**3.2 Foam fracturing fluid**

 Foams have been found to be the most promising and appropriate fluid to fracture shales and improve the recovery efficiency. Although the cost of operation increases, the benefits are much higher than the incremental cost [35]. The structure of foams has the ability to provide an increased effective viscosity without plugging reservoir pores and causing formation damage by forming any filter cake [28]. It has an increased efficiency due to reduced fluid loss coefficients, high viscosity inside induced fractures and negligible sand settling velocities [28, 36]. Foam application also gives an increased capability of proppant distribution and proppant placement over the entire fracture length. Due to high foam apparent viscosity, it is achievable to have an improved proppant suspension and placement. In foam fracturing, the utilization of gas as a replacement to a significant amount of the liquid phase assists hydrocarbon recovery by decreasing formation damage and water blocking. Foam utilization eliminates the need of any additional additives such as cross linkers, gel breakers, etc. It also decreases the amount of produced water and its treatment cost. Moreover, the expansion of gas assists liquid flow back and helps fracture cleanup.

Foams are typically generated by a surfactant solution (base fluid), in some cases, in combination with a small amount of polymer as a stabilizer and other additives. Surfactants that are used as a foaming agent may help to lower the surface

**Figure 5.**  *Proppant conditions after performing fracturing job using different types of fracturing fluids [34].* 

*CO2 Foam as an Improved Fracturing Fluid System for Unconventional Reservoir DOI: http://dx.doi.org/10.5772/intechopen.84564* 

tension of the fracturing fluid and avoids water blocking by recovering fracturing fluid after the job completion [37]. Both laboratory and field scale tests have shown that the addition of surfactant increases the gas production by reducing the capillary forces and altering the wettability of shales. The rheology of foam has great importance in fracture treatment design and has been discussed by multitude of studies [8, 36, 38–40].
