## 3 Experimental Results  
### Hydraulic Fracturing  
After the experiment, the red tracer was injected into the wellbore to observe the seepage locations of the tracer on the surface of the rock sample, thereby assessing the fracture morphology. The top surface and four side surfaces of the cubic rock sample are displayed according to the placement shown in Figure 4, and the same is true for the deflagration fracturing. When necessary, a 150\(\times\) microscope was used to observe the microscopic morphology of the fractures in the fine details of the rock samples. The four experiments terminated with the observation of water flowing out of the equipment, and the final failure modes of the four specimens are illustrated in Figure 5. Two primary types of specimen failure were observed: cracks and localized damage zones. The cracks represented continuous, interconnected damage with a certain width, and in the case of hydraulic fracturing, the crack widths generally ranged in the order of tens of micrometers (Figure 6a). The localized damage zones, on the other hand, exhibited non-interconnected, cluster-distributed characteristics, which is demonstrated well by the tracer seepage patterns within the damage zones in Figure 6b,c. For specimens containing a single borehole (Figure 5a-c), the induced damage primarily radiated outward from the borehole center. The damage was predominantly distributed along a \"left-top to right-bottom\" direction (from a top-view perspective, that is to say, X--Y+ to X+Y--), and based on the damage locations on the X-- and X+ surfaces, it can be inferred that the internal damage essentially penetrated the entire specimen. Under heated conditions, more localized damage zones were observed in the specimens, while only cracks were exposed on the surface of the specimen (a) loaded at room temperature. In the case of the specimen with dual boreholes, the damage was primarily concentrated in the X--Y+ portion of the specimen, and there was no clear evidence indicating that the internal damage had fully penetrated the specimen. Figure 7 presents the curves of the fluid pressure within the wellbore, the injection rate, and the sample temperatures with time in each experiment. During the injection process, the injection rate was initially set at 15 mL/min and then increased gradually. In Figure 7c,d, the injection rate is shown as 0 due to the limited capacity of the plunger pump, which necessitated refilling the pump with water after depletion. During this time, the valve between the pump and the wellbore was closed to maintain the pressure within the wellbore as consistently as possible. Figure 4: A demonstration of the surface damage of rock samples. Figure 5: The damage distribution diagram of the sample after hydraulic fracturing, (**a–d**) correspond successively to the four cases H1–H4. The red lines in the figure represent exposed cracks, and the red circles indicate localized damage zones. Figure 6: Observation of specimen failure. (**a**) Hydraulic fracturing cracks observed under a portable microscope; (**b**, **c**) damage zone revealed by tracer-based seepage visualization. The comparison reveals that under room temperature conditions, a sudden drop happened for the fluid pressure during the initial stage of the fracturing process ((a)-(i) and (d)-(i) in Figure 7), followed by a gradual stabilization. This indicates that once localized brittle fracture occurred within the rock mass, the fluid diffused along the newly formed cracks, leading to continuous crack propagation. In contrast, for the injections under high-temperature conditions depicted in Figure 7b,c, after the fluid pressure reached its maximum, a more gradual stress drop was observed. Moreover, as the injection rate increased, the rate of pressure decline became more pronounced. Due to the limited monitoring means employed in this experimental study, the internal damage evolution within the sample during the fracturing process remains unknown.