湖南省安化地区寒武系小烟溪组页岩气成藏条件分析

Shale Gas Accumulation Conditions Analysis of Cambrian Xiaoyanxi Formation in Anhua Area of Hunan Province

为查明湖南省安化地区寒武系小烟溪组(∈1x)页岩气勘探潜力,在对页岩气钻井资料分析基础上,结合野外地质调查、大地电磁测量及样品测试结果,研究了该组页岩分布特征、有机地化指标、岩矿组分、储集空间、含气性及保存条件。结果表明:安化地区寒武系小烟溪组暗色泥页岩的厚度普遍都在100 m以上;页岩有机碳含量高、有机质为I型、热演化程度高;页岩中的脆性矿物含量较高,均为硅质页岩岩相类型,具有溶蚀孔、粒间孔、铸模孔和微裂缝四种微观孔隙类型;钻井页岩岩芯现场解吸气含量较低,但实验条件下吸附气含量明显较高,表明发生过页岩气逸散;区内构造以开阔型褶皱为主,断裂相对不发育,页岩层顶板的封闭性较好,但底板的硅质岩中高角度裂缝较发育,易成为页岩气逸散通道。综合分析认为,研究区寒武系小烟溪组具有较好的页岩气成藏物质条件,但钻井所在位置目的层埋深较浅,底板封堵性较差,不利于页岩气保存;往南靠近向斜核部区域页岩气保存条件会更好,具备一定的勘探潜力。

In order to find out the shale gas exploration potential of Cambrian Xiaoyanxi Formation in the Anhua area,Hunan Province,based on the analysis of published shale gas drilling data,combined with field geological survey,magnetotelluric survey and analysis data,research on the shale development characteristics,organic geochemical index,rock and mineral composition,reservoir space,gas-bearing property and preservation conditions of Cambrian Xiaoyanxi Formation have been carried out in this study.The results show that the dark shale of Cambrian Xiaoyanxi Formation in the Anhua area is generally more than 100 m in thickness,developed with high organic carbon content,Type I organic matter and a high degree of thermal evolution;The content of brittle minerals in shale is high,and the lithofacies types are siliceous shale,including four micro pore types:dissolution pore,intergranular pore,mold pore and microfracture;The desorption gas content of drilling shale core was low,but the content of adsorbed gas was significantly higher under experimental conditions,indicating that the shale gas had escaped;The structures in the area are mainly open folds,and the faults are relatively undeveloped.The sealing ability of the shale roof is acceptable,but the siliceous rock in the floor develops high-angle fractures,which would easily become the escape channel for shale gas.The comprehensive analysis shows that the Cambrian Xiaoyanxi Formation in the Anhua area of Hunan Province has ideal material conditions for shale gas accumulation.However,the buried depth of the target layer at the drilling location is shallow and the floor sealing ability is inadequate,which is not preferable for the preservation of shale gas.The area close to the syncline core to the south provides better preservation conditions for shale gas and therefore should lead to certain exploration potential.