宜昌斜坡区南华系-震旦系断坳结构发现及其地质意义

宜昌斜坡区钻获南方复杂构造区下寒武统水井沱组、下震旦统陡山沱组高含气页岩,首次实现了古老层系页岩气重大发现,南华系-震旦系构造-沉积格局是认识盆地构造属性及古老页岩气富集的关键。基于前人的研究成果,开展了宜昌地区南华系-震旦系沉积岩石特征、地震资料分析。结果表明:宜昌及周缘存在克拉通内Ⅰ型(宜昌型)、克拉通边缘过渡区Ⅱ型(长阳型)断坳结构控制的沉积区类型。在经历了早期断陷、中期成冰、断坳转换及晚期坳陷4个演化阶段,断坳结构控制了陡山沱组及灯影组-水井沱组ⅠⅠ型台地边缘-斜坡和ⅠⅡ型台内洼地及Ⅱ型陆棚相沉积区,富有机质页岩相对发育。结论认为:Ⅰ型、Ⅱ型断坳结构发育区是陡山沱组-水井沱组自生自储页岩气的规模聚集区;Ⅰ型控制下灯影组旁生侧储边缘滩也是天然气聚集的有利场所。

Discovery and geological significance of Nanhua-Sinian fault-depression,Yichang slope

In the slope of Yichang, the drilling of the Lower Cambrian Shuijingtuo Formation and Lower Sinian Doushantuo Formation with high gas shale in the southern complex structural area announces significant discovery of ancient shale gas.The Nanhua-Sinian tectono-sedimentary framework in Yichang slop is key to understanding the basin tectonic attribute and ancient shale gas accumulates.Based on the previous geological research results, characteristics and seismic data of Nanhua-Sinian were observed and analyzed.It is shown that there are two fault-depression types, Inter-cratonic typeⅠof Yichang and cratonic margin transition zone typeⅡof Changyang.After experienced four evolutionary stages, early fault, middle cryogenian, fault-depression transition and late depression, the fault-depression control platform slope facie of type Ⅰ_Ⅰ, platform inner depression facie of type Ⅰ_Ⅱ, and shelf sedimentary facies of type Ⅱ, which belong to Doushantuo and Dengying-Shuijintuo Formations structure sedimentary area, relatively developed organic shale.It is concluded that the zones of type Ⅰ and type Ⅱ, deep fault-depression are shale gas scale areas of source rock-reservoir of Doushantuo and Shuijintuo Formations.In addition, type I is the favorable gathering place of the natural gas reservoir, beside source rock, Dengying Formation platform edge beach.