吴起-志丹地区长7致密砂岩储层孔隙结构特征及影响因素研究

Pore structure characteristics and influencing factors of Chang 7 shale oil sandstone reservoir in Wuqi-Zhidan area

运用高压压汞、扫描电镜、薄片鉴定等方法,对吴起-志丹地区长7致密砂岩储层孔隙结构特征及影响因素进行分析。结果表明,吴起-志丹地区长7致密砂岩储层平均孔隙度为7.5%,平均渗透率为0.13×10^(-3)μm^(2),整体物性较差,以特低孔-超低渗储层为主,其中,长71亚段物性比长72亚段好;区内孔隙类型主要为粒间孔和溶蚀孔,喉道类型以缩颈型喉道和片状/弯片状喉道为主;结合物性特征及高压压汞实验参数,将孔隙结构由好到差划分为三类,区内以Ⅱ类和Ⅲ类孔隙结构为主,其中,长71亚段孔隙结构优于长72亚段;储层品质指数与中值半径及分选系数具有良好的相关性;沉积作用对孔隙结构具有先天控制作用,成岩作用是影响孔隙结构的决定性因素,其中溶蚀作用对于储层孔隙结构具有一定的改善作用。

Using high-pressure mercury intrusion,scanning electron microscopy,thin section identification and other methods,the pore structure characteristics and influencing factors of Chang 7 shale oil sandstone in Wuqi-Zhidan area were analyzed.The results show that the Chang 7 shale oil sandstone reservoir has an average porosity of 7.5%,an average permeability of 0.13×10^(-3)μm^(2),and is dominated by ultra-low porosity-ultra-low permeability reservoirs.The Chang 7 shale oil sandstone reservoir has poor physical properties,and the Chang 71 has better physical properties than Chang 72.The pore types in the area are mainly intergranular pore and dissolution pore,and throat types are mainly constricted throats and sheet throats.Combining the physical properties and the experimental parameters of high-pressure mercury intrusion,the pore structure is divided into type I,type II,and type III from the best to the second,and the research area is dominated by type II and type III.Among them,the pore structure of Chang 71 is better than that of Chang 72.The reservoir quality index has a good correlation with the median radius and sorting coefficient.The sedimentation has a congenital control on pore structure.Diagenesis is the decisive factor affecting the pore structure,and the dissolution plays a second role in improving the pore structure of the reservoir.