Effect Of Cyclodextrin On The Properties Of Hydrophobically Associating Polymer Solution

Due to the formation of a dynamic physical cross-linking network between hydrophobic groups,hydrophobically associating polymers has a stronger viscosity-increasing ability and better shear thinning than conventional water-soluble polymers.Currently,it has been widely used in chemical flooding fluids,fracturing fluids,drilling fluids,and other oilfield chemical working fluids,and has achieved remarkable effects.And it has solved the major technical problems of oilfield polymers such as temperature resistance,salt resistance and efficient thickening.Hydrophobically associating polymers are rapidly developing as a new field of oilfield chemicals.However,due to the interaction between hydrophobic groups,the slow dissolution rate of hydrophobically associating polymers does not meet the needs of the continuous development of oilfield development projects.The existing methods that help to accelerate their dissolution all directly impair their resistance to temperature,salt and efficient thickening cannot be applied.How to speed up the dissolution rate of hydrophobically associating polymers has become a major technical problem to be solved in the development of chemical working fluids in the oil field.Based on a systematic study of the thermodynamics and kinetics of the dissolution of hydrophobically associating polymers,the effects of the cyclodextrin and the hydrophobic groups of the polymer on the formation of inclusion complexes,the process and the law of action and its effect on the rheology of the hydrophobically associating polymer solution are studied in detail.A method have been found that can significantly increase the dissolution rate of hydrophobically associating polymers(comparable to conventional HPAM)and can retain(resume)the temperature-resistance,salt-resistant,and efficient thickening properties of hydrophobically associativng polymer.Effectively solving the problem of the solubility of hydrophobically associating polymers provides a very reliable method.It was found that the accelerated dissolving effect of cyclodextrin on the hydrophobically associating polymers is mainly in the disentanglement stage in the later period of swelling.As the molar ratio of cyclodextrin to hydrophobic group(CD:[H])increases,the time for the dissolution of the hydrophobically associating polymer logarithmically decreases.It was demonstrated by the investigation of dissolution kinetics of the hydrophobically associating polymers that the hydrophobically associating polymers have higher dissolution activation energy than polyacrylamides.Cyclodextrins are effective in reducing the dissolution activation energy of hydrophobically associating polymers.The cyclodextrins inclusion of the hydrophobic group to dissociate the association structure can reduce the viscosity and modulus of hydrophobically associating polymer solutions by two orders of magnitude.Using the inclusion properties of cyclodextrin,the structural and non-structural viscosities in the hydrophobically associating polymer solution were quantitatively calculated,and the intrinsic viscosity of the hydrophobically associating polymer was accurately determined,avoiding the influence of association between hydrophobic groups.The UV and fluorescence emission spectra were used to reflect the variation of the hydrophobic association domains in solution with CD:[H].The rheology method was used to study the inclusion process between cyclodextrin and hydrophobic associative polymers.The inclusion constants and enthalpies and entropy changes in the process were analyzed.Using the competitive inclusion characteristics of cyclodextrins,rheological properties of the hydrophobically associating polymer solution was adjusted by the addition of nonionic surfactant nonylphenol polyoxyethylene ether(NPe)with higher affinity to cyclodextrin to the solution of the hydrophobically associating polymer containing cyclodextrin.The effect of concentration of NPe and HLB value on the rheological properties of the hydrophobically associating polymer solution containing cyclodextrin was studied.Competitive inclusion interactions and polymer-surfactant interactions both play crucial roles in the recovery of rheological properties.Both of these effects are closely related to the HLB of the surfactants.NP4,NP7 and NP10 with the low HLB can completely recover and further increase the viscosity of the hydrophobically associating polymer solution.NP4 with the lowest HLB value can completely recover or further increase the solution viscosity over a wide range of additions,but NP7 and NP10 will be in excess over a narrow range of additions,resulting in viscosity decrease in hydrophobically associating polymer solution.NP12 and NP15 with highest HLB values can only partially recover viscosity of hydrophobically associating polymer solution.The inclusion of cyclodextrin mono-molecules with hydrophobic groups reduces the density of the network structure in the hydrophobically associSating polymer solution,resulting in viscosity and modulus decrease.However,the cyclodextrin polymer can form stronger network structures with the hydrophobically associating polymer in solution and increase the solution viscosity and modulus.Cyclodextrin polymers were synthesized and characterized by IR and NMR.The thermal stability of cyclodextrin polymers was studied by thermogravimetric analysis(TGA).The molecular weight and the amount of the cyclodextrin polymer and the concentration of the hydrophobically associating polymer solution have a great influence on the rheological properties of the mixed solution of the two polymers.The increasing degree of salinity can seriously reduce the viscosity and modulus of the two polymer mixed solutions.The relationship between the viscosity and the temperature of the two polymer mixed solutions has specific viscosity-temperature relationship,which is deviated significantly from the linear.