**2.1 Main applied technology of shale reservoir fracturing**

Fracturing technology of shale reservoirs can be classified based on the type of well fracturing into three categories, vertical, deviated, and horizontal fracturing wells, as shown in **Figure 1**. Fracturing technology can also be divided based on the type of fracturing fluid used such as gas, foam, gel, etc. Target zone can be fractured into different sections as single section and multi-section fracturing. Moreover, various factors should be taken into account while choosing the choice of fracturing fluid and fracturing technology such as the shale gas reservoir depth, capacity and formation sensitivity, natural fractures, and the well completion technology [6].

The most commonly used fracture technologies now are the multi-section fracturing, riverfracing, hydra-jet fracturing, fracture network fracturing, re-fracturing, and simultaneous fracturing. However, more attention is being given to CO2 and N2 fracturing. This fracturing technology's features and application conditions are different as shown in **Table 2**.
