Investigation of Polyvinyl Alcohol–Phenolic Aldehyde–Polyacrylamide Gel for the Application in Saline Oil Reservoirs for Profile Modification

Polymer gels are widely used in the oil and gas industry, and high-molecular-weight polymer gels have significant effects on reservoir water plugging operations. Based on nontoxic polyvinyl alcohol (PVA), its stability in solvents containing formation saltwater (Tahe oilfield, NW China) was studied, and the composite gel solution was prepared using saltwater. The polymerization mechanism of PVA with phenolic resin (PF) and polyacrylamide (PAM) was analyzed, using hexamethylenetetramine (HMTA) instead of formaldehyde for cross-linking, and the rheological properties of the prepared gel were tested; the results showed excellent elastic properties. The application value of the gel was evaluated by gelation performance, thermal stability, and indoor simulated core displacement. The gelation time of the PVA/PAM/PF gel at 130 °C was 4 h; after aging at 130 °C for 40 days, the gel strength of the polymer gel remained at the G level, and no dehydration occurred. The simulated core plugging results showed that the breakthrough pressure was 11.79 MPa and the plugging rate was 99.83%. Compared with the PAM/PF gel, the PVA/PAM/PF gel has a higher breakthrough pressure, which is beneficial to reduce the permeability of the porous medium.