Contrasting Study of Partially Hydrolyzed Polyacrylamide with Melamine Resin or Water-Soluble Phenolic Resin Gel Under Medium-Temperature and High-Salinity Conditions

Polymer gels are commonly used as profile control and water shutoff agents in oil fields to enhance oil recovery. In this study, two sets of medium-temperature and high-salinity gels were prepared with partially hydrolyzed polyacrylamide (HPAM) as the gel-forming agent, melamine resin (MR) or water-soluble phenolic resin (WSPR) as the crosslinker and nano-silica as the stabilizer, and their gelation time, strength and thermal stability were comprehensively evaluated under 90 ℃ and 41529 mg/L synthetic formation brine. The results showed that the gelation time of HPAM-MR gel and HPAM-WSPR gel was in the range of 3–118 h and 12–25 h, respectively. The two gels were in the high-strength gel class (storage modulus over 10 Pa). The thermal stability of the two gels differed considerably. The HPAM-MR gel showed a dehydration rate of 4% when aged for 45 days. While over half of the HPAM-MR gel exhibited severe syneresis after 90 days of aging, especially for the formulations with low polymer dosage and/or low crosslinker loading, the dehydration rate of which was up to 90%. In contrast, the HPAM-WSPR gel exhibited extremely excellent thermal stability, with a 3% dehydration rate after 90 days of aging and more than half of the formulations showed no water extruded when aged for 210 days. This study can provide exceptional gel-plugging agents for medium-temperature and high-salinity reservoirs and guidance for the screening of crosslinkers for gel-plugging agents.