## 3 Hydraulic Fracturing Experiment
### Experimental Results
#### 3.5.2 Laminar Dip Angle  
Using the hydraulic fracturing physical simulation experiment system, based on previous experiments, we set the shaft pressure at 3 MPa, the surrounding pressure at 25 MPa, and the injection rate at 0.02 mL/s and conducted hydraulic fracturing physical simulation experiments on shale rock samples with lamina angles of 30\({}^{\circ}\) and 60\({}^{\circ}\) to analyze the relationship between the lamina face angle and hydraulic fracture formation and expansion. The experimental design and specific parameters are shown in Table 5.  
The W-19 rock sample was drilled at an angle of 30\({}^{\circ}\) to the parallel laminae direction, and a laminae seam with an approximately 30\({}^{\circ}\) angle to the borehole axis was visible near the buried pipe end before the experiment, in addition to a fracture along roughly the borehole axis and intersecting the laminae seam. After the experiment, the laminated seam intersected the borehole obliquely, the initial axially oriented fracture connected to it was opened, and a newly formed hydraulic fracture was present on the symmetrical side of the core. The photograph of the specimen W-19 after the test and the pumping pressure curve are shown in Figure 26. Eventually, a mixed-type seam network with hydraulic seams, laminar seams, and primary fractures opened simultaneously. From the pump pressure curve, the pump pressure first showed a linear increasing trend with time, and then the slope of the pump pressure increase slowly decreased, indicating the formation of new fractures in the core, and no obvious drop was observed in the pump pressure curve, which was mainly due to the influence of the primary fractures. The seam opening was larger, the high-pressure fluid inside the triaxial chamber after the fracture opening rapidly entered the interior of the core, and the pressure between the wellbore and the triaxial chamber was basically balanced, resulting in no steep drop in pressure. The pressure between the wellbore and the triaxial chamber was basically balanced, resulting in no steep pressure drop. The rupture pressure is 28.82 MPa, which is only 3.82 MPa higher than the surrounding pressure, and the rupture pressure of the rock is greatly reduced due to the influence of the weak structural surface. In addition, it can be observed that when a certain angle exists between the coring direction and the laminae, the fracture along the axial direction of the borehole will roughly deflect to the laminae direction to a certain extent, and when the fracture deflects and expands to a certain length, the fracture will return to the direction of the borehole axis and continue to expand again. The W-20 rock sample was drilled at an angle of 60\({}^{\circ}\) to the laminae, and there were no obvious cracks or defects on the surface of the rock sample before the experiment. After the experiment, hydraulic fractures were formed on the two symmetrical flanks, and obvious fracture deflection could be observed on the fractures on both flanks. The photograph of the specimen W-20 after the test and the pumping pressure curve are shown in Figure 27. The deflection angle was approximately equal to the angle between the laminae and the borehole axis at the deflection point, and the deflection angle gradually decreased with the expansion of the fractures and, finally, was roughly parallel to the borehole axis. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Specimen** & **Fracturing** & **Laminar** & **Displacement** & **Shaft** & **Surrounding** & **Rupture** \\
**Number** & **Fluids** & **Perspective** & **(mL/s)** & **Pressure** & **(MPa)** & **(MPa)** & **Pressure** \\ \hline W–19 & Slippery water & 30 & 0.02 & 3 & 25 & 28.82 \\ W–20 & Slippery water & 60 & 0.02 & 3 & 25 & 44.28 \\ W–11 & Slippery water & 90 & 0.02 & 3 & 25 & 51.36 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Experimental results of hydraulic fracturing under different lamina angle conditions.