天然气水合物地震似海底反射现象AVO正演模型研究

似海底反射(BSR)现象是用人工地震方法识别含天然气水合物沉积地层的重要标志之一。针对水合物沉积物的悬浮、颗粒接触和胶结3种微观模式,进行了似海底反射现象正演模型的研究,考查了BSR现象产生的地震地质原因和运用AVO判断游离气的适用性。研究结果表明:在地震合成记录的帮助下,结合AVO变化曲线,可以认为BSR的成因有两种情况。实际工作中需要运用多种信息的综合分析而不是一种简单固定的模式来解释BSR的复杂成因。水合物沉积的3种微观模式都存在水合物的临界饱和度,当介质中水合物饱和度小于临界饱和度时,可以通过AVO曲线的变化形态来判断水合物沉积层下伏介质中是否含有游离气;而大于临界饱和度时,AVO技术则难以适用。AVO曲线形态、BSR现象与游离气三者之间存在复杂的关系,同样需要通过多种信息的综合分析来解释。

STUDY OF MODELING SEISMIC BOTTOM SIMULATING REFLECTOR FOR NATURE GAS HYDRATE

Bottom simulating reflector(BSR) is an important seismic indicator for gas hydrate sediment. With three kinds of macro models of hydrate sediments,this paper models the BSR, and investigates the seismic and geological cause to BSR and the applicability of AVO used to indicate the existence of free gas. The research results demonstrate that there are two kinds of causes to BSR. All available information can be put together to interpret the complicated causes. There is a critical concentration for all three macro models of hydrate sediments.When the hydrate concentration is smaller than the critical concentration, the AVO curve shape can be used to indicate the existence of free gas in lower medium. While bigger than the critical concentration, AVO is hardly applicable. All available information should be combined to analyze and interpret the complicated relationship among AVO curve shape, BSR and free gas.