## 2 Geological Settings  
The Linnan Subsag is located between the Linshang Fault and the Xiakou Fault in the southwest of the Huimin Sag, a secondary tectonic unit of the Jiyang Depression in the Bohai Bay Basin of China [39], which is a semigraben subsag with an axial northeast-east direction, north fault, and south overlap with an area of 3000 km\({}^{2}\)[40] (Figure 1a,b). The Linnan Subsag includes four structural units, which are the central uplift belt, Linnan Subsag belt, Xiakou fault belt, and Linnan slope belt, from north to south (Figure 1c). The main study area of this paper is the northern source region of the Linnan Subsag, which is located mainly between the central uplift belt and the Linnan Subsag belt. The sedimentary facies of the study area include the delta front, prodelta, semideep lake, and turbidity current subfacies (Figure 1d). Historically, the Linnan Subsag experienced two sedimentary stages, the Paleogene fault sag period and the Neogene fault-depression period, and the Paleogene strata of the Shahejie Formation (Es) and Dongying Formation (Ed), Neogene strata of the Guantao Formation (Ng) and Minghuazhen Formation (Nm), and Quaternary (Q) strata were deposited (Figure 1e). The third member of the Shahejie Formation is the most important exploration horizon at present, and Es\({}_{3}\)\({}^{3}\) is the main oil-bearing layer of tight oil in the Linnan Subsag. Under the influence of the Linshang fault activity, the Linnan Subsag produced a steep slope in the late sedimentary stage of Es\({}_{3}\)\({}^{3}\), which provided sufficient conditions for the collapse of the delta front and finally led to the development of many deep-water turbidity fan deposits [41]. There are 1-6 sets of sand groups from top to bottom, of which the 1 st and 3 rd sand groups are source rocks with organic-rich mudstone, whereas the 2 nd and 4-6 th sand groups are tight sandstone reservoir groups.  
There are two sets of sedimentary systems in Es\({}_{3}\)\({}^{3}\) in Linnan Subsag, which are the gravity flow sedimentary system corresponding to sand Group 2 of the deep-water slip turbidity sand body and the delta sedimentary system corresponding to sand Groups 4-6 of the delta front subfacies (Figure 2). Among them, the gravity flow sedimentary system developed turbidity current sedimentation, which has typical identification markers with normal bedding, bottom scouring surfaces, groove forms, thin interbedded sand-mud layers, and incomplete Bauma sequences. The delta sedimentary system in the study area has developed delta front subfacies sedimentation, and the lithology is mainly sandstone, siltstone, and claystone. In addition, the corresponding identification signs are sedimentary structures such as wavy bedding and cross-bedding. Moreover, the logging curve presents a funnel-bell composite shape [42; 43].  
Figure 1: Geological settings of study area: (**a**) Simplified location of the Bohai Bay Basin in China; (**b**) Simplified structural units of the Bohai Bay Basin and location of Linnan Subsag; (**c**) Simplified structural units and distribution of faults in the Linnan Subsag; (**d**) Sedimentary facies map of Es\({}_{3}\)\({}^{3}\) in the study area; (**e**) Stratigraphic columns of Es\({}_{3}\)\({}^{3}\) in the study area, Bohai Bay Basin. Es\({}_{3}\)\({}^{1}\), Es\({}_{3}\)\({}^{2}\), and Es\({}_{3}\)\({}^{3}\) are the lower, middle, and upper parts of the Third Member, respectively.  
Figure 2: Simplified sedimentary cross-section in Es\({}_{3}\)\({}^{3}\), Linnan Subsag (the cross-section location is shown in Figure 1c).