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.