We present a comprehensive workflow to obtain the best insights into the viscoelastic behavior of polymers. Viscoelasticity is depicted in most cases by the current commercially available polymers used for EOR applications. The phenomenon is debated to be one of the reasons for additional oil recovery during polymer flooding applications. It is somehow accepted that polymer increases volumetric sweep efficiency owing to improved mobility ratio. Recently researches have explained that flooding polymers in porous media with elastic characteristics could recover additional oil, due to the improved microscale oil displacement (pore-scale). This study focuses on the analysis of polymer viscoelasticity based on single-phase core, sand-pack and capillary tube (CT) experiments coupled with their detailed rheological characterization, in order to evaluate polymer behavior in porous media. A combination of hydrolyzed polyacrylamides (HPAM) polymers as well as a bio polymer is presented throughout this evaluation. The evaluation of the data is addressed on the basis of pressure drop across the pores, separating the shear associated pressure by the extensional thickening associated pressure. Apart from that, viscoelastic dependence of the converging-diverging geometry has been experimented. Based on the observed behavior through porous media, HPAM polymers are compared with bio polymers. Moreover, the behavior of solutions with induced mechanical degradation (pre-sheared) is compared with nonsheared solutions. Similarly, concentrations with different polymer solutions are evaluated. The results obtained in this work allow for additional understanding of polymer solutions behavior in flooding applications. Furthermore The results support the definition of optimized workflows to assess their behavior under flow through porous media. Finally this evaluation helps to describe the parameter that defines polymer viscoelastic properties.

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.

This paper evaluates three viscoelastic phenomena in high molecular weight polymers (24-28 M Daltons) used for EOR applications based on core flooding experiments. First, we evaluate the impact of semi-harsh conditions (salinity, hardness, and temperature). Second, we investigate the impact of polymer degradation (pipe flow and sandface flow) on viscoelastic properties during polymer flooding. Finally, we propose a threefold approach for understanding these polymer viscoelastic properties by characterizing elongational, rotational, and oscillatory behavior. For comparison, polymer solutions were prepared in a typical seawater brine (34 g/L and hardness: R+=0.13) and a typical German field reservoir brine (51 g/L and Hardness: R+=0.26). For experimental evaluation, core flooding experiments in conjunction with rheological, oscillatory, and elongational measurements were performed at room temperature (22°C) and a defined reservoir temperature (55°C). Effluents from core flooding experiments were analyzed to evaluate the changes in viscoelastic properties taking place at the sandface of the reservoir. Capillary tube (CT) injection was performed to simulate mechanical degradation occurring in flow lines. These approaches were used to study the influence of mechanical degradation on polymer viscoelasticity. The polymer solution with deionized water displayed stronger viscoelastic properties, while the same polymer with both brines showed notable loss in viscoelastic properties, specifically at the higher temperature and with hard brine. Pressure drop analysis against interstitial velocity confirmed Newtonian, shear thinning, and thickening dominated flow, as already reported by researchers. Comparing core flood pressure drop data with eVROC pressure data allowed us to determine the turbulence-dominated excessive pressure drop in porous media. In addition, mechanical degradation caused by core flood experiments and CT injection revealed a reduction in elastic-dominated flow using various approaches. Finally, polymer solutions under reservoir harsh conditions (divalent ions, high temperature, and more TDS) resulted in a significant reduction in elastic behavior for all measurements. Compared to previous studies which mainly focused on viscous properties, this study provides a microscale understanding of changes in polymer elastic properties while flowing through porous media depending on reservoir semi-harsh conditions. Confirmation of the existence of turbulence dominated excessive pressure drop in porous media will help understand pore-scale mechanisms in reservoir engineering.

No abstract