Title : Rheological and geochemical interactions of low salinity polymer on rock-brine interactions
Abstract:
Recently, there has been growing interest in the synergistic combination of low salinity water with polymer flooding as a technique for enhanced oil recovery. Numerous studies have been conducted to investigate the efficiency of low salinity polymer (LSP) flooding in sandstone oil reservoirs; however, a clear conclusion on the driving mechanism has not yet been reached. Detailed explanations regarding the relative contribution of rock/fluid and fluid/fluid interactions to enhance oil recovery through LSP flooding are lacking. This study aims to investigate the impact of LSP on the rheological and geochemical interactions between equilibrated formation brine samples and Boise rock.
Rheological and ionic analyses were performed to characterize the properties of equilibrated formation brine samples with Boise rock in the absence and presence of polymer under different brine chemistries. The results suggest that salinity has a stronger effect on the viscoelasticity of the HPAM polymer compared to composition. This can be attributed to the fact that changes in brine composition have a lesser impact on the screening of electrostatic interactions between polymer chains compared to changes in salinity. Consequently, the association between the chains weakens, leading to an overall reduction in the viscoelasticity of the polymer.
Additionally, the results reveal that the presence of the polymer decreases ion concentration in the equilibrated brine, which may be attributed to polymer adsorption on the rock surface. This finding aligns with previous results and substantiates the role of the polymer in reducing brine content by forming a protective barrier, limiting ion diffusion through exclusion mechanisms, and forming complexes with divalent cations.
Furthermore, a notable increase in calcium concentration in the equilibrated brine is observed when the calcium and magnesium ions are absent in the polymer solution. This observation supports the concept of ions migrating from rock to brine until concentration equilibrium is achieved, driven by the concentration gradient. The significance of this finding underscores the importance of considering the impact of divalent ions on rock-brine geochemical interactions in the presence of the polymer.
