| The self-assembly systems of hydrophobically modified polymers and wormlike micelles have raised much attention in recent years, due to their excellent viscoelasticity. However, the behaviors of self-assembly systems solutions composed of high concentration of wormlike micelles and low concentration of polymer have been less reported, as well as the effect of the structure of hydrophobically modified polyacrylamide (HMPAM) on its self-assembling effect with wormlike micelles. This thesis mainly focused on these two aspects mentioned above, in order to have a further insight of the self-assembly system of hydrophobically modified polymers and wormlike micelles. On the basis of their excellent viscoelasticity and hydrocarbon responsiveness, we propose an idea to apply the self-assembly systems as fracturing fluids and expect to obtain a new low-damage fracturing fluid system with better performances.A series of HMPAMs were firstly prepared via the free-radical copolymerization of acrylamide and a surface-active hydrophobic monomer, and the self-assembly systems of20mmol/L cetyltrimethylammonium bromide/sodium salicylate wormlike micelles and HMPAM were then constructed. Rheological experiments were conducted to investigate the solution behaviors of the self-assembly systems and the effect of HMPAM structure on its self-assembling effect with wormlike micelles. At last, a self-assembly fracturing fluid system was constructed and its relevant properties as fracturing fluid were evaluated according to the standards.Results showed that with increasing concentration of HMAPM, the viscoelasticity of the self-assembly system increased as well, but the proportion of the elastic modulus had gradually declined on the contray and the rheological behaviors were also gradually deviated from the Maxwell model. The self-assembly systems exhibited good shear thinning and shear recovery property and were more sensitive to temperature and shear, but they still possessed a higher viscosity value at the same shear rate and temperature because of a more intensive network structure. Kerosene prompted the conversion of wormlike micelles to spherical micelles which completely destroyed the self-assembly network structure, however, n-hexanol induced the wormlike micelles converting into vesicles and networks were formed between the HMPAM and vesicle, thus the system remained to be viscoelastic.Since the size of the linear HMPAM meeted the demands to form "effective crosslink" with the wormlike micelles, the molecular weight of HMPAM will no longer significantly affect the density of the self-assembly networks, but the higher the molecular weight, the more obviously the rheological behaviors of the self-assembly suystem would deviate from the Maxwell model. With increasing content of hydrophobes in the liner HMPAM, the density of the self-assembly networks would increase as well, nevertheless, if the content is excessive, the probability of forming "noneffective crosslink" would also increase, which would lower the network density on the contary. During the synthesis processing, reducing the length of the micro blocks of the hydrophobe, adopting the hydrophobic monomers with longer hydrophobic chains and increasing the degree of branching of HMPAM would be efficient methods to enhance the self-assembling effect between HMPAM and wormlike micelles.The self-assembly fracturing fluids exhibited an improvement in temperature resistance of about20-30℃higher than the traditional clear fracturing fluids and they could also break gels automatically and thoughly when contacting with hydrocarbons. Core damage tests showed that the self-assembly fracturing fluids had a very close damage rate to the traditional ones, thus they could also be taken as a new kind of low-damage rate fracturing fluid system. Compared with the traditional clean fracturing fluids, the self-assembly ones would require a lower consumption of surfactant which would help to reduce the cost and control the potential reservoir damages and enviromental contaminations. |
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