## 4 Discussion
### Effect of Elastic Modulus  
Keeping other parameters constant, the ratio of elastic modulus between the interlayer and reservoir is set to 1.5, 2, 2.5, 3, and 3.5. The simulation results are shown in Figures 12 and 13.  
Figure 11: Illustration of the relationship between fracture width and half-length. (**a**) Relationship between width and half-length of the edge fracture. (**b**) Relationship between width and half-length of the mid fracture.  
Figure 10: Illustration of the relationship between fracture width and height. (**a**) Relationship between width and height of the edge fracture. (**b**) Relationship between width and height of the mid fracture.  
Figure 12 illustrates the relationship between the width and height of the edge and mid fractures under different elastic modulus ratios. It can be observed that as the elastic modulus ratio increases, the maximum width of the edge fracture decreases, and the differences between adjacent curves decrease. If the elastic modulus ratio continues to increase, the maximum width of the edge fracture may tend towards a constant value. The elastic modulus ratio at which the maximum width of the mid fracture stabilizes is reached relatively quickly. When the elastic modulus ratio is 1.5, the maximum width of the mid fracture is at its minimum value, and there is little difference in the maximum width among the other four cases.  
Figure 13 depicts the relationship between the width of the edge and mid fractures and their half-lengths under different elastic modulus ratios. It can be observed that under different elastic modulus ratios, the width of the edge fracture is negatively correlated with the half-length. The smaller the width, the larger the half-length, and the rate of decrease in fracture width decreases. Meanwhile, the increment of fracture half-length remains almost stable. For the mid fracture, when the elastic modulus ratio is 1.5, the fracture  
Figure 12: Illustration of the relationship between fracture width and height. (**a**) Relationship between width and height of the edge fracture. (**b**) Relationship between width and height of the mid fracture.  
Figure 13: Illustration of the relationship between fracture width and half-length. (**a**) Relationship between width and half-length of the edge fracture. (**b**) Relationship between width and half-length of the mid fracture.  
width initially increases and then decreases with the increase in half-length. There is little difference in the width-half-length curve among the other four cases, and as the fracture width increases, the fracture half-length decreases.  
As the elastic modulus ratio increases, the influence on the fractures becomes more significant. Increasing the ratio of elastic modulus will inhibit the extension of cracks in the vertical direction. The expansion of cracks in the vertical direction is impeded. Under the condition that the amount of fracturing fluid injection remains constant, this will cause the cracks to expand forward and increase the half-length of the cracks. The increase in half-length of the edge fracture and the decrease in the degree of fracture propagation are quite noticeable. The half-length of the mid fracture decreases but gradually approaches a stable value, while the degree of fracture propagation increases. However, the overall degree of fracture propagation decreases with the increase in the elastic modulus ratio, and the pore pressure in the model increases with the increase in the elastic modulus ratio. When the elastic modulus ratio is two, the half-length of the edge and mid fracture are comparable, and the degree of fracture propagation is relatively good.