## 4 Results  
### Fracture Characteristics Across Diverse Scales  
The Chang 7 member of the Yanchang Formation in the Ordos Basin is distinguished by the development of tight sandstone [16; 17]. Observations of outcrops in the Xi 233 well area and its surrounding regions reveal that the development is predominantly characterized by structural fractures (Figure 2A). Shear fractures typically display stable occurrences, extensive lengths, relatively planar surfaces, and substantial inclination angles, with some occurring as conjugate pairs [52; 53]. The fractures observed in the target layer and its surrounding areas are predominantly high-angle shear fractures and vertical fractures, reflecting pronounced shear effects (Figure 2B). The angles of the conjugate fractures are generally around 60\({}^{\circ}\) (Figure 2C,D). Multiple periods of tectonic activity in the region have resulted in intersecting fractures visible in field outcrops (Figure 2A). Some fractures are significantly filled with calcite, pyrite, and mud, occupying space within oil and gas reservoirs (Figure 2E,F). However, the limited number of filled fractures in the region minimally impacts subsequent oil and gas accumulation [22]. Based on field outcrop observations and rock core fracture analysis, fractures in the study area are categorized into three types: structural fractures, bedding fractures, and diagenetic fractures [54; 55]. 1. Structural fracture: Fractures formed under structural stress [21]. The Chang 7 member of the Yanchang Formation was deposited during the Indochina Movement, and the compressional forces from this tectonic event induced the formation of structural fractures. Fractures resulting from tectonic activity significantly alter the pore structure of the rock, increasing permeability, which facilitates the migration and accumulation of hydrocarbons. The high-angle shear fractures observed in the cores from the research area are elongated, with some core cross-sections exhibiting slickenside, indicating slippage at those locations (Figure 3A-C). 2. Bedding fracture: A fracture formed by tectonic stress superimposed on pre-existing diagenetic fractures [21; 52]. The research area exhibits numerous visible bedding fractures, which are often concentrated and densely developed (Figure 3D,E). 3. Diagenetic fracture: A fracture formed during sedimentation or diagenesis, typically characterized by low angles [52]. Diagenetic processes, occurring under high temperature and pressure, can also generate fractures in the rock. Chemical and physical changes such as mineral dissolution, cement precipitation, or expansion of the rock may lead to fracture formation. These processes reduce rock strength, making it more susceptible to fracturing, while also affecting the rock's reservoir capacity. These fractures often occur at lithological boundaries and are visible in the study area but have a limited distribution (Figure 3F). By observing and describing the fractures in the rock core, the length, opening, dip angle, and filling degree of the structural fractures were statistically analyzed [55]. (1) Fracture length  
Fracture lengths in the rock core are primarily distributed across three intervals: 10-20 cm, 20-30 cm, and 40-50 cm, accounting for 17%, 42%, and 15%, respectively (Figure 4A). Figure 3: Fracture development characteristics in rock cores. (**A,B**) High-angle structural fractures; (**C**) slickenside; (**D,E**) horizontal bedding fractures; (**F**) diagenetic fractures caused by lithological interface changes. Figure 2: Detailed analysis of fracture development characteristics in field outcrops. (**A**) A network system composed of multiple high-angle shear fractures; (**B**) a single shear fracture extending over considerable distances; (**C,D**) the angles of the conjugate shear fractures are 62\({}^{\circ}\) and 54\({}^{\circ}\), respectively; (**E**) the fracture-filling material is calcite; (**F**) the filling material within the fracture network system is pyrite.