Analysis of Low Salinity and Polymer Synergies in a Dynamic Pore-Scale Network Simulator

It has been postulated that combining different EOR techniques might yield a synergistic behaviour that could result in additional oil recovery beyond that obtained from each EOR technique applied separately. This has been investigated in recent experimental work (Alagic et al., 2010; Mohammadi and Jerauld, 2012 ; Shiran and Skauge, 2013 ; Pettersen and Skauge, 2016), where both polymer and surfactant solutions have been reported to be more efficient in a low salinity environment. We have investigated a number of different injection protocols using a pore-scale dynamic simulator that combines both low salinity brine (LS) and polymer injection.

Four synergistic combinations have been considered: (i) LS brine and polymer injected simultaneously at the start of the simulation (secondary mode), (ii) LS brine and polymer injected simultaneously following high salinity (HS) water breakthrough, (iii) LS brine injected initially, followed by simultaneous LS brine/polymer injection after LS breakthrough, and (iv) LS brine injected initially followed by polymer injection after LS water breakthrough.

A positive synergy was observed when LS brine and polymer were injected simultaneously in both secondary and tertiary modes, with the combined effect yielding significant increases in oil recovery. The mixture of polymer and LS brine was found to cause capillary fingers to thicken and swell, allowing the LS brine to access more of the pore space as a consequence of the higher viscous forces induced by the polymer. In secondary mode, the mixture of polymer and LS brine was observed to stabilise the water fingers and shifted the flow regime from viscous/capillary fingering to stable displacement. Moreover, results suggest that this synergistic LS/polymer effect is sensitive to a range of rock/fluid parameters, such as wettability, viscosity ratio, and capillary number.