下扬子皖东南地区二叠系页岩储层特性及甲烷吸附能力

Characterization of Pores and Methane Sorption Capacity of Permian Shales in Southeast Anhui,Lower Yangtze Region

为深入研究皖东南地区二叠系页岩储层微观特征及其储气能力,选取2口钻井岩心样品进行负离子抛光—场发射扫描电子显微镜、氮吸附/脱附实验、甲烷吸附能力测定以及相关地球化学分析。结果表明,二叠系富Ⅱ—Ⅲ型有机质泥页岩石英等脆性矿物含量较高,存在晶间孔、粒间孔以及粒内孔、次生溶孔、有机质孔及微裂缝、构造缝等多种储集空间类型。采用He气法所测孔隙度为2.15%-6.10%、渗透率平均值为0.002 57×10^-3μm^2。该套页岩以中孔为主,含少量大孔和微孔,大多数的孔径分布在2-50nm之间。BJH孔容为3.30-11.23mm^3/g,其中,中孔和大孔孔容约占总孔容的80%;BET比表面积介于3.91-20.84m^2/g之间。T-图法计算微孔比表面积介于1.015-4.053m^2/g之间,中孔和微孔是页岩比表面积的主要贡献者。大量纳米级孔隙的发育及具有较大的比表面积,为页岩储层提供了良好的吸附聚气能力,实验模拟地层温压测定页岩甲烷最大吸附量达2.3-3.2m^3/t。说明研究区二叠系页岩具有良好的储集性能及甲烷吸附能力。

To investigate pore characteristics and methane sorption capacity of Permian shale reservoir in Southeast Anhui,Lower Yangtze region,eight core samples were selected for test including Ar-ion millingfield emission scanning electron microscope,N2 adsorption-desorption and methane sorption experiments and related geochemical analysis.The results show that the shales contain multi-types of pores including inter-granular pore,intra-granular pore,intra-crystalline pore,dissolved pore,organic pore and micro-cracks.The total porosity of our samples ranges from 2.15% to 6.10% and average permeability is 0.002 57×10^-3μm^2.The nanoscale pores mainly consist of meso-pores and small parts of micro-and macro-pores.The pore diameters mostly range from 2to 50 nm.The pore volume counted by BJH equation ranges from 3.30-11.23mm^3/g and the total surface area calculated by BET equation ranges from 3.91-20.84m^2/g.The micropore surface calculated by T-method ranges from 1.015-4.053m2/g.Meso-and micro-pores mainly contribute to the surface areas.These namopores and large surface area in the Permian organic-rich shales could provide good conditions for shale gas storage.The methane adsorption capacity is up to 2.3-3.2m^3/t at 27 MPa.This indicates that the Permian shales have relatively favorable storage condition for shale gas.