桂北中奥陶统升坪组页岩气储层特征:以溪水源剖面为例

Shale gas reservoir characteristics of the Middle Ordovician Shengping Formation in northern Guangxi:A case study of Xishuiyuan section at Wenqiao Town,Quanzhou County

为综合评价桂北地区中奥陶统升坪组页岩气储层特征,利用偏光显微镜、扫描电子显微镜、碳硫分析仪、X射线衍射仪、稳定同位素质谱仪、孔渗分析仪和有机质成熟度分析等检测方法,对广西全州县文桥镇栗水村溪水源剖面黑色页岩的有机质丰度、无机矿物组成、储集空间及物性特征等进行了探讨分析。结果表明:升坪组碳质页岩累计厚度约81 m,以Ⅰ—Ⅱ型干酪根为主,TOC值介于0.63%~3.04%之间,平均为2.04%;Ro值为3.52%~3.68%,平均为3.60%;页岩矿物成分主要有石英、长石、黄铁矿、硬石膏、白云石和方解石,脆性指数介于52.70~89.00之间,平均为73.31;黏土矿物以伊利石为主,伊/蒙混层次之,不含蒙脱石,指示了明显的蒙脱石向伊利石转换过程;孔隙类型主要为有机质铸模孔、粒间孔、晶间孔、溶蚀孔和微裂缝,孔隙度为1.0%~6.8%之间,平均为3.12%;渗透率介于0.001 3×10^(-3)μm^(2)~0.042 5×10^(-3)μm^(2)之间,平均为0.019 0×10^(-3)μm^(2)。通过与四川盆地和北美页岩气储层特征的对比分析,指出桂北地区中奥陶统升坪组中段页岩气勘探潜力较大。

In order to comprehensively evaluate the shale gas reservoir characteristics of the Middle Ordovician Shengping Formation in northern Guangxi,the organic matter abundance,inorganic mineral composition,reservoir space and physical property of the Xishuiyuan section in Lishui village,Wenqiao Town,Quanzhou County,Guangxi are discussed and analyzed by means of polarizing microscope,scanning electron microscope,carbon and sulphur analyzer,X-ray diffraction,stable isotope mass spectrometer,pore and permeability analyzer and organic matter maturity.It shows that the carbonaceous shale of Shengping Formation has a thickness of 81 m,with typesⅠandⅡkerogen.The TOC value ranges from 0.63%to 3.04%,with the average value 2.04%.The Ro value is 3.52%~3.68%,with an average of 3.60%.The mineral composition of Shengping Formation shale mainly includes quartz,feldspar,pyrite,anhydrite,dolomite and calcite.The brittleness index ranges from 52.70 to 89.00,with the average value 73.31.Clay minerals are mainly illite,with mixed illite/montmorillonite layers,and no montmorillonite,indicating an obvious conversion process from montmorillonite to illite.The pore types are mainly organic mold pores,intergranular pores,intercrystalline pores,dissolution pores and microcracks.The porosity ranges from 1.0%to 6.8%,with an average of 3.12%.The permeability ranges from 0.0013×10^(-3)µm^(2) to 0.0425×10^(-3)µm2,with the average value 0.019×10^(-3)µm^(2).Through comparative analysis of shale gas reservoir characteristics with those of Sichuan Basin and North America,it is pointed out that the middle member of the Middle Ordovician Shengping Formaiton in northern Guangxi has the large shale gas exploration potential.