The effect of four different phenolic compounds (i.e., phenol, catechol, resorcinol, and hydroquinone) on the performance of organically cross-linked terpolymer gel systems at the temperature of 150 °C was investigated. The phenol-based gelant systems were not able to form visible bulk gels at this extremely high temperature because the cross-linked clusters between phenol and hexamethylenetetramine (HMTA) only contained a small number of hydroxyl groups for cross-linking reactions. The catechol- and hydroquinone-based gelants were able to form relatively strong bulk gels because the amount of the cross-linked clusters between these two phenolic compounds and HMTA increased significantly. This increment also contributed to the decrease of the grid sizes of the gel network structures and the emergence of dendritic structures on them, thereby significantly increasing the viscosity, storage modulus, and thermal stability of the obtained gels. However, these two gel systems could not be maintained for long; syneresis began after only 3–12 days of the systems being held at 150 °C. When phenol was replaced by resorcinol, bulk gels with excellent strength and long-term thermal stability were able to form at 150 °C. The use of the gelation mechanism of the cross-linking reactions between the terpolymer and different cross-linker systems can help researchers and petroleum engineers better understand the differences between the different cross-linker systems and thus develop more suitable polymer gel systems for water management in extremely high temperature reservoirs.

Aggregation behavior of sulfonated phenol formaldehyde (SPF) resin in presence of different valence salts and solution pH values was studied by measuring the change of dispersion turbidity with time. Electrophoretic mobility and hydrodynamic diameter of SPF resin aggregates were also measured under different salt conditions. Disaggregation behavior of SPF resin aggregates was characterized by manually shaking or ultra sound treatment. The result shows that that the size of SPF molecule aggregates and turbidity of the SPF resin dispersion were increased with the increase of Na+ and Mg2+ concentrations and accordingly, the dispersion stability of SPF resin was decreased. The effect of Mg 2+ on SPF resin molecule aggregation was more sensitive than that of Na + as Mg 2+ has stronger charge screening effect on repulsive forces between SPF resin molecules. H + protonates -O -and -SO 3 -groups on SPF resin molecules leading to decrease of surface charge on the molecule, therefore the molecule aggregation was promoted and SPF resin dispersion stability was decreased. The reversibility of SPF resin aggregates was observed. The SPF resin aggregates could be disaggregated under ultra sound treatment. In addition, the disaggregated aggregates could recover to its' original size at quiescent conditions.

Sulfonated phenol–formaldehyde (SPF) resin used as a cross-linker for petroleum reservoir conformance control was synthesized under alkaline conditions. The reaction process of SPF resin was evaluated by measuring the solution’s viscosity with respect to phenol–formaldehyde (PF) resin. The molecular structure of SPF resin was characterized by both FTIR and HPLC–MS/MS. The influence of the formaldehyde/phenol molar ratio (F/P) and the sodium formaldehyde sulfoxylate/phenol molar ratio (S/P) on the properties of SPF were analyzed in terms of the storage time, coagulation value, molecular size, and zeta potential. The results indicate that the presence of formaldehyde sodium bisulfite could slow down condensation reaction. Phenol rings were connected by methylene bridges in the position of o–p, and sulfonated SPF resin molecules all had one sulfonate group on the oligomer structure. The storage time decreased from 87 to 6 days, and the zeta potential decreased from −3.02 to −7.70 mV with the increase in F/P (1.2–2.0). Meanwhile, the sedimentation value and the diameter increased from 3.291 × 104 to 5.045 × 104 mg/L and from 2.7 to 5.3 nm, respectively. Sulfonation could significantly increase the storage time and dispersion stability. With the increase in S/P (0.1–0.35), the storage time increased from 15 to 86 days, the sedimentation value increased from 1.927 × 104 to 5.269 × 104 mg/L, and the diameter decreased from 6.3 to 3.0 nm. This paper can present new ideas for improving the storage stability and salt tolerance of phenol–formaldehyde resin and further improving the range of its applications, which has essential reference significance.

To improve the dispersion stability of phenol-formaldehyde resin (PFR) particles in simulated oilfield injection water and their propagation ability in petroleum reservoir, a hydrophobically associating polymer (HAP) was employed as a stabilizer in this paper. The dispersion stability of PFR in the injection water was studied by measuring turbidity as a function of time. In addition, the migration property of the PFR/HAP dispersion was evaluated by both cellulose membrane filtration and sand packs-flooding experiments. The results show that HAP can stabilize the PFR dispersion prepared with the simulated injection water by forming PFR/HAP complex molecular aggregates. These aggregates can migrate in sand packs with strong flow resistance due to deformation or disaggregation of the aggregates when passing through the pore throat. Oil recovery was improved by up to 21.1% on the basis of water flooding, and the higher the concentration of PFR/HAP dispersion system, the better the oil recovery effect. Moreover, the cycle of log-jamming/dispersion of the aggregates leads to their penetrations through the bigger pores in the sand packs with a higher flow resistance than water. This process can improve the conformance of water in high permeability sand packs on a micro/macro scale and thus divert more water into low permeability sand packs. Therefore, more oil could be recovered from the low permeability sand packs. Moreover, the bigger the sand pack’s permeability ratio, the lower the oil recovery rate by waterflood, and the more the incremental oil can be recovered by the PFR/HAP flood.

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