Abstract: Based on casting thin sections and FE-SEM (field emission scanning electron microscope), the reservoir space of tight sandstone in the 3rd member of the Hetaoyuan Formation in the Biyang sag is divided into three types, including intergranular pores, intragranular pores and fractures. The former two, intergranular pores and intragranular pores, are primary reservoir space. According to the mineral composition, the intergranular pores are divided into quartz and feldspar intergranular pores, quartz and feldspar grain-boundary pores, and intergranular carbonate pores; the intragranular pores are divided into dissolved quartz and feldspar pores, intragranular carbonate pores and intercrystalline clay pores, which are relatively developed between 3023 m and 3035 m. Theses pore types are quantitatively calibrated based on a highresolution and large-view FE-SEM splicing technology. The results show that the surface porosity of the tight sandstone in the 3rd member of Hetaoyuan Formation is 3.75%, of which intergranular pores, intragranular pores and fractures account for 2.35%, 1.38% and 0.02%, respectively. In various types of reservoirs, the pore diameters have some differences, the intergranular pores of quartz and feldspar mainly ranging from 50 to 100 nm account for 42.4% and 30% respectively, and the grain-boundary quartz and feldspar pores mostly from 100 to 200 nm account for 30% each. Although the intergranular pores larger than 1000 nm account for less than 6%, they contribute more to total pore volume, of which the intergranular quartz and feldspar pores larger than 1000nm account for 95% of each pore volume. The intragranular pores in the range of 100 to 200 nm are dominant; quartz and feldspar dissolution pores are slight different from other types, and the pores between 200 and 500 nm are dominant, and account for more than 35% of each total pore volume.

Key words: quantitative characterization, reservoir space type, FE-SEM, large-view splicing, 3rd member of Hetaoyuan Formation, Biyang sag