# Fracturing Fluids and Their Application in the Republic of Croatia
## 5 Fracturing Fluids--Composition and Additives
### Classification of Fracturing Fluids
#### 5.1.6 Energized Fracturing Fluids  
Energized fracturing fluids include liquefied CO\({}_{2}\), N\({}_{2}\), He and natural gas (see Table 10).  
The use of N\({}_{2}\) and CO\({}_{2}\) overcomes and mitigates many of the challenges associated with traditional water-based hydraulic fracturing fluids by reducing the high volumes of water, chemicals and even proppant, and increasing oil and gas production from tight or water sensitive formations as well as unconventional reservoirs such as shale, tight sands and coalbed methane. CO\({}_{2}\) fracturing has achieved great success in North America (first used in the 1980s), and began to be applied in China [56]. It has been widely used in reservoirs with a permeability from 0.1 to 10,000 \(\times\) 10\({}^{-3}\)\(\upmu\)m\({}^{2}\), with the deepest treated depth  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Base Fluid** & **Fluid Type** & **Composition** & **Used for** \\ \hline  & liquefied carbon dioxide & CO\({}_{2}\) & \\ \hline liquefied nitrogen & N\({}_{2}\) & low permeability reservoirs, \\ \hline liquefied helium & He & water-sensitive formations, low \\ \hline liquefied natural gas & LNG (butane and/or & formation pressure \\  & & propane) & \\ \hline \hline \end{tabular} \
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{Advantages} \\ \hline \hline \end{tabular}
\begin{tabular}{c} There are potential environmental advantages: water usage is very reduced or completely eliminated, few or no chemical additives are required, and some level of CO\({}_{2}\) sequestration is achieved. There is a reduction in formation damage (reduction in permeability and capillary pressure damage by reverting to a gaseous phase; no swelling induced) [27]. They form more complex micro-fractures, which can connect many more natural fractures greatly, increasing maximally the fracture conductivity [55]. They enhance gas recovery by displacing the methane adsorbed in the shale formations [55]. The evaluation of a fracture zone is almost immediate because of rapid cleanup. The energy provided by CO\({}_{2}\) results in the elimination of all residual liquid left in the formation from the fracturing fluid. There is a better cleanup of the residual fluid, so a smaller mesh program can be used and supplies adequate fracture conductivity in low permeability formations. The use of a low viscosity fluid results in more controlled proppant placement and higher proppant placement within the created fracture width.  
Disadvantages  
The main disadvantages arise from the fluid’s low viscosity. The proppant concentration must be lower and proppant sizes smaller, which decrease fracture conductivity. CO\({}_{2}\) must be transported and stored under pressure (typically 2 MPa) and temperature (\(-\)30 \({}^{\circ}\)C). Another disadvantage is the corrosive nature of CO\({}_{2}\) in the presence of H\({}_{2}\)O. There are unclear (potentially high) treatment costs.  
\end{table}
Table 10: Energized fracturing fluids.  
of over 3000 m and a bottom temperature from 10 to 100 \({}^{\circ}\)C [56]. In CO\({}_{2}\) fracturing, 100% liquid CO\({}_{2}\) is used as a fracturing agent and therefore represents a promising alternative to hydraulic fracturing since it can avoid problems arising with the use of water [57]. Fractures generated in liquid CO\({}_{2}\) fracturing are narrower than those in hydraulic fracturing because of the very low viscosity of CO\({}_{2}\), so it is currently only suitable for low permeable gas reservoirs [56]. The viscosities of liquid CO\({}_{2}\) and supercritical CO\({}_{2}\) are approximately 10% and 2% of the viscosity of pure water, respectively, so their penetration into rock matrix pores is much faster than that of water. The injection of CO\({}_{2}\) results in lower breakdown pressures and more complex and well-connected fracture networks than the injection of water [57].