## 3 Experimental Methodology
### Fracturing Test Procedure  
The oven-dried samples were removed from the oven and allowed to cool for 6 h. A newly-modified high-pressure triaxial setup (Figure 2) was used to carry out the fracturing tests. The bottom pedestal of the triaxial setup was modified for the fracturing test by introducing two O rings into the pedestal. As shown in Figure 3a, the two O rings seal the fluid injection hole at the centre of the pedestal. After placing the sample (Figure 3c), the wellbore and the fluid injection hole were aligned and with the two O rings fluid only entered the wellbore. Since there was a possibility for the fluid to be pressurised at the bottom of the sample, the fluid contact area was minimised using a small O ring. In this study, water was used as the fracturing fluid and injected at a constant flow rate of 5 mL/min using a syringe pump. This flow rate was selected based on the fluid leak-off during the fracturing test, where, flow rates below 5 mL/min were unable to achieve the breakdown pressure with limited pump volume, due to fluid leak-off and the pressurization of the rubber membrane of the sample. However, higher flow rates (5 mL/min) may cause unstable fracture growth during the fracture initiation; this can be avoided by using a flow restriction device (check) in the injection line just before the sample. In this study, there is a needle valve (which is slightly opened during the fracturing test) in the injection line, close to the sample, and the injection pressure transducer is located in between the sample and the needle valve. This needle valve was used to control the flow to the sample and pressure transducer after that was used to measure the fluid pressure on the sample, while inbuilt pressure transducer in the syringe pump was used to observe the pump pressure during the experiments. It should be noted that, before starting the water injection, the pipeline was filled with water to remove all the gas bubbles. Fluid injection was then performed until the breakdown pressure of the sample was reached and the process was repeated for four confining pressures: 1, 3, 5 and 7 MPa. In relation to field conditions, 7 MPa confining pressure represents a depth of about 300 m, which is less than the depth of the shale reserves (about 5 km). However, in order to represent 4 km depth in laboratory conditions, the required confining pressure is about 125 MPa, which is far more than the capacity of the test rigs available. Furthermore, in order to fracture the rock specimens at 125 MPa confining pressure, it would require an injection pressure of about 250 MPa, which is also not possible in laboratory conditions. Therefore, low confining pressures were selected for this study considering the experimental facilities available. For all the samples, applied axial stress was maintained at 20 MPa constant value, which is greater than the confining pressure required to obtain a longitudinal fracture along the wellbore. It should be noted that the selected flow rate of 5 mL/min is significantly lower than that in actual field conditions (which is about 0.2 m/s) and fluid viscosity remained almost the same for both experimental and field conditions. This will affect the fracturing time and characteristics, and therefore, the scaling laws should be considered. According to [PERSON] et al. (2018), due to the scaling effect, when the time is short, fractures are characterized by large viscous dissipation and small leak-off, while when the time is significant, fractures are characterized by small viscous dissipation and large leak-off. According to [PERSON] (2019), in field conditions, fracture development can be toughness-dominated or viscous-dominated. However, during the initiation phase, fracture development is toughness-dominated. Interestingly in radial fractures, initially the fracture development is toughness-dominated and then it becomes viscous-dominated and again at the final stage, it becomes toughness-dominated (2019).