川中地区大安寨段页岩油储层孔隙微观形态研究

Study on pore morphology of Shale oil reservoir in Da'anzhai Member in central Sichuan Basin

大安寨段湖相页岩是四川盆地页岩油勘探的关键层。为了解其微观孔隙,使用氩离子抛光、扫描电镜和图像处理软件提取高分辨率电镜图像的孔隙,获取不同孔隙的孔径、圆度、伸长率等参数。结果显示:大安寨段黑色页岩中有2类7种常见孔隙,主要是黏土孔隙、石英/方解石晶内孔隙、粒缘孔隙和有机孔;不同孔隙类型形态差异大,有机质孔隙小且凸性值趋近1,黏土晶间孔隙、粒缘孔隙圆度凸性值小、伸长率大,方解石晶内孔隙大且圆度凸性较大。孔隙大小和形状受组分和压实作用控制:无机孔隙普遍大于有机孔,无机孔中脆性矿物孔径最大,呈多边形,而塑性矿物孔径小,呈伸长率大的片状。

The Da'anzhai Formation lacustrine shale is a key target for shale oil exploration in the Sichuan Basin.To understand its microscopic pore characteristics,this study used argon ion polishing,scanning electron microscopy,and image processing software to extract pores from high-resolution electron microscope images and obtain parameters such as pore diameter,roundness,and elongation ratio for different pores.The results indicate that the black shale of the Da'anzhai Formation contains two classes and seven common pore types,primarily clay pores,quartz/calcite crystal pores,grain-edge pores,and organic pores.Different pore types exhibit significant morphological differences,with organic pores being small with a roundness approaching 1,clay intercrystalline pores and grain-edge pores having small roundness convexity values and large elongation ratios,and calcite crystal pores being large with relatively large roundness convexity.Pore size and shape are controlled by composition and compaction:inorganic pores generally have larger diameters than organic pores,with inorganic pores in brittle minerals having the largest diameters,often polygonal,while inorganic pores in plastic minerals have smaller diameters and are often elongated.