# A Computational Study of Polymer Solutions Flow Regimes during Oil Recovery from a Fractured Model
## 3 Results and Discussion
### Influence of Polymer Concentration on Oil-Displacement Process
This is shown in Figure 9. It can be seen that, with the increasing polymer concentration, the velocity field becomes more uniform. In addition to increasing the viscosity of the solution, increasing the velocity near the channel walls also improves oil recovery. To quantify the oil-displacement process from a fractured medium, in the course of conducted calculations, the dependence of the oil-recovery factor on the displacement time was obtained. This dependence is shown in Figure 10a for water and two concentrations of polymer. Subsequently, the oil-recovery factor (ORF), obtained from the calculation results of displacement, was constructed depending on the polymer concentration (see Figure 10b); zero concentration on the graph corresponds to water. Figure 10b shows the steady-state ORF values at time 6s, the color of the symbols corresponds to the lines in Figure 10a. As can be seen from the graphs shown in Figure 10a,b, using polymer solutions enhances the oil-recovery factor from a fractured medium from 0.45 (when displaced by water) to 0.74 when displaced by a polymer solution with a weight concentration of 0.05%. A further increase in the concentration to 0.1% leads to enhancing the oil-recovery factor to 0.85. Such a significant enhancement of the ORF is due to the fact that the viscosity of polymer solutions increases significantly compared to that of water, and also that these solutions are non-Newtonian fluids (whose viscosity coefficient depends on the shear rate). The displacement front for polymer solutions is wider in comparison with that for water. When displaced by water, the viscosity of water is lower than the oil viscosity, while for polymer solutions, the effective viscosity at low shear rates turns out to be comparable to the oil viscosity. Changing the viscosity of the displacing agent leads to an increase in the pressure drop during the oil displacement from the fractured medium. In the course of calculations, we obtained the dependences of the pressure drop in a fractured medium when displaced by water or polymer solutions with different concentrations. Figure 11a shows the time dependence of the pressure drop in a fractured medium during displacement by various displacing agents. To simplify the comparison of the pressure drops when using water or polymer solutions of different concentrations, the dependence of the averaged pressure  
Figure 9: Velocity fields during the flow of water and polymer solutions with different concentrations. drop at the steady-state section was constructed when the oil-recovery factor values did not change. The dependence of the steady-state pressure drop on the weight concentration of the polymer is shown in Figure 11b, the color of the symbols corresponds to the lines in Figure 11a. As can be seen from the graphs presented, using polymer solutions significantly increases the pressure drop used on injection in the steady-state area. Thus, for a polyacrylamide solution with a concentration of 0.05%, the pressure drop increases by seven times compared to that for water. With an increase in concentration to 0.1%, the pressure drop increases by 10.8 times relative to that when displaced by water. The analysis of the breakthrough time of the displacement agent through a fractured medium filled with oil was carried out during the calculations. Figure 12 shows the breakthrough time of the displacing agent depending on the weight concentration of polyacrylamide. With an increase in the polymer concentration, the breakthrough time  
Figure 11: Pressure drop vs. time (**a**), and the averaged pressure drop at steady flow mode vs. polymer concentration (**b**). Figure 10: Oil-recovery factor vs. time (**a**), and the overall oil-recovery factor vs. concentration of the polymer solution (**b**). increases.