# A Computational Study of Polymer Solutions Flow Regimes during Oil Recovery from a Fractured Model
## 3 Results and Discussion
### Investigation Influence of the Oil Viscosity  
The effect of oil viscosity on the oil-recovery factor (ORF) and pressure drop has been studied when using various displacing agents. Calculations were carried out for water and a polyacrylamide polymer solution with a molecular weight of \(\sim\)9 mln c.u. at a weight concentration of 0.1%. Rheological parameters, wetting angle, and surface-tension coefficient for this polymer solution were determined experimentally. Calculations were performed for the capillary number of 4 \(\times\) 10\({}^{-5}\). In the calculations, the oil density was equal to 900 kg/m\({}^{3}\) and the oil-viscosity values were equal to 0.0157 and 0.1 Pa\(\times\)s, which, respectively, corresponded to high-viscosity oil and extra viscous oil.  
A comparison of oil-displacement patterns using water and 0.1% polyacrylamide solution from the fractured medium model is shown in Figure 15. Blue color shows the pore space filled with oil, red is the displacing agent, and white color corresponds to solid rock. It can be seen that, for both considered oil viscosities, in contrast to displacement by water, the displacement using a polymer solution occurs through a wide displacement front covering the entire computational domain, whereas, after displacement by water, especially for high-viscosity oil, many existing zones of pore space filled with oil are not involved in the displacement process.  
Quantitative estimation of the calculation results can be done by graphs representing the ORF depending on the weight concentration of the polymer for two values of oil viscosity (see Figure 16a). As can be seen from the graph shown in Figure 16a, the largest increment of the oil-recovery factor, when using a polymer solution, is observed for oil with a higher viscosity (0.1 Pa\(\times\)s), compared to that for using water. The recovery factor of high-viscosity oil by water was 0.468 while using a polymer solution allowed obtaining ORF equal to 0.88. For oil with a lower viscosity (0.0157 Pa\(\times\)s), the increment of the ORF when using polyacrylamide solution is less significant compared to that for using water; the oil-recovery factor is 0.784. Using a polymer solution for oil displacement allows obtaining an ORF equal to 0.98. The difference in the increment of the ORF is due to the fact that high-viscosity oil is well-enough displaced by water.  
In the course of calculations, the dependences on the pressure drop during oil displacement with water and polymer solutions having different viscosities were obtained (Figure 16b). The pressure drop was determined at a steady section of the displacement process providing a constant value of the ORF. During oil displacement, the pressure drop increases due to both an increase in oil viscosity and the high viscosity of the polymer solution. When displaced by water, an increase in the oil viscosity leads to an increase in the pressure drop by 2.13 times. For an oil viscosity equal to 0.0157 Pa\(\times\)s, when displaced by a polymer solution, the pressure drop is 17.7 times higher than that for water. With an increase in the oil viscosity, the difference in the pressure drop between the polymer solution and water decreases. Thus, at an oil viscosity of 0.1 Pa\(\times\)s, the pressure drop for a polymer solution is 11 times higher than that for water.  
Figure 15: Phase distribution of the displacing agent and oil in a fractured medium during the displacement process. Effect of viscosity oil.