川东北沙溪庙组天然气地球化学特征及地质意义——以五宝场地区为例

Geochemical characteristics and geological significance of Shaximiao Formation in northeastern Sichuan Basin:a case study fromWubaochang area

川东北地区侏罗系沙溪庙组浅层致密气具有投资成本低、见效快、分布广、资源量大、埋深浅等诸多优势,是一个高效的勘探开发对象。通过对川东北五宝场地区侏罗系沙溪庙组天然气与下伏烃源岩实地采集,进行了相关的天然气组分、碳同位素、镜质体反射率、显微组分以及总有机碳测定等地球化学实验,根据天然气和烃源岩样品分析,对川东北侏罗系沙溪庙组进行了气源讨论,并结合沙溪庙组典型成藏剖面和川东北致密气现有开发程度,对川东北侏罗系沙溪庙组典型成藏模式作出分析。结果表明:川东北地区侏罗系沙溪庙组天然气主要来自于下伏的侏罗系自流井组湖相烃源岩和三叠系须家河组煤系烃源岩。川东北地区侏罗系自流井组烃源岩为Ⅱ1—Ⅱ2型高成熟中等—好烃源岩,须家河组烃源岩为Ⅲ型过成熟烃源岩。川东北大巴山前缘的五宝场和渡口河地区具备良好的致密气成藏条件,是下一步浅层致密气的重点勘探地区。勘探重点应该以寻找沙溪庙组有利区带为主,同时增加下伏自流井组和须家河组的探井以获取更多的地质资料,以五宝场、渡口河地区为中心向外辐射扩大勘探开发范围。

The shallow tight gas of Jurassic Shaximiao Formation in northeastern Sichuan Basin has many advantages,such as low investment cost,quick effect,wide distribution,large amount of resources and shallow burial depth,so it is an efficient exploration and development object.Through the collection of natural gas of Jurassic Shaximiao Formation and underlying source rocks in Wubaochang area of northeastern Sichuan Basin,the natural gas components,carbon isotopes,vitrinite reflectance,microscopic components and total organic carbon content were determined.Combined with analysis of natural gas and source rock samples,the gas source of Jurassic Shaximiao Formation in northeastern Sichuan Basin was discussed.Combined with typical reservoir accumulation section of Shaximiao Formation and the present development degree of tight gas in northeastern Sichuan Basin,the typical reservoir accumulation model of Jurassic Shaximiao Formation in northeastern Sichuan Basin was analyzed.The results show that the natural gas of Jurassic Shaximiao Formation in northeastern Sichuan Basin mainly comes from the underlying lacustrine source rocks of Jurassic Ziliujing Formation and coal measure source rocks of Triassic Xujiahe Formation.The source rocks of Jurassic Ziliujing Formation in northeastern Sichuan Basin are typeⅡ1-Ⅱ2 high mature medium-good source rocks,and the source rocks of Xujiahe Formation are typeⅢover-mature source rocks.The Wubaochang and Dukouhe areas in the front margin of the Daba Mountain in northeastern Sichuan Basin have good conditions for tight gas accumulation,and are the key areas for next shallow tight gas exploration.The exploration should focus on finding favorable zones of Shaximiao Formation,increase the exploration wells of underlying Ziliujing Formation and Xujiahe Formation to obtain more geological data,and expand the exploration and development scope outwards withWubaochang and Dukouhe areas as the center.