Abstract This study focuses on the investigation of the total pressure drop with regards to the shear, elongational and frictional forces experienced by the viscoelastic EOR polymers during the flow through porous media. The main analysis is performed to these forces occurring at low Reynolds numbers. Single-phase flooding experiments were conducted in Bentheimer core plugs and micromodels. Moreover, observations at pore-scale level are included by streamlines visualization analysis. The overall approach can be summarized in the following sequence: 1) Single phase polymer flooding through Bentheimer core plugs 2) Analysis regarding the correlation between the pressure drop and the apparent flow behavior. This analysis also focuses on the contribution of shear, elongational and frictional forces to the pressure drop at low Reynolds number 3) Porescale streamline visualization experiments using micromodels 4) Analysis regarding the elastic instabilities or turbulences observed during the flow at low Reynolds number from streamline visualization experiments. The preliminary evaluation from core flooding experiments shows a significant additional increase in pressure drop during the viscoelastic EOR polymers flow through porous media. The analysis regarding the cause of the additional increase in pressure drop indicates that shear and frictional forces are not the main determinants during the flooding process. This leads to a strong indication that the elongational forces experienced by the EOR polymers while flowing through the pores are the primary reason for the additional increase in pressure drop. A correlation between elongational forces and flow instabilities during the experiments was observed. It was also observed that at a given shear rate the onset of elasticity occurs. The onset of elasticity was evaluated by the observation of the normalized data obtained by taking the ratios between apparent and bulk viscosity. Further evaluations from the porescale streamlines visualization experiments showed a clear occurrence of elastic instabilities during the flow at low Reynolds numbers in the form of vortices, crossing streamlines, and steadily changing flow directions of streamlines. These flow instabilities account for the additional increase in pressure drop. This study provides a novel comprehensive evaluation approach to characterize the pressure drop observed during the EOR polymers flow through porous media with regards to their viscoelastic behavior. It should help to understand porescale polymer displacement and the contribution of viscoelastic properties on additional oil recovery. Furthermore, this paper provides evidence of the flow instabilities through visualization experiments and detailed analysis.

Aqueous polymers used in enhanced oil recovery (EOR) applications exhibit Newtonian and Non-Newtonian behavior depending on the interstitial velocity or the stress magnitude that is submitted during the flooding process. This behavior will cause different pressure changes while flowing through the porous media. A new correlation proposed by the authors is utilized as an input to COMSOL Multiphysics® software. The correlation describes the polymer flow by examining the pressure drop associated with the flow dominated by extension and differentiate them of those dominated by shear. Commercial reservoir simulators are able to simulate the total pressure drop measured from the laboratory experiment by only assuming shear thickening behavior throughout the flooding experiment. Meanwhile, the total pressure drop from the flooding experiment itself actually results from both the shear thinning behavior and the shear thickening behavior. In other words, the simulators cannot separate the pressure drop contribution from shear (shear thinning) and elongation (shear thickening) deformation of the polymer molecules, which will take place due to the contraction and expansion in the pore geometry. Therefore, the main objective of this paper is to implement the proposed correlation in COMSOL Multiphysics to take into account the contribution of shear and elongation deformation to the total pressure drop observed during the experiment. The Darcy Law interface was used to calculate the pressure difference in single phase condition. 3-D core model (Figure 1) was constructed in COMSOL® and the flow direction is assumed to be only in the x-direction. The free tetrahedral mesh (Figure 2) was selected as the mesh type of the simulation model with the element size of extra coarse to reduce simulation time. The mesh was calibrated for fluid dynamics. In the laboratory experiment, the core sample was surrounded by the confining pressure to create the linear flow direction, while no flow boundary was selected in the simulator to replace the confining pressure. The proposed correlation was utilized as variables in COMSOL. Due to Multiphysics capabilities of COMSOL, we can implement the new correlation to separate shear and elongation contribution to the pressure drop during aqueous polymers flow in the porous media (Figure 3). As a result, we can reproduce the total pressure drop from the experiment, particularly in the high rate region (shear thickening) by using the simulator. Moreover, the implementation of the proposed correlation leads us to the new insight of the displacement efficiency by polymer enhanced oil recovery (EOR) method.

This paper investigates the nonNewtonian behavior of aqueous polymers solutions while flowing through porous media with the support of COMSOL Multiphysics. The single phase Darcy Law interface was used to solve Darcy’s equation in order to calculate the pressure drop that occurred during the core flooding experiment. Furthermore, an equation proposed by some of the authors was utilized as an input to the simulator. The results are validated by quantitatively comparing the results from the simulation with those obtained from the laboratory experiment. Results obtained from the simulation showed to be in good agreement with the experimental results, indicating a successful implementation of the proposed equation in the simulator. Due to its capabilities and flexib le framework to integrate physical and chemical mechanisms during polymer flow in the porous media or enhanced oil recovery (EOR) processes, COMSOL provides an alternative for current reservoir simulators used in the oil and gas industries.