中国南方海相页岩孔隙结构特征

我国南方古生界页岩成熟度高,页岩储层孔隙、裂隙类型多样,微米—纳米级孔隙发育。正确认识页岩孔隙特征是研究上述地区页岩气赋存状态,储层性质与流体间相互作用,页岩吸附性、渗透性、孔隙性和气体运移等的基础。为此,采用观察描述和物理测试两类方法对南方海相页岩孔隙特征进行了研究:前者通过手标本、光学显微镜、扫描电镜、核磁共振光谱学法、小角度X射线散射法等手段直观描述页岩孔隙的几何形态、连通性和充填情况,统计孔隙优势方向和密度,拍摄照片等,以确定页岩成因类型;后者通过He孔隙率测定、压汞实验、低温液氮吸附、低温CO2吸附等方法定量测试页岩孔容、孔径大小及其分布、孔隙结构、比表面积等,以评价页岩含气性。结果表明:该区古生界页岩储层中纳米级孔隙以干酪根纳米孔、颗粒间纳米孔、矿物晶间纳米孔、溶蚀纳米孔为主,喉道呈席状、弯曲片状,孔隙直径介于10～1 000nm,主体范围为30～100nm,纳米级孔隙是致密储层连通性储集空间的主体;按孔径大小,将页岩储集空间分为5种类型:裂隙(孔径大于10 000nm)、大孔(孔径介于1 000～10 000nm)、中孔(孔径介于100～1 000nm)、过渡孔(孔径介于10～100nm)、微孔(孔径小于10nm)。

Characteristics of pore structure of marine shales in South China

The Paleozoic shales in South China are of high maturity and in the shale formations there are multiple types of pores and fissures,particularly well-developed micro-and nano-scale pores.A correct understanding of pore features is the basis of the study of shale gas storage,interaction between reservoir properties and fluids,adsorption,permeability,porosity and gas migration.Observation and physical test were integrated to study the pore features of marine shales in South China.The observation methods include visual inspection,optical microscope,SEM,NMR spectroscopy,and small-angle X-ray scattering.They were used to describe the geometry,connectivity and fillings of pores,to count the dominant azimuth and density of pores,and to take photographs.All these data were used to determine the genetic types of shales.The physical tests include the Helium porosity test,mercury injection,low temperature liquid nitrogen adsorption,low temperature CO2 adsorption,etc.They were used to measure pore volume,size and distribution of pore diameter,pore structure,and specific surface area.All these data were used to evaluate the gas-bearing capacity of shales.The following conclusions are drawn.The nanopores in the shale formations are dominated by intra-kerogen,intergranular,intercrystalline and dissolution nanopores.Their pore throats are sheet-like or curved leaf-like and pore diameters are in the range of 10-1000 nm.The nanopores(pore diameter: 30-100 nm) are the main part of connected reservoir space of tight reservoirs.Shale reservoir space can be classified into 5 types according to pore diameters,namely fissures(pore diameter:>10000 nm),macropores(pore diameter: 1000-10000 nm),mesopores(pore diameter: 100-1000 nm),transient pores(pore diameter: 10-100 nm),and micropores(pore diameter:<10 nm).