碳酸盐岩缝洞储层地震反射波特征及其与油气的关系

碳酸盐岩复杂的成岩作用和储集空间的演化史,导致了其特有的、以缝洞体为主的储集空间在横向上有着较强的非均质性,使得钻探成功率降低,提高对碳酸盐岩缝洞体反射特征的认识,则可大大降低勘探风险。为此,采用弹性波动方程模拟了不同形态碳酸盐岩溶洞储层模型的地震反射波特征,总结了溶洞在正演偏移剖面上最大波峰振幅与溶洞大小的关系,同时对波形做了相关分析,得到以下结论:①随着溶洞宽度的增加,溶洞对应的振幅是不断增大的;②振幅随溶洞宽度增加是有极限的,当溶洞宽度大于菲涅尔带半径时,其宽度对振幅几乎无影响;③溶洞在剖面上的一般表现特征为"串珠"状或"羊排"状,在宽度和高度固定的情况下,溶洞表面积越大,振幅越大;④最大波峰振幅曲线有助于识别溶洞。塔里木盆地TH油气藏的勘探实践证明了该方法的可靠性,也为类似油气藏的勘探提供了技术支撑。

Reflection characteristics of seismic waves of carbonate cave reservoirs and their significance to the oil and gas discovery

Due to the complex diagenesis of carbonate rocks and the long term evolution of reservoir space, the carbonate cave reservoirs dominated by caves and fractures are of great heterogeneous laterally, which lowers the oil and gas exploration success ratio. Therefore, it is quite necessary to have a better understanding of seismic reflection curve characteristics of carbonate cave reservoirs thus to significantly mitigate the exploration risk. In view of this, elastic wave equations were applied to simulate the seismic reflection waves of different carbonate cave reservoir models. The relationship between the maximum peak amplitude and karst cave size on the forward migration section was also summarized and the related analysis was made of the seismic waveforms. The following findings were made. First, with the enlarging width of caves, the corresponding amplitude is increasing; however, when being larger than the Fresnel zone radius, the cave width has no effect on the amplitude. Second, on the section profile, caves are presented in beaded like or lamp chops shapes; with the fixed width and height of caves, the larger the superficial area of caves, the higher the amplitude. In conclusion, the maximum peak amplitude of seismic curves contributes a lot to the identification of caves. The successful practice in the TH oil and gas field， northern Tarim Basin, validates that this method is reliable and provides a robust technical support for the discovery of those similar hydrocarbon reservoirs.