低序级断层波动方程正演及特征分析

低序级断层是复杂断块油藏勘探开发的重要研究内容,对油田开发后期落实剩余油分布、解决注采矛盾具有重要意义.本文采用声波方程有限差分正演模拟,对以下几种情形进行了研究:(1)低序级断层与埋深、主频以及信噪比之间的关系;(2)观测系统对断层的影响;(3)物性差异产生的假断层问题;(4)大断层衍生出小断层的正演问题;(5)断层破碎带的影响以及断层封堵带含流体的影响.在上述理论模型正演分析的基础上,根据胜利油田典型构造带的地震剖面建立速度模型,研究了不同组合模式的低序级断层的识别能力,最后分析了波动方程正演模拟和褶积合成地震记录的区别.通过对低序级断层正演模拟特征的分析,得出了不同资料质量、不同地质情况以及不同组合模式下,能够准确识别的断层的极限.理论上能够识别的断层最小断距为7 m左右,最小可能会达到5 m,子波主频适当提高,数据采集时炮点和检波点越密集,道间距越小,多个断层的横向或纵向间隔越大,断层的落差越大时,越能够准确地定位断点并确定断层位置.本文研究成果对油田科研生产中低序级断层的正确判别以及提高断层检测方法的可信度方面具有重要意义.

Wave equation forward modeling and characteristics analysis of low-level sequence faults

Low-level sequence faults are important for the exploration and development of complex fault-block reservoirs and of great significance for implementing the remaining oil distribution and solving the contradiction between injection and production in the later stage of oilfield development.The finite difference forward modeling based on wave equation had been adopted to study the following situations:(1)the relationship between the low-order fault and the main frequency,buried depth,and signal-to-noise ratio of the seismic wave,(2)influence of observation system on low-order faults,(3)false fault problem caused by physical differences,(4)the forward problem of small faults derived from large faults;(5)the influence of fault fracture zone and the fluids in fault blockage zone.Based on the above analysis,different models of low-level faults with different combination modes designed on the basis of the typical tectonic belt of Shengli Oilfield are studied.Finally,the difference between wave equation forward modeling and convolutional synthetic seismic record is analyzed.According to the analysis,we concluded the limits of faults that can be accurately identified under different data quality,different combination modes and different geological conditions.In the general data through high-precision processing,the theoretically identifiable fault minimum break is about 7 m,and the minimum may reach 5 m.If the dominant frequency is higher,the trace interval is smaller,the lateral or longitudinal interval is larger and the fault throw is larger,the low-level faults will be identified more accurately.The results are of great significance for correct identification of low-level faults and the improvement of the reliability of fault detection methods.