Abstract
Polymer flooding is an enhanced oil recovery (EOR) technique that aims to enhance the stability of the flood front in order to increase sweep efficiency and thereby increase hydrocarbon recovery. Polymer flooding studies often focus on large-scale sweep efficiency and neglect the impact of the pore-scale displacement efficiency of the multi-phase flow. This work explores the pore-scale behavior of water vs polymer flooding, and examines the impact of rock surface wettability on the microscopic displacement efficiency using digital rock physics. In this study, a micro-CT image of a sandstone rock sample was numerically simulated for both water and polymer flooding under oil-wet and water-wet conditions. All simulations were performed at a capillary number of 1E-5, corresponding to a capillary dominated flow regime. Results of the four two-phase flow imbibition simulations are analyzed with respect to displacement character, water phase break-through, viscous/capillary fingering, and trapped oil. In the water-wet scenario, differences between water flood and polymer flood are small, with the flood front giving a piston-like displacement and breakthrough occurring at about 0.4 pore volume (PV) for both types of injected fluid. On the other hand, for the oil-wet scenario, water flood and polymer flood show significant differences. In the water flood, fingering occurs and much of the oil is bypassed early on, whereas the polymer flood displaces more oil and thereby provides better microscopic sweep efficiency throughout the flood and especially around breakthrough. Overall the results for this rock sample indicate that water flood and polymer flood provide similar recovery for a water-wet condition, while the reduced mobility ratio of polymer flood gives significantly improved recovery for an oil-wet condition by avoiding the onset of microscopic (pore-scale) fingering that occurs in the water flood. This study suggests that depending on the rock-fluid conditions, the use of polymer can impact microscopic sweep efficiency, in addition to the well-known effect on macroscopic sweep behavior
Highlights
For most oil reservoirs, a large amount of oil is left behind in the formation trapped within the rock, even after extensive water flooding
As early as the 1960s, polymer flooding has been suggested as an enhanced oil recovery (EOR) method that could improve the oil displacement process by increasing the viscosity of the displacing fluid (Pinto et al, 2018)
As seen in the production curves, the residual oil saturation is lower for polymer flooding than water flooding, and by a larger amount under oil-wet condition
Summary
A large amount of oil is left behind in the formation trapped within the rock, even after extensive water flooding. A contributing factor to poor sweep efficiency of a water flood can be fingering of the injected fluid into preferred paths, resulting in a lot of bypassed oil. As early as the 1960s, polymer flooding has been suggested as an enhanced oil recovery (EOR) method that could improve the oil displacement process by increasing the viscosity of the displacing fluid (Pinto et al, 2018). Low concentrations of water soluble and high molecular weight polymer are added to the injected water to reduce the mobility of the displacing phase and thereby decrease the tendency for viscous fingering. The mobility ratio (M) compares the mobility of displacing and displaced fluid phases in porous media, and a high mobility ratio can lead to the fingering phenomena resulting in an undesirable loss of sweep efficiency (Velandia, 2013)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
