*3.1.3 Proppant placement*

The slickwater/water-based fluid fracturing process generally creates longer and skinny fractures. However, a poor delivery of proppant has been reported along much of the fracture and much of the fractures remain un-propped allowing it to close after the pressure is released and fracturing job is over, particularly in ductile rock formation [32]. In addition, the near wellbore region, in this process, is dominantly propped due to rapid sand settling. Gels are used to avoid this rapid settling of proppants; however, the adverse effect which is damaging the proppant pack and the fracture surface can occur. In previous studies, it was suggested to replace sands with ultra-lightweight proppants in order to achieve efficient transport of proppant. Foam fracturing treatment reportedly gives an efficient transport of proppant as compared to the slickwater fluid treatment. Therefore, use of foams can be considered to effectively improve the performance of proppant placement. In foam fracturing, water exposure is avoided alienating the reservoir matrix from the softening effect and hence proppant embedment could be reduced [30].

**Figure 4.**  *Water blocking due to high capillary pressure.* 

Moreover, the interaction between bubbles of gas at high foam qualities gives a large energy dissipation which results in good effective viscosity hence providing more effective proppant placement. Whereas at low foam qualities, the interaction among gas bubble is minimum and the fluid viscosity behavior is similar to that of base fluid. **Figure 5** shows the condition of proppant pack formed using three different fracturing fluid systems [33]. It is clear that energized fluid or CO2 foam provides efficient proppant placement, whereas the water and gel-based proppant have poor permeability due to proppant embedment and gel residue, respectively [33].
