Abstract
Gel syneresis is a common problem in gel treatment for oil recovery applications. In this study, a stable gel was prepared in a soft brine by using a water-soluble phenolic resin as a crosslinker, nanoparticles as a stabilizer, and partially hydrolyzed polyacrylamide (HPAM) or copolymers with different contents of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) groups as polymers. The syneresis behavior of the gels formed in a soft brine was evaluated upon aging in hard brines. The results show that when the salinity of the hard brine is lower than 30,000 mg/L, the gel expands, and its strength decreases; when the salinity of the hard brine is higher than 50,000 mg/L, the gel exhibits syneresis, and its strength increases. The effects of various influencing factors on the gel syneresis behavior were also evaluated. It was found that optimizing the polymer structure and adding nanoparticles can effectively overcome gel syneresis and enhance gel stability. Based on the research described in this paper, some proposals for designing salt-resistant polymer gels are presented.
Highlights
Polymer gels have been used in the oil field for many years to control the flow of fluids within reservoirs [1,2]
The results show that when the content of the AMPS group in the copolymer was low (e.g., AM-AMPS25, Figure 11), the gel stability in the brine was not much different from that of hydrolyzed polyacrylamide (HPAM); the gel stability was significantly improved when the AMPS group content in the copolymer was high (e.g., AM-AMPS60, Figure 12)
Through the aging experiment of gel in brine, we found that the gel formed in a soft brine would absorb water and swell in low-salinity water, while it would exhibit syneresis in high-salinity brines
Summary
Polymer gels have been used in the oil field for many years to control the flow of fluids within reservoirs [1,2]. These gels are inexpensive and easy to apply at well sites. When a gelant consisting of polymers and crosslinkers is injected into a reservoir, a viscoelastic gel will form and create a blocked area within a period of time due to elevated reservoir temperatures. The selected gel system should be compatible with specific conformance problems and reservoir conditions [11]. The gel must have enough stability under reservoir conditions to ensure that it can maintain good plugging performance. The gel may undergo processes that impair its plugging ability, such as syneresis [12,13]
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