安徽省宣城地区龙潭组页岩孔隙发育特征及其影响因素

Pore characteristic and its controlling factors of the shales in Permian Longtan Formation in Xuancheng area,Anhui Province,China

安徽省宣城地区上二叠统龙潭组页岩气资源潜力大,已有钻井揭示其页岩含气性差异大,页岩气赋存富集机理复杂。通过总有机碳含量分析、岩石热解实验、X衍射、低温液氮吸附、二氧化碳吸附和场发射扫描电镜观测等手段,研究宣城地区龙潭组页岩中孔隙的大小、结构及类型,探讨影响其孔隙发育的主要因素。研究表明:(1)宣城地区龙潭组页岩中孔隙主要为半开放型,并且存在一定量的细颈瓶孔。其中,矿物孔较发育,主要为微米孔,孔隙数量多;有机孔发育数量较少,孔径为纳米级—微米级。(2)龙潭组页岩BET比表面积为4.2601~10.3068 m^(2)/g,平均为7.4290 m^(2)/g。介孔+宏孔体积为0.0049~0.0179 cm^(3)/g,平均为0.0089 cm^(3)/g;微孔体积为0.0019~0.0038 cm^(3)/g,平均为0.0026 cm^(3)/g。孔径大于10 nm的孔隙是页岩孔隙体积的主要贡献者。(3)高演化、矿物含量差异大等使得宣城地区龙潭组页岩孔隙发育规律性变得复杂,TOC含量和矿物含量明显影响着宣城地区龙潭组页岩孔隙体积,但与孔隙比表面积没有明显线性相关性。在宣城地区龙潭组页岩气后续勘探开发中,应注重较高TOC含量、较高碳酸盐矿物含量和较低黏土矿物含量的页岩。

There is a great potential for shale gas resources of Longtan Formation in Xuancheng area,Anhui Province.However,it was revealed that the gas content of the Longtan shale varies greatly in several wells and the mechanism of shale gas accumulation was complex.Pore size distribution,structure and type of the Longtan shales in Xuancheng area were investigated by using total organic carbon content analyzer,rock pyrolysis,X-ray diffrac-tion,low pressure nitrogen gas adsorption and carbon dioxide gas adsorption and scanning electron microscopy.Besides,the controlling factors of pore development were discussed.The results show that:(1)The pores of Longtan Formation shale in Xuancheng area are mostly semi-open,and there is a certain amount of small neck pores.Mineral pores developed relatively in the shales which are mostly micron pores.A small number of organic pores distributed in the shales which the pore size is nanometer to micron.(2)The pore specific surface area in BET model of the Longtan shales in Xuancheng area ranges from 4.2601 m^(2)/g to 10.3068 m^(2)/g,with a mean of 7.4290 m^(2)/g.The sum of macropore volume and mesopore volume ranges from 0.0049 cm^(3)/g to 0.0179 cm^(3)/g,with a mean of 0.0089 cm^(3)/g.The micropore volume ranges from 0.0019 cm^(3)/g to 0.0038 cm^(3)/g,with a mean of 0.0026 cm^(3)/g.The main contributor of pore volume is the pores with pore diameter more than 10 nm.(3)The pore development regularity of Longtan Formation shale in Xuancheng area becomes complicated due to high evolution and large difference in mineral content.TOC content and mineral content obviously affect the pore volume of Longtan shale in Xuancheng area,but have no obvious linear relation with on the pore specific surface area.Further exploration and development of Longtan shale gas in Xuancheng area should focus on shale with higher TOC content,higher carbonate mineral content and lower clay mineral content.