**8. Conclusions**

Polymer retention in porous media after the post-polymer brine injection was determined by the residual resistance factor, RRF [59, 62–65, 67, 68, 70–74]. RF and RRF are significant parameters because they provide reliable information on the propagation and effectiveness of polymeric systems as mobility control agents through porous media. **Figure 13** displays the average RF and RRF as a function of the volume of fluid injected normalized for porosity and

The RF curves reveal that the SAP system offers a higher end value of effective viscosity, RF (61%), during flow in porous media relative to the baseline. The SAP RF curve also shows a tendency to level off as a function of the volume of fluid injected, which indicates an appropriate propagation of the SAP network through the unconsolidated porous media. Therefore, the SAP network displays a better performance as mobility control agent compared with the

The RRF curves indicate a larger retention of the SAP system along the sand pack with an end RRF value that stabilizes at around 2.8, while the end RRF value induced by the baseline levels off at approximately 1.3. Therefore, the permeability of the unconsolidated sand packs was further reduced by the SAP system, which aids the displacement and mobilization of

**Figure 14** shows cumulative oil recovery as the percentage of the original oil in place (OOIP) recovered, the ratio of the remaining oil saturation to the initial oil saturation (*S*or/*S*oi), and the water to oil ratio (WOR) as a function of the volume of fluid injected for the water-flooding stage, polymer-flooding stage, and post-polymer water-flooding stage. Water flooding as a secondary oil recovery process on average recovers between 20 and 30% of the original oil in

Polymer-flooding and the post-polymer water-flooding steps rendered an overall percentage of cumulative oil recovery of 41% for the baseline system and 51% for the SAP network. Therefore, the SAP system rendered a 10% higher incremental oil recovery relative to the baseline. In field applications of polymer flooding, an incremental oil recovery of 5% is con-

permeability of the baseline and the SAP system sand-pack displacement tests.

heavy oil by further reducing the relative permeability to water [70, 75].

place [76, 77], which agree with our results.

**Figure 13.** RF and RRF versus volume of fluid injected.

sidered successful [44].

baseline system.

110 Polymer Rheology

A stable supramolecular system was formulated based on the self-assembling of xanthan gum, HPAM, and HMPAM driven by electrostatic interactions through divalent cation (i.e., Ca2+) bridges, which reduce the steric hindrance among anionic polymer chains promoting strong and stable intra- and interpolymer associations via hydrophobic interactions and hydrogen bonding. The viscoelastic functionality of the SAP system is enhanced in high ionic strength aqueous solutions. This performance makes the SAP system suitable for EOR applications involving brines containing high salinity and hardness concentrations.

The SAP system shows a high structural strength, mechanical stability, and self-healing capabilities. The supramolecular polymer network exhibits instant recovery of the interpolymer noncovalent interactions and even the increase in structural strength following the lifting of high-shear conditions (i.e., severe shear thinning).

In the temperature range from 282.5 (9°C) to 353.5 K (80°C), the SAP network exhibits thermal stability. In this temperature range, the strong and stable intra- and interchain interactions maintain the integrity of the supramolecular polymer and its flow viscoelastic behavior. Likewise, the SAP system demonstrated an enhanced thermal stability after 8 weeks at 90°C in high-salinity brine (8.4 wt%) compared with the thermal performance of the baseline. This further confirms that the functionality of the SAP system is upgraded at higher ionic strengths due to the formation of stronger intra- and interpolymer associations.

The SAP system rendered a 10% higher incremental oil recovery relative to the baseline system. The superior performance of the SAP network in displacing heavy oil is attributed to better mobility control properties, to the generation of a stable displacement front, the efficient and rapid control of the WOR, and an improved volumetric sweep efficiency that accelerates the production of oil. Overall, the SAP system is a straightforward formulation that offers several advantages relevant to EOR such as enhanced viscoelastic flow behavior, increased functionality in high ionic strength environments, stability to mechanical shear, and an improved thermal stability.

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