库车坳陷盐下构造畸变特征分析和校正

Analysis of distortions of subsalt structure and its correction in Kuqa depression

库车坳陷是塔里木油气勘探的主要工区,在库车坳陷盐下构造油气勘探中,因受上覆地层构造形态和层速度结构的影响,盐下构造形态及高点位置在时间域地震剖面上发生畸变,与地下实际构造形态存在差异,甚至形态迥异。为了研究构造畸变的变化规律,根据地震波传播的动力学特征,将盐下构造畸变分为两类,即绕射型和反射型。通过模型正演,分析了影响盐下畸变程度的两个重要因素(盐上构造形态和层速度结构),在此基础上将库车坳陷盐构造划分为4种基本类型,并引入盐下构造水平参考线(Lsh)和平均速度变化趋势线(Vav)的概念,根据上覆地层变化情况与盐构造类型的不同,分析Vav,Lsh的形态和变化趋势,判别盐下构造在时间域剖面的真伪和畸变情况,从而掌握时间域剖面构造畸变规律。在以上研究的基础上,结合叠前深度偏移和时深转换方法,可有效校正盐下构造畸变现象,恢复构造真实形态。

Kuqa depression is a main oil-gas prospect in Tarim Basin.Because of the effect of attitude and interval velocity structure of the overlying formation,the attitude and high of the subsalt structures are distorted on seismic time sections,some of them are quite different from the real subsurface geology.According to the dynamic characteristics of seismic wave,two kinds of subsalt structural distortion can be identified:diffraction-related and refection-related.With forward modeling,the author investigated the 2 key factors:overlying attitude and interval velocity structure,that affect the degree of distortion of subsalt structure.Salt structures were classified into 4 in Kuqa depression.2 concepts were defined.They are horizontal reference line(Lsh)and average velocity trend line(Vav)of the subsalt structure.By studying the shape and trend of Vav and Lsh,the distortions of subsalt structures on seismic time section can be identified.Then by combining prestack depth migration and time-distance conversion,real attitude were restored.