Development and property evaluation of compound cross-linking polymer weak gel system

The weak shear resistance of weak gel profile controlling and flooding system limits its application in reservoirs, we prepared a weak gel system with favorable profile controlling and flooding performance with AM/AA/NVP as the main agent and added Phenol–formaldehyde as cross-linking agent and temperature stabilizer. We studied the effects of polymer concentration, stabilizer concentration, crosslinker/polymer proportion, crosslinker concentration, temperature, pH and salinity on the gelling property. The optimum conditions for preparing the weak gel system were identified as follows: concentration of polymer (AM/AA/NVP): 2 000 mg/L; mass ratio of crosslinker/polymer: 2/1 000; proportion of crosslinker (formaldehyde/phenol): 4∶1; concentration of stabilizer: 100 mg/L; pH of the system: 7; and suitable temperature 60 ℃. The in-house evaluation on profile controlling and flooding performance shows that the system has good shear resistance, its viscosity retention rate is up to 91.38%, and its plugging rate is above 99%, its breakthrough pressure is greater than 7 MPa and has certain selective plugging capability, and the sectional improvement rate is over 80%.