## 5 Discussion
### Stress Difference and Stress Difference Coefficient  
In shale oil reservoirs with natural fractures, the propagation of artificial fractures is not only related to the stress state but also closely connected with the horizontal stress difference (\(\Delta\sigma\)) and horizontal stress difference coefficient (\(K_{\text{h}}\)). These two parameters comprehensively determine whether hydraulic fractures and natural fractures can jointly form beneficial fracture network systems [44]. The following formulas represent the horizontal stress difference and horizontal stress difference coefficient, respectively:  
\[\Delta\sigma=\sigma_{\text{{hmax}}}-\sigma_{\text{{hmin}}} \tag{10}\]  
Figure 16: Frequency distribution of in situ stress. (**A**) Minimum horizontal principal stress; (**B**) maximum horizontal principal stress. Figure 17: The orientation of the horizontal principal stress of P\({}_{1}\)f\({}^{1}\). (**A**) Minimum horizontal principal stress; (**B**) maximum horizontal principal stress. \[K_{h}=\frac{\sigma_{hmax}-\sigma_{hmin}}{\sigma_{hmin}} \tag{11}\]  
where \(\Delta\sigma\) Is the horizontal stress difference; \(K_{h}\) is the horizontal stress difference coefficient; \(\sigma_{hmax}\) is the maximum horizontal stress; and \(\sigma_{hmin}\) is the horizontal minimum stress. Figure 18: In situ stress, mechanical modulus and related parameters on a 2D cross-section. (**A**) Minimum horizontal principal stress; (**B**) maximum horizontal principal stress; (**C**) Young’s modulus; (**D**) Poisson’s ratio; (**E**) Stress difference; (**F**). Stress difference coefficient. The location is shown in Figure 2(b–b). Figure 20 shows the planar distribution of the horizontal stress difference in \(\mathrm{P_{1}f^{2}}\) and \(\mathrm{P_{1}f^{3}}\). The horizontal stress difference is generally greater than 12 MPa, mainly distributed between 16 and 20 MPa. There is a correlation between horizontal stress difference and burial depth. As shown in Figure 10A, the terrain in the study area is higher in the north and lower in the south. In contrast, the horizontal stress difference coefficient, lower in the north and higher in the south, displays an opposite characteristic in the research area. Therefore, as depth increases, the stress difference exhibits an upward trend. The magnitude of the stress difference is directly proportional to depth. Conversely, the shallower the formation, the smaller the magnitude of horizontal stress difference. As shown in Figure 10B, there are two types of faults with different orientations in the study area. Some are northeast oriented, while others are southeast oriented. As illustrated in Figure 20, there is an increase in horizontal stress difference near the faults. In addition, the geomechanical parameters also influence the horizontal stress difference to some degree. In areas where [PERSON]'s modulus and [PERSON]'s ratio are both high, the horizontal stress difference shows high numerical values (Figures 18, 21 and 22). Therefore, the horizontal stress difference is positively correlated with [PERSON]'s modulus and [PERSON]'s ratio. Figure 19: Planar distribution of dip azimuth in the research area. The horizontal stress difference coefficients, concentrated between 0.17 and 0.23, are generally greater than 0.14 (Figure 23). The horizontal stress difference coefficient is not significantly affected by burial depth. There is no evident correlation between burial depth and the stress difference coefficient (Figure 18). However, faults may affect the magnitude of the stress difference coefficient. Figure 21: Planar distribution of [PERSON]’s ratio of different layers. (**A**) [PERSON]’s ratio of P1\(\ell\); (**B**) [PERSON]’s ratio of P1\(\ell\). Figure 22: Planar distribution of [PERSON]’s modulus of different layers. (**A**) [PERSON]’s modulus of P1\(\ell\); (**B**) [PERSON]’s modulus of P1\(\ell\). of stress difference coefficients. The stress difference coefficient increases when there is a fault nearby (Figure 23).