**Author details**

These injectivity and propagation parameters can be obtained by continuous rheological

• have controllable gelation times, preferably greater than 2 hours, to avoid overloads in the unit's pumping system during the injection of the gelant in the reservoir. Furthermore, the gelation time must be long enough for the gelling system to reach the proposed targets (highpermeability zones or anomalies). This injectivity and propagation parameter parameter can

• form strong hydrogel under reservoir conditions-with Sydansk's gel-strength code > G (bottle testing, **Figure 3**), elastic modulus (G'), and viscous modulus (G") ratio above 10 (G'/G" > 10) with G' and G" being independent of the oscillation frequency, and G' > 1 Pa. These blocking-ability parameters can be obtained by bottle tests and oscillatory rheologi-

• provide permeability reduction factor (PRF) above 1 after the matrix treatment with the hydrogel. This blocking-ability parameter can be obtained by core flooding experimental tests [78].

Other parameters that should also be considered during the screening are the toxicity and cost of the gelling system components, as well as their thermal, mechanical, and biological stabil-

A large amount of gelling polymer systems applicable for the conformance-improvement treatment of heterogeneous oil reservoirs is commercially available or under academic development. Choosing the most suitable hydrogel for a conformance problem should be done taking into account the temperature, salinity, and hardness of the reservoir, as well as the pH of the injec-

**Figure 3.** Bottle testing characterization of PAM-PEI hydrogels using the Sydansk's gel-strength code.

Other parameters that should also be considered are the presence of carbon dioxide (CO<sup>2</sup>

the target region, reservoir mineralogy and lithology, as well as toxicity and cost of the gelling

S), the adsorption of the chemicals on reservoir rock, the permeability of

) or

be obtained by bottle tests and continuous and oscillatory rheological tests [45];

tests [56, 84, 85];

80 Hydrogels

cal tests [9, 20, 42, 56, 86];

**4. Conclusion**

tion water.

hydrogen sulfide (H<sup>2</sup>

system components.

ity, retention, and adsorption on reservoir rock.

Fernanda G. C. Tessarolli\*, Ailton S. Gomes and Claudia R. E. Mansur

\*Address all correspondence to: fernandagcordeiro@gmail.com

Institute of Macromolecules (IMA), Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro, RJ, Brazil
