鄂尔多斯盆地陕北地区长7段页岩油储层微观特征及控制因素

Microscopic characteristics and controlling factors of Chang 7 Member shale oil reservoir in northern Shaanxi area,Ordos Basin

鄂尔多斯盆地陕北地区长7段蕴藏着丰富的页岩油资源。通过扫描电镜、微米CT、二维FIB-SEM测试等高精度孔隙分析技术手段,结合大量岩心、薄片、测井等资料,对该区长7段多期砂岩叠置型页岩油储层的微观特征进行精细刻画,讨论其主要控制因素。结果表明:研究区长7段页岩油储层孔隙以微米孔为主,半径为2.0~50μm,喉道半径为0.3~13μm,其孔喉为微米—纳米级与微米级喉道连通形成的众多簇状孔喉单元;其孔隙度分布在3.0%~13.0%之间,平均孔隙度为7.0%,渗透率在(0.02~0.30)×10^(−3)μm^(2)之间,平均渗透率为0.15×10^(−3)μm^(2);其压汞曲线特征表现为排驱压力低、退汞效率高、粗喉道占比高。研究区长7段页岩油储层粒度细、塑性组分含量高、早期压实作用强烈、黏土矿物和碳酸盐胶结强烈是造成其孔隙减孔的主要因素,而溶蚀作用和绿泥石膜的保护作用具有一定的增孔效应。陕北地区长7段页岩油储层与庆城地区类比表明其具有Ⅰ类页岩油勘探开发的潜力。

Rich shale oil resources are developed in the Chang 7 Member of the Mesozoic Triassic Yanchang Formation in northern Shaanxi area,Ordos Basin.This paper mainly uses core,thin section,well logging and other data,focusing on high-precision pore analysis techniques such as scanning electron microscopy,micro-CT,two-dimensional FIB-SEM testing,etc.to finely portray the micro-features and to discuss its main controlling factors.The pores of the Chang 7 shale oil reservoir in the study area are mainly micro-pores with a radius of 2.0-50μm and a throat radius of 0.3-13μm.Numerous clustered pore-throat units are formed by micro-nanolevel and micro-level throat connecting micro-level pores.The porosity is distributed between 3.0%and 13.0%,and the average porosity is 7.0%.The permeability is between 0.02×10^(−3)μm^(2) and 0.30×10^(−3)μm^(2),the average permeability is 0.15×10^(−3)μm^(2).The mercury injection curve is characterized by low displacement pressure,high mercury removal efficiency,and high proportion of thick throat.The Chang 7 Member shale oil reservoir in the study area has fine grain size and high content of plastic components.The main factors that cause its pores to decrease are the strong early compaction and the strong cementation of clay minerals and carbonates.The dissolution and the protective effect of the chlorite film have a certain pore-enhancing effect.The potential for Type I exploration and development of Chang 7 Member shale in northern Shaanxi area is huge.Compared with Qingcheng area,the classⅠmulti-stage superimposed sandstone reservoir of shale oil has great exploration and development potential in northern Shaanxi area.