氩离子抛光-环境扫描电镜在页岩纳米孔隙研究中的应用——以辽中凹陷JX地区沙一段为例

The application of argon ion polishing-environmental scanning electron microscopy to the research on shale nanometer-sized pores——Taking Sha-1 member in JX area as an example

微观孔隙结构是页岩气储层研究的重点,但传统扫描电镜无法识别机械抛光中造成的不规则形貌。利用氩离子抛光—场发射环境扫描电镜方法对辽中凹陷JX1-1地区沙一段(E_3s^1)页岩储层孔隙进行了研究。结果表明,该页岩形成于裂谷裂陷后热沉降背景下的半深湖—深湖环境,黏土矿物含量高,有机质丰富,决定了其孔隙以矿物基质孔中黏土矿物片间孔、黏土集合体内矿片间孔和有机质孔发育最好,油气地质意义最大;黏土矿物片间孔是片状的黏土矿物通过边缘和面、边缘和边缘、面和面之间的定向—半定向接触搭接形成,呈狭长的菱形、蜂窝状和不规则状,大小在0.5~5μm之间;黏土集合体内矿片间孔为黏土矿物在自身转化及压实作用中形成的,一般为弯曲的缝状孔,宽度介于30~500 nm范围内,长度数可达2~50 nm;页岩在热演化过程中,有机质大量向烃类转化,形成了大量的有机质孔,多呈片麻状、不规则状、凹坑状、椭圆状,大小在0.2~2μm之间。该研究对该区页岩气勘探层位选取、资源潜力评价和勘探开发具有一定的指导的意义。

The microscopic pore structure is the key to the study of shale reservoir. However,traditional scanning electron microscopy（ SEM） methods cannot identify the irregular morphology caused by mechanical polishing. Scanning electron microscopy combined argon ion polishing technology was taken to study the characteristics of shale reservoir pores of Member 1 of Shahejie Formation（ E_3s^1） located in JX1-1 area of Liaozhong Sag. The results show that pores among clay platelets,intraplatelet pores within clay aggregates and organic-matter pores are very rich in the area,and these types of pores are of great significance to oil-gas exporation due to the shale with high content of clay minerals and rich organic matter,which formed in semi deep-deep lake environment under the background of the thermal subsidence after rifting. Pores among clay platelets are formed by directional or semi-directional contact among edge and surface,edge and edge or surface and surface of laminated clay minerals,whose shapes are narrow rhomboid,honeycomb,and irregula with the size of 500 nm to 5 μm. The intraplatelet pores within clay aggregates are formed in the process of the transformation and compaction of clay minerals,whose shapes are usually curved slit with the width of 30 to 500 nm and the length of 2 to 50 μm. The organic-matter pores are from the process of the conversion from organic matters to the hydrocarbon under thermal evolution,whose shapes are gneissic,irregular,pitted and elliptical with the size of 100 nm to 2 μm. This study is of certain guiding significance to selecting target zones,evaluating resource potential and exploration and development of shale gas in this region.