特殊岩性体下伏地层变速构造成图方法及应用

Method of velocity varied structure mapping of underlying strata of special lithologic body and its application

在南海东部地区的油气勘探进程中,常见到局部发育的砂砾岩、灰岩等特殊岩性体,其厚度突变且与围岩存在巨大速度差异,地震偏移速度场往往难以体现其局部速度特征,常导致其下伏地层构造成像产生假象,传统的构造成图方法难以揭示真实构造形态,为勘探、开发井位部署带来较大困扰.为此,提出了一种新的变速构造成图方法.在井、震标定基础上,通过特征地震属性分析及体属性雕刻获得特殊岩性体的空间分布,再采用井、震速度趋势匹配校正方法修正地震速度场的速度趋势,最后基于声波测井数据对特殊岩性体进行速度充填并与地震速度体融合以构建新的速度模型用于变速构造成图.将该方法应用于南海东部番禺地区低幅度构造勘探实践,基本解决了该地区浅层砂砾岩高速异常体导致的速度陷阱问题,揭示了砂砾岩体下伏地层的真实构造形态,与钻井结果吻合,对类似特殊岩性体下伏低幅度构造目标评价具有一定参考意义.

In the process of oil and gas exploration in the eastern South China Sea,locally deposited geological bodies such as glutenite and limestone are common.These locally deposited geological bodies were also called special lithologic body.They usually shows a huge velocity difference with the surrounding rock and changes sharply in thickness,and the seismic migrating velocity field often fails to show their local velocity characteristics,which often leads to structure illusion of their underlying strata.The traditional structural mapping method is difficult to reveal the real structure form,which brings great trouble for well deployment.Therefore,a new velocity varied structure mapping method is proposed.On the basis of well and seismic calibration,the spatial distribution of velocity anomalies is obtained through characteristic seismic attribute analysis and 3D seismic volume attribute carving,and then the trend of seismic velocity field is corrected by well and seismic velocity trend matching correction.Finally,the velocity anomalies is assigned with interval velocity value based on acoustic logging data and then fused with seismic velocity volume to build a new velocity model for velocity varied structure mapping.This method is applied to the tectonic confirming in Panyu Area of eastern South China Sea,drilling results show the method can basically solved the problem of velocity trap caused by overlying sandy conglomerate high-speed anomalies in this area,and reveals the real structural form of the underlying strata.The method and case study might provide reference for the evaluation of low amplitude structural targets under the special lithologic body.