)1 State Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum (Beijing), Beijing 102249, China; [EMAIL_ADDRESS] (L.R. )1 State Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum (Beijing), Beijing 102249, China; [EMAIL_ADDRESS] (L.R)1 State Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum (Beijing), Beijing 102249, China; [EMAIL_ADDRESS] (L.R. )1 State Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum (Beijing), Beijing 102249, China; [EMAIL_ADDRESS] (L.  
As the main oil-producing subsag in the Huimin Sag in the Jiyang Depression of the Bohai Bay Basin in China, the Linnan Subsag has great potential for tight oil resources, which are mainly distributed in the middle and lower parts of the third member and the upper part of the fourth member of the Paleogene Shahejie Formation [8; 9]. According to field exploration data from the Sinopec Shengli Oilfield, the tertiary reserves of Linnan Subsag are 1.4984 \(\times\) 10\({}^{8}\) t, the predicted reserves are 1.10 \(\times\) 10\({}^{8}\) t, and the unproduced proven reserves are 2766.23 \(\times\) 10\({}^{4}\) t. The data indicate a favorable potential for unconventional tight oil and gas resources. Among them, the predicted reserves of the lower third member of the Shahejie Formation (Es\({}_{3}\)) are 8465.2 \(\times\) 10\({}^{4}\) t, accounting for 64% of the overall predicted reserves in the Linnan Subsag. During the sedimentary period of Es\({}_{3}\), which was influenced by the uplift of the Linshang fault, two different sedimentary systems developed in the Linnan Subsag, namely, the turbidity current and delta front deposits. Although the reservoir position, depth, and physical properties of these two different sedimentary systems are similar, their oily properties are obviously different. Scholars have reported that the difference between the charging strength and the oil abundance of tight oil reservoirs is mainly controlled by the reservoir quality [10; 11; 12]. Past studies have shown that many geological factors affect the quality of tight sandstone reservoirs, including the sedimentary system, reservoir physical properties, and reservoir microscopic pore structure. The distribution and accumulation of tight oil and gas are closely related to the characteristics of the microscopic pore structure [13; 14; 15; 16]. The microscopic pore structure of a reservoir controls the oil and gas flow capacity and rate, which is the most critical factor affecting the oil-bearing and reservoir physical properties and accumulation of tight reservoirs [17; 18; 19; 20; 21; 22; 23]. Many scholars have confirmed the importance of micro/nanopore structures for the evaluation of unconventional reservoirs and the analysis of the oil-bearing properties of tight reservoirs [14; 24; 25; 26; 27]. Oiliness in tight reservoirs is a major and intuitive indicator of the reservoir quality and its corresponding heterogeneity. The heterogeneity and complexity of reservoirs, especially the micro/nanopore structure, affect the charging, migration, and accumulation of petroleum and ultimately manifests as differences in oil-bearing properties [27; 28; 29; 30; 31]. According to previous research results, the microscopic pore structure of a reservoir is clearly the core and key to the oil-bearing properties of tight reservoirs. At present, reservoir pore structure characterization can be carried out via nuclear magnetic resonance (NMR), high-pressure mercury injection (HPMI), low-temperature nitrogen adsorption, and other methods to study reservoir quality parameters such as the pore type, geometry, size distribution, and pore-throat connectivity, but the factors influencing the microscopic pore structure in tight reservoirs are not clear. Clarifying the characteristics of the microscopic pore structure of reservoirs and analyzing the influencing factors has an obvious guiding role in geological exploration and oil well development.