خصوصیات آماده سازی، ویژگی های محلول از کوپلیمرهای آکریل آمید برای بهبود عملکرد روغن Preparation, solution characteristics and displacement performances of a novel acrylamide copolymer for enhanced oil recovery (EOR)

Introduction Partially hydrolyzed polyacrylamide (HPAM) has been the most widely used polymer for EOR applications at the moment [1]. However, in the condition of high temperature and high salinity, irreversible chain scission may occur, which may cause the decrease in viscosity. So, some scholars have begun to turn their attention to develop ultrahigh molecular weight HPAM (UMW-HPAM). Although the breakage of macromolecule chain is unavoidable, the chain length after breakage of UMW-HPAM is greater than that of ordinary HPAM. Unfortunately, there is no way to improve the molecular weight of HPAM without limitation. At present the molecular weight of most UMW-HPAM is 3.0–3.5 9 107 [2]. This seems to be an extreme value. The molecular weight depends on far too many variables including the initiator concentration, temperature, the kind of solvent, monomer purity, initiation system, chain-transfer agent, and so on. It is not easy to further increase the molecular weight of HPAM using the traditional polymerization method. Besides UMW-HPAM, hydrophobically associating polyacrylamide (HAPAM) is also attracting increasing attention because of its unique viscosifying ability. HAPAM is derived from polyacrylamide by incorporating a small fraction of hydrophobic groups. In aqueous solution, the hydrophobic groups tend to associate together leading to the formation of network structure which increases the solution viscosity greatly. However, the introduction of hydrophobic groups decreases the solubility of HAPAM, which severely handicaps its application. In addition, some suitable modified monomers are copolymerized with acrylamide to yield product which would be thermally stable for a certain period of time [3]. The modified monomers include strong sulfonate electrolytes (2- acrylamide-2-methyl propane-sulfonate (AMPS) [4], sodium vinyl sulfonate [5], sodium-p-styrenesulfonate [6, 7]) and ring structure monomers (vinylpyrrolidone (NVP) [8–12], allyl-b-cyclodextrin [13, 14], chitosan [15] and so on). Compared with carboxyl group, sulfonate group would offer stronger hydrogen bonding to provide higher stability in solution. In addition, the latter has stronger hydrophilicity to improve the water-solubility of copolymer [16]. The ring structure group such as VP may decrease the thermal hydrolysis of amide group [1]. In addition, the ring monomer might provide robust steric hindrance to resist chain degradation in high temperature [15].