Experimental Evaluation of Polymer Viscoelasticity During Flow in Porous Media: Elongational and Shear Analysis

Abstract

Abstract 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.