湘西北地区新元古界陡山沱组页岩气成藏条件

摘要

湘西北地区广泛发育新元古界震旦系陡山沱组暗色泥页岩,已有钻井中气显示活跃,揭示出该地区较好的页岩气勘探潜力.在观察野外地质露头的基础上,通过地球化学分析、扫描电镜、X射线衍射、低温氮气吸附、等温吸附等分析测试,对陡山沱组泥页岩的发育及分布规律、有机地球化学特征、储层特征及吸附性能等页岩气成藏条件进行了综合研究,并优选了有利区带.结果表明:湘西北地区陡山沱组暗色泥页岩分布变化大,仅在大庸向斜地区沉积厚度较大,为20～50 rn,有机碳质量分数为0.5％～3.0％,有机质类型以Ⅰ型为主,有机质成熟度为3.0％～4.0％,达到过成熟演化阶段,具备较为有利的生气条件;泥页岩储层矿物成分以脆性矿物为主,质量分数为21％～78.7％,发育多种类型孔隙空间,比表面积和孔体积均较高,多个泥页岩样品等温吸附实验统计显示,甲烷最大吸附质量体积为0.80～1.77 m3/t,泥页岩储层具有较好的储集条件及吸附性能.湘西北大庸向斜地区构造条件相对稳定,保存条件较好,具有有利的页岩气成藏条件,可作为陡山沱组页岩气勘探的有利区带.%Shale of the Neoproterozoic Doushantuo Formation is widely developed in Northwestern Hunan province.With better gas show in shale gas wells,it revealed better gas potential of the Doushantuo Formation shale.Based on outcrop observation,combined with analysis of organic geochemical test,SEM,X-ray diffraction,low-temperature nitrogen adsorption-desorption and isothermal adsorption,the accumulation conditions and characteristics of shale gas of the Neoproterozoic Doushantuo Formation were studied.The results show that the shale development in the study area is not uniform,and the relatively large cumulative depositional thickness is 20-50m in Dayong syncline.The TOC mass fraction of shale is 0.5％-3.0％,the organic matter is mainly type Ⅰ,and the Ro is 3％-4％,which has reached over-mature evolution stage,with favorable conditions for gas generation.The reservoir minerals of shale are mainly of brittle minerals,with mass fraction of 21.0％-78.7％.The various types of pore spaces developed in shale support high specific surface area and pore volume.The maximum methane absorbance is 0.80-1.77 m3/t.All of the characteristics of shale mean the advantageous geological conditions of shale gas enrichment and accumulation.With steady tectonic setting,favorable preservation conditions and advantageous shale gas accumulation conditions,Dayong syncline is favorable for shale gas exploration.