Synthesis and Research of AM/AMPS Copolymer

Water-soluble polymers are widely used in the tertiary oil recovery process in the petroleum industry due to their excellent viscosity-increasing and displacement effects. Among the polymers currently used for oil displacement, hydrolyzed polyacrylamide (HPAM) is the main one. However, due to the presence of carboxyl groups in the molecular structure of HPAM, these carboxyl groups are very sensitive to salts. Especially under high-temperature conditions and in the presence of high-valent metal ions, phase separation and other phenomena are very likely to occur, which significantly reduces the viscosity of the aqueous solution. Therefore, HPAM cannot be applied to high-temperature and high-salt oil reservoirs.

2-Acrylamido-2-methylpropanesulfonic acid (AMPS) is an anionic monomer with carbon-carbon unsaturated bonds in its molecule. It can introduce sulfonic acid groups into the molecule. After copolymerization with acrylamide-based monomers, the resulting copolymer can significantly improve the oil displacement effect and enhance the resistance to high temperature and high salt, thereby meeting the requirements of high-temperature and high-salt reservoir conditions. In the industrial production of polymers, the copolymer of polyacrylamide and AMPS is mainly synthesized in a reaction kettle using aqueous solution polymerization. The entire polymerization process does not involve mass or heat transfer with the outside world and is completed under approximately adiabatic conditions, hence it is called adiabatic polymerization.

The adiabatic polymerization process has relatively simple equipment, resulting in low investment, making it suitable for large-scale industrial production. However, the polymers synthesized using adiabatic reactors have certain defects, namely low relative molecular weight. Since the polymerization reaction of acrylamide (AM) and comonomers is exothermic, the released heat cannot be transferred out quickly, leading to a decrease in the molecular weight of the polymer and even the occurrence of molecular weight explosion (violent polymerization).

This process adopts the method of low-temperature initiation and a composite initiation system, which can slow down the reaction rate, reduce the impact of temperature changes on polymerization, and thus obtain high-molecular-weight and uniform copolymer products. We selected the ammonium persulfate and sodium bisulfite system as the initiator for the redox reaction, and used TMEDA, EDTA-2Na, urea, etc., as auxiliary agents. Aqueous solution adiabatic reaction was employed to synthesize the AM/AMPS terpolymer, and the structure and main properties of the copolymer were investigated. The experimental results show that reducing the initiation temperature and the amount of initiator is beneficial to the growth of polymer molecular chains. The relative molecular weight of the synthesized polymer can reach 25 million, and the copolymer has excellent solubility. When a solution prepared with fresh sewage and the copolymer was tested for viscosity at 95°C for 60 days, the viscosity retention rate was still as high as 84.2%. The evaluation of oil displacement effect under simulated reservoir conditions showed that it could increase oil recovery by 17%. Therefore, the copolymer synthesized by this process exhibits good viscoelasticity and is expected to be applied in high-temperature and high-salt oil reservoirs.