海底天然气水合物层界面反射AVO数值模拟  

AVO numerical simulation of gas hydrates reflectors beneath seafloor

作　　者：阮爱国 李家彪[1] 初凤友[1] 李湘云[1] 

机构地区：[1]国家海洋局第二海洋研究所国家海洋局海底科学重点实验室,杭州310012

出　　处：《地球物理学报》2006年第6期1826-1835,共10页Chinese Journal of Geophysics

基　　金：国家边缘海"973"项目(G2000046704)资助

摘　　要：本文采用AVO数值模拟方法,共选取水合物系统分层结构6个模型,对水合物、游离气和饱水沉积物接触界面的反射特征进行了数值模拟,研究了BSR及双BSR的存在条件与水合物体系垂向分布的关系,对一些现象从理论上进行了阐明.主要结论是:(1)强的似海底反射界面BSR与游离气体的存在密不可分,实际地震剖面中的“BSR”可能不对应水合物而只对应气体,无明显BSR的地方可能有水合物.(2)水合物顶部有可能存在游离气体,它可以在正常BSR(BSR1)之上形成另一个具有正极性的似海底反射界面BSR2.(3)正常BSR之下的双BSR(BSR0)其弹性机理有两种可能,一是水合物之下游离气上升迁移遇到某种阻隔层或不同气体组分的自然分层所造成的气体垂向分布的梯度性差异;二是当水合物之下的游离气体中存在残存的水合物时,同样会形成一定强度的似海底反射,在这种情形下BSR0的极性比较难以判断,取决于残存水合物上下游离气的饱和度和残存水合物的厚度.The AVO numerical method is used to 6 models of layered gas hydrates systems beneath seafloor, composed of methane hydrate bearing sediment, free gas bearing sediment and saturated sediment, to simulate the formation mechanism of BSR, double BSR and the vertical distribution of gas hydrates system and to give theoretical explanation of some practical problems. The main conclusions are as follows： （ 1 ） The presence of evident ocean bottom simulating reflector （BSR） is closely related to the existence of free gas and the seismic profile ＂BSR＂ maybe is not uniquely linked with methane hydrate but only shows the existence of gas. Inversely, methane hydrate may exist at the place without obvious BSR. （2）Free gas is possible to exist on the top of methane hydrate and forms a positive BSR above the normal BSR （BSRI）. （3） There are two possible elastic mechanisms for double BSR0 under normal BSR1. If the methane gas meets some obstruct layer on the path of upward migration or different gas components naturally are stratified, the vertical gradient distribution of methane gas would be formed with upper part saturation higher than lower part resulting in a negative reflector. On the other hand, if some residual hydrate exists in the free gas layer under methane hydrate, some kind of BSR with certain amplitude would occur. But for this case the polarity of BSR0 maybe is difficult to be discriminated, depending on the gas saturation above or beneath the residual hydrate and the thickness of residual hydrate.

关 键 词：天然气水合物 层界面 BSR AVO 数值模拟 

分 类 号：P738[天文地球—海洋地质]