The role of polygonal faults in fluid migration and gas hydrate reservoir forming in Southeast Hainan Basin
【摘要】 多边形断层是由未固结沉积物脱水使得体积收缩而在平面上呈现多边形形状,且具有微小断距、分布密集的张性断层。在琼东南盆地深水区的中新世—上新世地层中,利用三维地震相干切片可以发现小规模流体运移通道——多边形断层。同样在二维高分辨率地震剖面上也能发现多边形断层、底辟和同相轴下拉的管状构造,距海底双程走时250ms和300ms位置存在强的似海底反射层(Bottom Simulating Reflector,简称BSR)。利用约束稀疏脉冲反演和地震属性分析表明,多边形断层上部地层的管状构造和模糊反射区为低声波阻抗异常和低频率异常,BSR上为高声波阻抗和高频率异常。多边形断层、管状和底辟构造破坏了琼东南盆地裂后热沉降阶段巨厚的泥岩地层的封闭性,使大量流体垂直和近似垂直向上运移,为天然气水合物形成提供了充足气源。
【Abstract】 The dehydration of unconsolidated sediments made the sediments shrink,then the polygonal faults were formed,they were the densely distributed tensional faults with small fault throws.In the Miocene to Pliocene strata in the deep water zone of Southeast Hainan Basin,the small-scale fluid migration channels which actually were the polygonal faults were found on the 2-D high resolution seismic coherence slices.Meanwhile the polygonal faults,diapir and event pulldown tubular structures were found on the 2-D high resolution seismic sections,and the strong BSR (Bottom Simulating Reflector) exist 250ms to 300ms below the sea floor.The CSSI (Constrained Sparse Spike Inversion) and seismic attribute analysis show that tubular structures and fuzzy reflection zone in the strata above the polygonal faults have low impedance anomaly and low frequency anomaly,while the BSR shows high impedance anomaly and high frequency anomaly.The polygonal faults,diapir and event pulldown tubular structures broke the closure of the extremely thick mudstone strata during the post-fault thermal subsidence period in Southeast Hainan Basin,the structures made a large amount of fluid migrate upwards vertically or nearly vertically,providing sufficient gas source for the gas hydrate formation.
【Key words】 polygonal fault； gas source； gas hydrate； Southeast Hainan Basin；
- 【文献出处】 石油地球物理勘探 ,Oil Geophysical Prospecting , 编辑部邮箱 ,2010年01期