鄂尔多斯盆地差异抬升对长7页岩孔隙的影响——以东南部甘泉地区和南部渭北隆起地区为例

The effect of differential uplift on pore development of Chang 7 shale in Ordos Basin:Case studies of Ganquan area and Weibei uplift area

为对比研究差异抬升对鄂尔多斯盆地延长组长7页岩孔隙的影响,分别选取了甘泉地区G127井和渭北隆起YW1井(浅地表)2组埋深相差较大的长7~3典型页岩样品,通过脉冲衰减渗透率测量、覆压孔隙度测量、氮气吸附实验及氩离子抛光—扫描电镜成像分析等方法对样品孔隙特征进行表征。结果表明:页岩储层孔隙均主要为纳米级,孔隙类型主要有粒间孔、粒内孔、微裂缝及少量有机质孔。其中,G127井有机质孔较发育,主要由于该区页岩所达最大埋深较深,样品热演化程度较高;而YW1井页岩裂缝较发育,这与盆地南部经历了强烈的构造抬升运动有关,致使YW1井页岩样品渗透率(1.13~4.24)×10^(-3)μm^2普遍高于G127井渗透率(0.013 5~0.663 0)×10^(-3)μm^2。2组页岩中小于10nm微孔和中孔提供了主要的比表面积,大于10nm的中孔和大孔对孔隙体积贡献较大,其中G127井页岩平均孔径及孔径峰值均较YW1井页岩小,这与其埋深较深导致压实作用更强有关。

To study the micro pore characteristics of Chang 7 shale in Ordos Basin,we selects two groups of different depths of Chang 7 shale samples from Well G127（smaller uplift）and Well YW1（larger uplift）,using Pulse attenuation permeability measurement,overburden pressure measurement,nitrogen adsorption experiment and Argon ion polishing scanning electron microscopy image analysis to characterize the pore.The results show that the pore size of shale reservoir is mainly nanoscale,and the main pore types are intergranular pore,intragranular pore,micro-fracture and a small amount of organic hole,of which organic hole is relatively well developed,which is related to the small amplitude of the uplift and the deeper burial depth of the shale.Meanwhile the fractures of Well YW1 shale which experienced strong tectonic uplift are more developed,so that the permeability of Well YW1 shale sample is generally higher than that of Well G127;Shale pore size distribution is complex,the pore shape is mainly composed of parallel plates,slit pores and ink bottle holes,which are open at both ends.Less than 10 nm micropores and mesopores provide the main specific surface area.Mesopores and macropores larger than 10 nm contribute greatly to pore volume.Based on the comparative study of uplifting effect on shale pore,this paper will provide reference for the exploration of shale gas and the delineation of favorable blocks in Ordos Basin.