技术,形成了适用、有效、可复制的压制处理方案。(4)提出了一种多次波发育强度评价指标,编制了高石梯—磨溪地区灯四段多次波发育强度分布图。该方案提高了井震匹配程度,压制后剖面结构特征更加符合沉积规律,横向分辨率更高,小断裂与小异常体特征更清晰,并在灯影组发现了串珠反射。基于地震波形分类的储集层预测符合率从60%提高到90%,基于双相介质的烃类检测符合率从70%提高到100%。

Aimed at the serious mismatch between the synthetic record and the real data of the Sinian Dengying Formation and the Lower Cambrian Qiongzhusi Formation in the GS1 well area,Sichuan Basin,four aspects of internal multiples identification and suppression were studied.Firstly,a forward modeling method of internal multiple based on reflectivity method was developed.Through eight means such as post-stack and pre-stack forward modeling of internal multiple,and combined with VSP data,it was demonstrated that well-seismic mismatching in this area is mainly caused by the internal multiples.Secondly,the simulation results of interbed multiple forward modeling using the stripping method combined with the internal multiple periodicity analysis showed that four groups of overburden layers with velocity inversion were the main sources of the internal multiples.Thirdly,by identifying internal multiples accurately and using suppression technology based on pattern recognition,an effective and replicable suppression scheme suitable for these formations was established,overcoming the difficulty of the small difference between internal multiple and primary reflection wave which makes the current methods ineffective.Fourthly,an evaluation index of internal multiple intensity was proposed,and the internal multiple intensity distribution diagram of the fourth member of Dengying Formation in Gaoshiti-Moxi area was compiled.This scheme greatly improved the well-seismic match,and the strata sedimentary features are clearer on the new seismic profiles with higher lateral resolution,with which smaller faults and geological anomalies can be identified and a series of the bead reflections in the Dengying Formation are first discovered.The coincidence rate of reservoir prediction based on seismic waveform classification was increased from 60%to 90%,and that of hydrocarbon detection based on dual phase medium theory was increased from 70%to 100%.