Interaction Between Hydrophobic Modified Polyacrylamide And Block Polyethers

Hydrophobically modified water-soluble polymer (HMWSP), which contains small amount of hydrophobic groups attached along the polymer backbone, can form aggregates in aqueous solution owing to the hydrophobic effect among hydrophobic groups in HMWSP molecules. When the HMWSP molecules dissolve in water, some of hydrophobic groups may associate with each other, and form super-molecular aggregates, even net-work structures, which induce the solution with a higher viscosity. The aggregation behavior mentioned above can be destroyed with high shearing force, leading to the decrease of solution viscosity. However, when the shearing force is decreased or removed, the aggregation structures can form again, and the hydrophobic effect may be enhanced at high temperature or high salinity, as a result the solution viscosity tends to increase even under high temperature or high salinity. So, to some extent, HMWSP may overcome the deficiency of conventional polymers in sensitivity to temperature, ionic strength and shear. Therefore HMWSP has been widely used in viscosity enhancement, gel preparation, reversed-phase microemulsion preparation, solubilization, etc.The partially hydrolyzed polyacrylamide (HPAM) has been used in enhanced oil recovery (EOR) to enhance the viscosity of the displacement fluid, but temperature and salinity can obviously impact the rheological behavior of HPAM aqueous solution, except for molecular weight, hydrolyzing degree and concentration of HPAM, and HPAM solution is not applicable for EOR process in reservoirs with high temperature and high salinity. Hence, many studies are interested in hydrophobically modified polyacrylamide (HMPAM) system as well as the interaction between it and surfactant.In this thesis, the interaction between HMPAM and two block polyethers with different structure in aqueous and mineralized water solution at high temperature was investigated by rheological method. Block polyethers mentioned above are polyoxyethylene-polyoxypropylene-polyethylene-polyamine (SD-6) with branched structure and poly(dimethylsilosane)-ethoxylate/propoxylate (PSEP) with linear structure. Also the rheological behavior of HMPAM aqueous solution mixed with PSEP at room temperature was studied in order to understand the interaction between them in this condition. There are three parts in this dissertation.In the first section, the properties and application in EOR of HMPAM as well as the study progress on the interaction between it and surfactants were summarized. Also, the research significance of interaction between HMPAM and nonionic surfactant was clarified in this part.In the second section, the surface activity of HMPAM and the aggregation behavior of it in aqueous and mineralized water solution were first studied by surface tension and fluorescent spectrometry measurement, respectively. The effect of SD-6 on the rheological properties of HMPAM solutions were investigated at various time and high temperature (55 and 65℃) in order to satisfy the needs of EOR in high temperature and salinity reservoirs. Results revealed that the addition of a certain amount of SD-6 could enhance the viscosity and viscoelasticity of HMPAM solution in mineralized water, inferring that inorganic ions played the important role. Not only the weakness of intramolecular electrostatic attraction of HMPAM but also the complexation between high valent cationic (Ca2+, Mg2+) and oxyethylene group of SD-6 were favorable to enhance the viscosity and viscoelasticity of HMPAM solution. Flow characteristic and core flooding tests indicated that 1750 mg·L-1 HMPAM systems with 25 mg·L"1 SD-6 is applicable to use as a displacement system in polymer flooding process at 65℃and 8074 mg·L-1 total salinity.The third section divides into two parts. In the first part, the rheological behavior of HMPAM aqueous solutions mixed with PSEP was investigated via steady shearing and oscillatory shearing measurement. At a certain PSEP concentration, the stronger net-like structure formed as the HMPAM concentration increased. However, at a certain HMPAM concentration, the increase of PSEP concentration lead to the enhancement of the hydrophobic interaction between them, which is favorable to the formation of stronger network. However, the hydrophobic interaction among PSEP molecules was also enhanced, leading to the formation of PSEP aggregates and the breakage of the network. Also the effect of salt (MgCl2 and CaCl2 on the rheological behavior of HMPAM/PSEP mixed system was studied. Results revealed that, for the systems with low concentration salt, the electrostatic interaction between -COO- group of HMPAM and Mg2+ as well as Ca2+ might enhance the net-like structure, while for the systems with higher concentration salt, the enhanced electrostatic interaction might results in the curling of HMPAM molecular chains. In the second part, the effect of PSEP on rheological properties of HMPAM aqueous and mineralized water solution was investigated. At high salinity, the breakage of the intramolecular electrostatic attraction of HMPAM, the intermolecular bridging among -COO-groups of HMPAM owing to the high valent cations as well as the complexation between high valent cations and oxyethylene group of PSEP resulted in the stability of mixed system at 55℃. However, at higher temperature (65℃), neither the rheological properties of aqueous solution nor that of mineralized water solution was improved by PSEP. Comparing the effect of SD-6 on rheological properties of HMPAM solution with that of PSEP, it can be inferred that the block polyether with branched structure is more effective as a modifying agent of rheological properties.