Study On The Synthesis And Properties Of The Heat And Salt Resistant Acrylamide-based Copolymers

At present, most of the oil reservoirs are of high temperature and high salinity in EOR. In view of this, polymers used in oil field must have effective thickening properties, temperature tolerance, brine tolerance and resistance to shear force in order to achieve the ideal effect. But how to further improve the properties of the polymers to make them adapt to the need of the EOR better, the corresponding theories are not perfected, leading to the blindness in the improvement of the heat and salt resistant polymers. As such, the heat and salt resistant polymers and its solution properties have been in the focus of considerable research at present in both academic and industrial laboratories. The thermal resistant and salt-tolerant properties of the polymers can be improved by introducing some special functional structure units into the polymers, such as salt-tolerant compounds and associative compounds, etc.. Based on the above considerations, the purpose of this dissertation is focused on synthesis and characterization of thermal resistant and salt-tolerant copolymers, study of the solution properties of the thermal resistant and salt-tolerant copolymers and their practical applications. The main work and experimental results are as follows:1.Copolymers containing sulfobetaine (P(AM/DMAPS)) were synthesized by aqueous copolymerization of acrylamide with 3-[N-(2-methacroyloylethyl)-N,N-dimethylammonio]-propane sulfonate. The structures of the P(AM/DMAPS) were confirmed by 1H-NMR, FT-IR and elemental analysis. Aggregation and disaggregation of P(AM/DMAPS) copolymer in aqueous solution as a function of copolymer concentration, added salts, temperature and aging time were studied by dynamic laser light scattering and gel permeation chromatography combined with laser light scattering. It was found that P(AM/DMAPS) copolymers exist as a mixture of individual chains and inter-chain aggregation in deionized water. At low copolymer concentrations (below 1.0g.L-1), the intra-chain aggregation is dominant. With increasing copolymer concentration, the inter-chain aggregation is enhanced. The addition of a small amount of salts (NaCl,NaBr,NaI,MgCl2,CaCl2,) leads to the disaggregation of the intra- and inter-chain aggregation. Further addition of salts results in the enhancement of inter-chain aggregation. The increase of temperature from 25℃to 60℃facilitates the breakup of intra-chain aggregation and the enhancement of inter-chain aggregation. The addition of P(AM/DMAPS) copolymers to AP-P4 and SNF solutions greatly improved the thickening properties and thermal stability of AP-P4 and SNF solutions.2. Acrylamide-based, hydrophobically modified polysulfobetaines (ADS) containing 3-[N- (2-methacroyloylethyl)-N,N-dimethylammonio]-propane sulfonate (DMAPS) and varying amounts of the hydrophobic monomer stearyl methylacrylate (SMA) were synthesized by micellar copolymerization. The structures of ADS were confirmed by 1H-NMR, FT-IR and elemental analysis. The basic physico-chemical properties of the synthesized copolymers were studied by means of surface tension, dynamic laser light scattering and rheological measurements. All the copolymers showed surface activity when the copolymer concentration was above 0.07wt%. The dynamic laser light scattering measurement revealed that both zwitterionic and hydrophobic associations were important in copolymer aggregation. The rheological properties of the copolymers in aqueous solution depend on the content of hydrophobic monomer, the copolymer concentration and the addition of salt, which are characteristic of hydrophobically modified polyacrylamide and acrylamide-based polyzwitterions. The critical aggregation concentration of the copolymers is in the range of 0.07-0.1wt%. The addition of ADS copolymers to AP-P4 solutions greatly improved the thickening properties and thermal stability of AP-P4 solutions.3. Acrylamide-based, hydrophobically modified polymers (P(AM/DMDAAC/ SMA)) containing N,N-dimethyl -diallyl ammonium chloride (DMDAAC) and varying amounts of the hydrophobic monomer stearyl methylacrylate (SMA) were synthesized by micellar copolymerization. The structures of the P(AM/DMD AAC/SMA) were confirmed by 1H-NMR, FT-IR and elemental analysis. The basic physico-chemical properties of the synthesized copolymers were studied by means of gel permeation chromatography combined with laser light scattering, surface tension, dynamic laser light scattering and fluorescence measurements. It showed that in 0.1mol.L-1 NaCl solution, the intra-chain aggregation is dominant at low copolymer concentrations (below 0.5mg.mL-1); with increasing copolymer concentration, the inter-chain aggregation is enhanced. Addition of salt resulted in shrinkage of polymer aggregates as a result of neutralization of the charges and enhancement of the hydrophobic association as a result of making the polarity of the solution stronger at the same time. The average hydrodynamic radii Rh increases first and then decreases with increasing polymer concentrations in salt-added solutions. The polymer solutions exhibit a sharp increase in the average hydrodynamic radii Rh with increasing temperatures in salt-added solutions. The copolymer solutions have high surface activity and low hydrophobic polarity.4. A series of fluorocarbon modified poly(acrylamide)s (P(AM/PFHEA)) containing low amounts (0.1-1.5mol%) of fluorocarbon (CF3(CF2)5—) are synthesized by copolymerization of acrylamide (AM) with 2-(perfluorohexyl) ethyl acrylate) (PFHEA). The structures of the P(AM/PFHEA) were confirmed by 1H-NMR, 19F-NMR, FT-IR and elemental analysis. The dynamic surface tension results show that the efficiency and effectiveness of the copolymers to lower surface tension increase with increasing the fluorocarbon content in the copolymer concentration of 0.001wt%-1.0wt%. The critical association concentration of the copolymers is about 0.7wt%. The results of surface dilational viscoelasticity show that with the increase of the fluorocarbon content, the dilational viscoelasticity increases at low copolymer concentration, but firstly increases and then decreases at high copolymer concentration. Furthermore, temperature has effect on the dilational viscoelasticity of the adsorbed layer in different extents.5. Acrylamide-based, hydrophobically modified polymers (P(AM/DMAPS/PFH EA)) containing 3-[N-(2-methacroyloylethyl)-N,N-dimethylammonio]-propane sulfo-nate (DMAPS) and varying amounts of the hydrophobic monomer 2-(perfluorohexyl) ethyl acrylate (PFHEA) were synthesized. The structures of the P(AM/DMAPS/ PFHEA) were confirmed by 1H-NMR,19F-NMR, FT-IR and elemental analysis. The basic physico-chemical properties of the synthesized copolymers were studied by means of surface tension, dynamic laser light scattering and resonance scattering spectral measurements. All the copolymers showed high surface activity and increased with the increase of PFHEA content. The dynamic laser light scattering measurement revealed that the intra-chain aggregation is dominant at low copolymer concentrations (below 0.1mg.mL-1); with increasing copolymer concentration, the inter-chain aggregation is enhanced. The addition of various salts favored the intermolecular association. The addition of ADS copolymers to AP-P4 or SNF solutions greatly improved the thickening properties and thermal stability of AP-P4 or SNF solutions.