## 4 Results
### Fracture Characteristics Across Diverse Scales
(2) Fracture aperture  
The aperture of fractures is a crucial statistical parameter for characterizing them [52]. Fracture width significantly affects oil and gas migration and seepage. Observations and statistical results indicate that the fracture width in the core well primarily ranges from 0.05 to 0.5 mm (Figure 4B). (3) Fracture dip  
Due to the minimal inclination of the observed well, its impact on the fracture dip angle is negligible [5]. Consequently, the angle between the fracture and the wellbore axis can be considered the true dip angle. Based on the inclination angle, fractures can be categorized as vertical (75-90\({}^{\circ}\)), high-angle (45-75\({}^{\circ}\)), low-angle (15-45\({}^{\circ}\)), and horizontal (0-15\({}^{\circ}\)). Among these, high-angle and vertical fractures are predominant in the target layer of the core well (Figure 4C). (4) Fracture filling degree  
The degree of fracture filling, also referred to as fracture effectiveness, varies with the amount of filling material present [20]. Generally, fractures with minimal or no filling material exhibit higher effectiveness, whereas those with significant filling material have reduced effectiveness. In the cores, the overall degree of filling is relatively low, with most fractures remaining unfilled and only a small proportion being either filled or partially filled (Figure 4D). Microscopic fracture identification focuses on fractures with apertures less than 0.1 mm, observable through thin sections and scanning electron microscopy [23; 40]. Observations of rock thin sections and scanning electron microscopy reveal a significant number of microfractures in the Chang 7 member of the Yanchang Formation, predominantly intragranular, intergranular, and transgranular fractures (Figure 5A-F). Despite their small size, these fractures play a critical role in subsequent dissolution processes. Intragranular and intergranular fractures can develop secondary pores through dissolution processes [40; 55]. Additionally, these fractures contain minimal filling material, making them effective storage spaces and significantly enhancing the physical properties of tight sandstone reservoirs [56]. Figure 4: Histogram representing fracture development in rock cores. (**A**) Characteristics of fracture length. (**B**) Features of fracture aperture. (**C**) Aspects of fracture dip. (**D**) Details of fracture filling degree. Imaging logging is effective in identifying fractures but may also detect pseudo-fractures, such as induced fractures and layer interfaces [15; 18]. Therefore, it is crucial to differentiate between genuine fractures and pseudo-fractures. Imaging logging can identify both high-conductivity and high-resistance fractures, and roughly determine their dip angles [15; 18]. Imaging logging data from the Xi 233 well area indicate that fractures in the Yanchang Formation are well-developed, particularly in the Chang 7 member, where high-angle fractures are predominant. Among the developed fractures, high-conductivity fractures are more common than high-resistance fractures, suggesting that most fractures are unfilled, consistent with field and core observations (Figure 6A,B). Additionally, each well in Chang 7 of the study area contains varying numbers of pseudo-fractures alongside natural fractures (Figure 6C-E). Figure 5: Microscopic characteristics of fracture development. (**A**) Transgranular fractures; (**B**) intergranular fractures; (**C**) intragranular fractures; (**D**) long columnar dolomite, development of intergranular fractures and dissolution pores; (**E**) microparticle quartz is concentrated and distributed, with intergranular fractures, shell-shaped fractures, and dissolution pores developed; (**F**) flake- and ribbon-shaped illite is distributed directionally, exhibiting well-developed pores and fractures. Figure 6: Characterization of various fractures using imaging logging. (**A**) High-resistance fractures; (**B**) high-conductivity fractures; (**C**) induced fractures; (**D**) small fault; (**E**) nodules.