龙马溪组岩相类型及其对孔隙特征的影响因素

Lithofacies Types of Longmaxi Formation and Its Influencing Factors on Pore Characteristics

以川南黔北地区下志留统龙马溪组下段页岩储层为研究对象,以全岩矿物分析为手段,结合岩芯薄片观察,划分出4种页岩岩相,其中,黏土质页岩岩相和混合页岩岩相是本研究区发育的主要岩相。基于扫描电镜、有机碳含量和低温氮气吸附实验,系统地分析了两种主要岩相孔隙结构特征。结果表明,黏土质页岩岩相储层中较大孔隙以细颈瓶状、开放型孔隙和半封闭孔为主,混合页岩岩相较大孔隙形态以开放型孔隙和部分半封闭孔为主,两种岩相较小孔隙形态多是半封闭孔。TOC有利于微孔和中孔的发育,黏土矿物发育有利于大孔的发育。由于黏土质页岩岩相的黏土矿物含量比混合页岩岩相高,TOC含量却比混合页岩岩相低,加上成岩作用影响,从而导致黏土质页岩岩相的大孔孔隙体积比混合页岩岩相大,微孔和中孔孔隙体积比混合页岩岩相小。

The main subjects of study for this paper are from Longmaxi Formation of Lower Silurian in northern Yunnan and Guizhou Province.Based on analysis of whole rock-mineral and observation of core slices,we divide shale lithofacies into 4 types of shale facies,in which the main developed lithofacies in the study area are the clayey shale facies and mixed shale facies.Based on scanning electron microscopy imaging and organic carbon content measurement,and the experiment of nitrogen adsorption at low temperature,we analyzed the pore structure characteristics of different shale facies.The results show that the larger pores in argillaceous shale facies reservoir are mainly flask-shaped pores,open pores and half-closed pores.The larger pore forms in mixed shale facies are mainly open pores with some half-closed pores;the smaller pores in the two facies are mostly half-closed pores.The content of TOC is favorable to the development of micropores and mesopores,while the content of argillaceous minerals is beneficial to the development of macropores.Because the clay mineral content of the clayey shale facies are higher than that of the mixed shale facies,as well as the effect of diagenesis,the macro-pore volume of the clayey shale facies is higher than that of the mixed shale facies,the pore volume of micro-pore and meso-pore is smaller than that of mixed shale facies.