Impact of Injection Parameters on Mixing Control by Polymer-Enhanced Low-Salinity Waterflooding

In situ mixing by dispersive transport of salt and viscous fingering between the injected low-salinity (LS) brine and high-salinity (HS) formation brine can jeopardize the performance of low-salinity waterflooding (LSWF). In our previous papers, we demonstrated that in situ mixing can be suppressed by polymer-enhanced low-salinity waterflooding (PELS), in which a small amount of a viscosifying agent, such as a polymer, is added to the LS stream. Nevertheless, effective mixing control with PELS depends upon several factors and operational conditions, which have not yet been addressed. Therefore, this research focuses on the investigation of the impact of injection parameters, such as the polymer concentration, salinity difference, and injection rate, on the performance of PELS. In this regard, single-phase mixing experiments were performed using synthetic sandstone cores (sandpacks). The experimental results reveal that adding only 200 ppm of hydrolyzed polyacrylamide polymer (HPAM) lowers the salt dispersivity by up to 84%, depending upon the salinity difference. The results indicate that higher LS injection rates intensify the salt dispersivity and weaken the performance of PELS as a result of the dependency of polymer solution viscosity upon the share rate. The dependency of dispersivity upon the injection rate increases as the salinity difference increases. On the basis of our experimental data, we developed an empirical model to predict the required pore volume of PELS to displace the resident HS brine in the core as a function of the salinity difference and injection rate. A mathematical model based on the advection-dispersion theory is also presented to calculate the required volume of PELS for consecutive brine injection or slug injection. The results of this paper highlight that PELS is an effective method to increase the performance of formation brine displacement during LSWF and tackle the negative impact of salt dispersion on LSWF, particularly at a large scale. These results are also of use in hydrogeology and contaminant remediation.