渝东南地区黑色页岩中粘土矿物特征兼论其对储层物性的影响——以彭水县鹿角剖面为例

为探索渝东南地区下志留统龙马溪组黑色页岩中粘土矿物特征及其与储层物性的关系,在综合前人对含油气盆地粘土矿物分析的基础上,以重庆市彭水县鹿角剖面为例,深入分析了鹿角剖面黑色页岩粘土矿物组合与分布特征、粘土矿物的形成机理及其控制因素以及粘土矿物对孔隙度和渗透率的影响。结果表明,一方面根据古盐度的计算,龙马溪组上部古水介质含盐度较低,下部较高,具有上淡下咸的特点;另一方面该套黑色页岩属于晚成岩阶段B期。储层中粘土矿物的类型、数量及其分布特征等对储层孔渗条件具有一定的控制作用。伊利石(含伊/蒙有序混层矿物)含量与孔隙度有弱正相关关系,与渗透率呈负相关关系,原因可能是成岩伊利石不断生长,一方面由于其体积减小使得显微孔隙体积有所增加,但另一方面,由于自生伊利石晶体细小,使得页岩粒间孔隙遭到不同程度的破坏,致使平均孔隙半径变小,渗透率变差。绿泥石含量与孔隙度呈现微弱的正相关关系,而与渗透率呈现较好的正相关关系。这是由于成岩绿泥石主要来源于长石溶解或蚀变形成的高岭石的转化,因此,绿泥石与孔隙度和渗透率的关系可能反映其与页岩中长石矿物的含量有关。

Clay Minerals of Black Shale and Their Effects on Physical Properties of Shale Gas Reservoirs in the Southeast of Chongqing: A Case Study from Lujiao Outcrop Section in Pengshui, Chongqing

In order to search after clay minerals of black shale and their effects on physical properties of shale gas reservoirs in the southeast of Chongqing,combination and distribution characteristic,formation mechanism and controlling factors of clay minerals and their effect on porosity and permeability are discussed in detail based on the knowledge of previous studies on clay minerals in petroliferous basins and taking Lujiao outcrop section in Pengshui County for example.Then it draws a conclusion that the combination of clay minerals in Lujiao section is I+C+I/S and the formation is controlled by palaeoenvironment and diagenesis which on one hand,the palaeosalinity is higher in the bottom and becomes lower in the up part,on the other hand,the black shale is in the B stage of late diagenesis.It has been discovered that type,quantity and distribution character of clay minerals are closely related to porosity and permeability of shale gas reservoirs.Exactly speaking,the growth of illite in the diagenesis can increase the porosity in some extent but will lose some permeability;chlorite has a positive correlation with porosity and permeability,which may be resulted from the detrital feldspars.