华北过渡相页岩气储层微观孔隙结构特征:以山西省文水地区为例

Characteristics of micro-scale pore structures of shale gas reservoirs in transitional facies of north china:a case study of Wenshui Area in Shanxi Province

为表征过渡相页岩气储层纳米级孔隙发育特征,以山西省文水地区山西组与太原组煤系页岩为研究对象,采用高分辨率成像技术对页岩储层孔裂隙系统发育情况进行观察;利用低温氮吸附实验对页岩气储层孔隙结构加以表征。扫描电镜下页岩孔径多小于1μm,有机质孔含量不多,粘土矿物晶间孔、黄铁矿晶间孔等矿物基质孔较为发育,粒间孔少见。低温氮吸附实验表明,山西组页岩BET比表面积与总孔体积平均为5.4762m^2/g与0.0088cm^3/g,太原组页岩分别为6.7462m^2/g和0.0102cm^3/g,孔径小于10nm的微孔是比表面积的主要贡献者,中孔孔隙体积在总孔体积中占明显优势。BJH孔径分布曲线可分为两类,一类于2.5nm,4nm,10nm处有明显峰值;第二类除具有前者三个峰值外,于90nm处有相对较弱的峰值出现,该类样品同时具有相对较低的比表面积与总孔体积。

In order to characterize the features of nanometer-scale pores in shale gas reservoirs of transitional facies,the study assessed the coal shale from Shanxi Formation and Taiyuan Formation in Shanxi province.The development of pores and fissures system in shale gas reservoirs was observed by high resolution imaging technology,and the pore structures of shale gas reservoirs were characterized from the low temperature nitrogen adsorption experiment.The major pore width is less than 1μm in the SEM images.The content of organic pores is not high,and the mineral matrix pores such as clay mineral intercrystalline pores and pyrite intercrystalline pores have a relatively high content,but the interparticle pores were rare to see.The low temperature nitrogen adsorption experiment turned out that the BET surface area and pore volume of the shale in Shanxi Formation are 6.7462 m^2/g and 0.0102 cm^3/g,and which are 5.4762 m^2/g and 0.0088 cm^3/g in Taiyuan Formation.The pores with width less than 10 nm contributed the major surface area,and the mesopores comprised the main part of total pore volume.The BJH pore width distribution curve were divided into two types,one of which appeared three peaks in 2.5nm,4nm and 10nm;however,the other appeared another weaker peak in 90 nm.It is found that the samples within the second type of the curve have relatively low surface area and pore volume.