Study On Solution Properties, Structure And Flooding Application Of The Modified Xanthan Gum

The thesis is related to the shortcomings of XG that existed in the process ofapplications, such as the high dosage and the limit of temperatureresistance.Water-soluble polymer modified xanthan gum（MXG） which exhibitedintermolecular association behavior was obtained through the etherification of xanthangum.Solution properties, associating microstructure, static adsorption and floodingperformance were investigated in this paper.Compared with XG, the polymer of MXG exhibited better thickening propertiesin pure water and brine solution with5g/L NaCl. For the MXG concentration of2g/L,the apparent viscosities were303.9mPa·s and275.9mPa·s, respectively, in aqueoussolution and5g/L NaCl brine solution. In the range of0～80g/L NaCl concentration,the intermolecular hydrophobic association could be formed via the hydrophobicinteraction of the octylphenyl group; and the C-O bonds of chains could be complexwith the Na⁺. Therefore, the MXG brine solution exhibited good salt-resistantperformance and the salt-thickening behavior twice.In5g/L NaCl and60g/L NaClbrine solutions with MXG concentration of2g/L, the apparent viscosities were275.9mPa·s and281.9mPa·s, respectively, at30oC, compared with XG, the rate ofincreasing were56.3%and20%. The apparent viscosities of2g/L MXG in aqueoussolution and5g/L NaCl brine solution were still up to167.9mPa·s and151.9mPa·s at75oC. At this temperature, the apparent viscosities of XG solution corresponding to theconcentration was only84mPa·s and60mPa·s.The results of the fluorescent and UV pyrene probe showed that the mechanismsof salt resistance and heat resistance were completely different with hydrophobicallymodified polyacrylamide copolymer in aqueous solution. The intermolecularassociation was reinforced with increasing the polymer concentrations in water andbrine solutions, resulting in the enhancement of the non-polarity, the number and thesize of hydrophobic microdomains.In5g/L NaCl brine solution， although theassociation with hydrophobic groups was enhanced, the UV absorbance of the polymer in brine solution was slightly higher than the absorbance of aqueous solution,and compared with the salt-free solution, the I₁/I₃value was only a weak decline insalt solution.This revealed that the conformation of polymer chains were stillstretched in brine solution due to the six-membered ring rigid structural unitcontaining with the MXG molecular chain, resulting in a small decline of the polymerviscosity in brine solution. In the range of0～70g/L NaCl concentration, theelectrostatic shielding effect and the complexation of C-O bonds in polymer chainschanged with the change of NaCl concentration, resulting in the change ofhydrophobic association, the association tigntness and the number and the size ofassociative structure,therefore, the value of A, I₁/I₃and Ie/Imshowed irregular changes.The I₁/I₃value showed irregular oscillation change and the A value was up to themaximum twice with increasing the temperature from30to75oC. For MXG, thehydrophilicity of hydrophilic groups in the molecular chain was weaken due to thedestroy of hydrogen groups with the increasing of temperature,leading to thestrengthening of hydrophobic association and the closer of associative structure, butthe solution viscosity decreased as a result of the reducing of the association numberand size. For hydrophobically modified polyacrylamide copolymer, as the temperaturewas higher than50oC, the association between molecular chains was been weakenedand the associated microstructures were untangled,causing that the solution viscositydecreased significantly.Scanning electronic microscope （SEM） morphologies showed that the dendriticassociated microstructures were formed via the intermolecular association of theextended branched chains of MXG in water.The hydrophobic association enhancedand associated microstructures became closer with the MXG concentration increasing.The molecular chain bundles were formed in1.5g/L MXG brine solution and thecontinuous associated microstructures were still formed in3g/L MXG brine solution.It is because of the formation of associated microstructures and the rigid structure ofMXG that the grafted polymer brine solutions displayed excellent the properties.The MXG static adsorption experiments in quartz sand showed that theequilibrium adsorption capacity of MXG was lower than the equilibrium adsorptioncapacity of XG, and the influence temperature on static adsorption of MXG wascompletely different from HPAM.With the increasing of adsorption time and polymerconcentration, the adsorption capacity of MXG and XG increased firstly, anddecreased, then tended to balance.And the equilibrium adsorption capacity of MXGwas475.1μg/g, the equilibrium adsorption capacity of XG was648.2μg/g.The results of flooding experiments showed that MXG had better injectionperformance, mobility control capability and subsequent water flooding effect thanXG. In the percolation process of MXG, pressure could quickly reach balance and theresistance coefficient and residual resistance factor increased as the polymerconcentration increased. Simulated the reservoir of Daqing oil field environment:temperature（45oC）, salinity（4456mg/L）.Injecting the0.8g/L MXG to the core permeability of184.9(10^-3um²)could obtain resistancecoefficient10.8and residualresistance factor3.4. The0.4g/L MXG could be successfully injected into theminimum core permeability of52.5(10^-3um²)and btain resistance coefficient8.8andresidual resistance factor1.5. These experimental datas provided a scientific basis forthe modified xanthan gum used in middle permeability reservoir.