# Profile Control Using Fly Ash Three-Phase Foam Assisted by Microspheres with an Adhesive Coating
## 3 Results and Discussion
### Oil-Displacement Efficiency  
As depicted in Figures 8 and 9, the oil recovery of parallel cores is improved to a certain extent after foam injection in all the performed experiments, demonstrating effective profile control by the three-phase foam.  
Figure 8: The influence of the three-phase foam slug size on oil displacement in parallel cores of permeability ratio 5: (**a**) 0.2 PV; (**b**) 0.3 PV.  
Figure 7: Influence of permeability ratio on fractional flow rates: (**a**) permeability ratio 5520/29; (**b**) permeability ratio 10,200/30.  
During the primary water flooding, the injection pressure exhibits a slight decline, while the water cut surges. The decrease of the injection pressure and the increase of the water cut arise from the presence of a water breakthrough channel that reduces flow resistance. The oil recoveries after primary water injection into parallel cores of permeability ratio 5 are 29% and 20%, respectively. The difference might be ascribed to the variance of core heterogeneity, which causes different injection periods of the primary water floods. We cease the primary water flooding when the water cut reaches 98%. In comparison, the primary water flooding in parallel cores of permeability ratio 10 yields an oil recovery of 22% for both tests. The lower oil recovery originates from the higher permeability ratio that delivers a larger difference in the fractional flow rate, thereby less oil production in the low-permeability cores.  
The notable increase of injection pressure during foam injection arises from the significant foam resistance. As continuously pumped into the parallel cores, the MCL assisted three-phase foam selectively enters the high-permeability zone, plugs the pore throats inside the water breakthrough channel, and thus significantly reduces water cut and expands the swept volume. Due to the growth in flow resistance, the difference between the fractional flow rates of the high- and low-permeability cores narrows down during the injection of the subsequent water. Thus, more oil is recovered from the low-permeable layer. The injection pressure presents a further remarkable growth in the early period of subsequent water injection, manifesting that the three-phase foam remains effective in pore plugging. It is worth mentioning that the injection pressure during the subsequent water flood declines to a level that is a bit higher than the initial injection pressure, which might be caused by the migration of MCL and its ability in profile control.  
The enhanced oil recoveries in parallel cores of permeability ratio 5 are about 25% and 30% for 0.2 PV and 0.3 PV foam injection, respectively. In comparison, the enhanced oil recoveries in parallel cores of permeability ratio 10 are about 30% and 36% for 0.2 PV and 0.3 PV foam injection, respectively. As expected, the injection of 0.3 PV foam results in a higher EOR in parallel cores of various permeability ratios due to its better performance in pore blocking. This complies with the fact that 0.2 PV foam injection yields a lower breakthrough pressure than that of 0.3 PV foam injection. Furthermore, a higher permeability ratio leads to higher EOR, which substantiates the effectiveness of the three-phase foam system in sealing high-permeability channels. This conclusion is contradictory to the result presented in Section 3.4.3, where we conclude that a larger permeability ratio gives rise to worse profile control. The contradiction might originate from the wide difference in the permeability ratios of those cores used in our experiments. When the permeability ratio is small, a larger permeability ratio can lead to a more effective  
Figure 9: The influence of the three-phase foam slug size on oil displacement in parallel cores of permeability ratio 10: (**a**) 0.2 PV; (**b**) 0.3 PV.  
redistribution of the fractional flow. Nevertheless, when the permeability ratio is overlarge, the effectiveness of profile control is indistinctive and less fraction of fluid diverts to the low-permeability channels.