Abstract: The study of micropore structure in reservoirs is of great significance for oil and gas exploration and development. This article uses experimental methods such as nitrogen adsorption, blue-dye thin section observation, scanning electron microscopy (SEM) observation, X-ray diffraction (XRD), and nuclear magnetic resonance to study the micropore structure of the tight sandstone in the Yanchang Formation 7 Member of the Zhijing-Ansai area. The pore structure parameters and distribution are calculated, and the types of micropores are analyzed. The mineral composition, particle size, and sorting parameters that affect the development of micropores are discussed. The results show that the lithology of the Chang 7 Member is mainly feldspar sandstone. The micropore structure of tight sandstone is complex, mainly existing in the form of clay intergranular dissolution pores, feldspar dissolution pores, etc. The Chang 7 Member mainly develops small pore throats, with an average pore volume of 6.19 × 10-3 mL/g, indicating poor pore development. In the sandstone samples of the Chang 7 oil layer, the average BET (Brunauer-Emmett-Teller) specific surface area of the Chang 7 Member is 4.252 m2/g, the average total pore volume is 0.018 3 mL/g, and the average maximum pore size is 185.9 nm. The sandstone pores are mainly mesopores, followed by macropores and micropores.

Key words: Ordos basin, Chang 7 Member, tight sandstone, nitrogen adsorption, microscopic pore research