Phenolic resin gel suitable for medium-temperature and high-salinity reservoirs

Abstract

Gel has been widely applied as a plugging agent for enhanced oil recovery. In this study, partially hydrolyzed polyacrylamide (HPAM) or co-polymers of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid (AM-AMPS) cross-linked with water-soluble phenolic resin (WSPR) forming two phenolic resin gels with mineralization of 41529 mg/L at 90 °C. The properties of the two gels were systematically evaluated in this work. Under the same dosage of polymer and cross-linker conditions, HPAM gel exhibits a faster crosslinking rate and higher strength than AM-AMPS gel, but is less thermal stable than AM-AMPS gel. Part of the two phenolic resin gels was prone to premature syneresis at higher crosslinker dosages, which has not been reported in published literature. Severe syneresis was observed in the HPAM gel with the cross-linker concentration ranges from 0.8∼1.0 wt% when heated up to 60 days. Fortunately, stable gels were developed when the loading of HPAM and cross-linker in the gelant ranges from 0.8∼1.0 wt% and 0.4∼0.6 wt% respectively. Besides, the dehydration ratio of some stable HPAM gels was still less than 8% when these gels aged for 150 days. For AM-AMPS gel, syneresis was observed in the gels with 0.8∼1.0 wt% cross-linker and 0.4 wt% polymer when heated up to 120 days. Luckily, when the polymer dosage is over 0.4 wt%, the crosslinker loading had little effect on thermal stability, so some stable AM-AMPS gels can be acquired. Premature syneresis of higher cross-linker loading gels, which is counter to our goal of increasing crosslinker dosage to improve the crosslinking density and further enhance thermal stability. Based on XPS, FT-IR, and Cryo-SEM testing results, two syneresis mechanisms of the higher crosslinker gels were proposed, which ascribes to the decrease in hydrophilicity and excessive crosslinking of gel systems. A piece of advice should bear in mind when design a phenolic resin gel: keep the cross-linker dosage appropriate to avoid overloading it. As a result, our findings may guide the development of stable phenolic gels under similar conditions, and part of the two gels could provide a solution for plugging in medium-temperature and high-salinity reservoirs.