## 4 Experimental Results  
### Shale Fracture Morphology  
In this experiment, the effects of differential ground stress, fracturing fluid displacement, and hydration time on the expansion of seam height in marine and continental shales were considered. In order to present the fracture directions on six surfaces at the same time, the method of making specimen crease diagrams was used, as shown in Figure 6. A comparison of shale fracture morphology under different fracturing conditions is shown in Figure 7.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Samples** & **Number** & \(\sigma_{H}\) & \(\sigma_{V}\) & \(\sigma_{h}\) & \(\mu\) & \(Q\) & **Hydration Time** \\  & & /MPa & /MPa & /MPa & /MPa & /mPa\(\cdot\)s & /mL\(\cdot\)min\({}^{-1}\) & /h \\ \hline \multirow{4}{*}{Marine shale} & S-1 & 20 & 15 & 15 & 3 & 10 & 0 \\  & S-2 & 20 & 15 & 15 & 3 & 3 & 0 \\  & S-3 & 20 & 15 & 15 & 3 & 10 & 2 \\  & S-4 & 20 & 15 & 10 & 3 & 10 & 0 \\ \hline \multirow{4}{*}{Continental shale} & Y-1 & 20 & 15 & 15 & 3 & 10 & 0 \\  & Y-2 & 20 & 15 & 15 & 3 & 3 & 0 \\ \cline{1-1}  & Y-3 & 20 & 15 & 15 & 3 & 10 & 2 \\ \cline{1-1}  & Y-4 & 20 & 15 & 10 & 3 & 10 & 0 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Parameter settings for indoor fracturing simulation experiments.  
Figure 6: Unfolded 3D graphics and fold-out diagram of a specimen.  
As can be seen from Figure 7, the complexity of hydraulic fractures formed by fracturing in marine shale is significantly greater than that of hydraulic fracturing fractures in continental shale. This is because the brittle minerals in marine shale are predominant, which contribute to the expansion of fractures and the generation of complex fracture networks during the fracturing process, while the clay minerals in continental shale are predominant, which are more likely to form a single fracture.  
The S-2 fracture morphology of marine shale shows that under low-displacement fracturing, after hydraulic fractures start from the bottom of the well, they are captured by the laminar facies near the wellbore, and the hydraulic fractures are unable to traverse the laminar facies, with a single fracture morphology. S-3 shows that the fracture morphology of marine shale is more complex after the use of hydrochemicals. The S-4 fracture morphology shows that under the case of a large stress difference, the specimen is prone to form a single longitudinal main fracture through the laminar facies.  
The natural laminar joints of continental shale are extremely developed, and the hydraulic fractures are easily captured by the laminae. Y-2 and Y-3 show that, with the use of small-displacement fracturing and fracturing after hydration, a large amount of fracturing fluid percolates into the laminar joints, and the hydraulic fractures are dominated by laminar joints. From the fracture morphology on the surface of the specimens after fracturing in S-1 and S-4, it can be seen that the stress difference has a significant effect on  
Figure 7: Shale fracture morphology under different fracturing condition. S represents marine shale; Y represents continental shale. Red solid lines indicate hydraulic fractures; blue solid lines indicate natural fractures; black solid lines indicate laminated fractures.  
the extension morphology of hydraulic fractures in continental shale; under the condition of stress difference of 5 MPa, the hydraulic fracture is unable to traverse the laminar joints and is captured by laminae at the near wellbore, and the fracture morphology is relatively homogeneous. When the stress difference increases to 10 MPa, the hydraulic fracture turns when it extends vertically to the weak surface of the laminae, and then extends along the laminae through the specimen, with a higher fracture complexity.