Organic Acids In Aluminum Crosslinked Polymer Formation And Its Influencing Factors

The low-concentration, coordination crosslinked partially hydrolyzed polyacrylamide and xanthan gum aqueous solutions belong to linked polymer solution systems. After enhancing the molecular weight of polymer, improving the rheological properties, particular after the degradation of polymer caused by mechanical process, this system can be recovered by cross-link. This method can lower cost, obtain well rheological properties, shut off high-permeability formation and adjust the injection profile of water-flooding strata; moreover, the cross linking of high molecular polymer can increase the viscosity and the sweep efficiency of the water flooding, enhance oil recovery factor in polymer flooding and it has favorable application prospect on oilfield exploitation.The thesis is divided into two parts. Part one studies the formation of partially hydrolyzed polyacrylamide (HPAM) and xanthan gum (XC) linked polymer solution systems, selection of the best formula and the influence factors. Part two studies the effects of nonionic surfactant and salt on the properties of polymer. This thesis gets some innovative results and these studies will have very important theoretical and practical significance for applications of linked polymer solution systems in oil field.In Part one, the composition of partially hydrolyzed polyacrylamide (HPAM) cross-linker is determined and the optimal molar ratio between AlCl₃ and organic acid is 1.6:1. An optimal prescription is obtained using the method orthogonal design. The prescription is: HPAM l000mg L^-1, formaldehyde 800 mg L^-1, phenol 800 mg L^-1, organic acid aluminum 100 mg L^-1, pH6.0. The influences of polymer concentration, pH, temperature, water salinity on the crosslink system are investigated. The initial viscosity is lower than that of pure HPAM solution when the cross-linker is added. The viscosity increases with the ageing time, which is advantageous for the system to flood into the reservoir deepness. The processes of crosslink and de-crosslink are both fast when the crosslink temperature is high. The crosslink will process slowly as the temperature is lower, while the product crosslink system is much more stable. The optimal pH is within the range of 6-8. The viscosity of the system is unaffected with the using of mineralized water while the crosslink process is promoted. With the study of the rheology of linked polymer solution, the microscopic structure and the crosslink location, we draw a conclusion that the organic acid aluminum retards the crosslink of HPAM. It can be deduced that the crosslink behavior takes place between the functional group of -COO^- of HPAM molecule and AlOA from the analyzing of the infrared spectrum. The rheological behavior of the weak crosslink polymer gel exhibits a shear-thicking property as shown in the rheological curve, which is attributed to the existence of gel particle in the network structure of link polymer gel. As shown in the rheological curves, the linked polymer exhibits mainly elastic property with G'≥ G", and the system is belong to the linear viscoelastic fluid.We found in the crosslink between aluminum organic acid and XC that the semi-rigid rod-like structure of the XC should be destroyed to insure the crosslink. An additive of H-A can transform the structure of the XC into flexible and rotatable macromolecule first. Then the successive crosslink agent of aluminum organic acid can form three-dimensional network structure with the polymer, namely, the weak gel. Therefore, the certain of additive sequence should be implied to form the crosslinked XC. The sequence is determined as that: the XC is diluted to the desired concentration, then the H-A is added and fully mixed, next, the mixture is placed for 5-10 minutes. Then the assistant agent of Y and the aluminum organic acid are added sequentially, the solution is diluted to the desired concentration and the pH is modified to about 4.5. An optimal prescription is obtained using the method of orthogonal design. The prescription is as below: XC 1500mg·L^-1, aluminum organic acid 300 mg·L^-1, H-A 250 mg·L^-1, assistant agent H 100 mg·L^-1, pH 4.5. The influences of XC concentration, pH, temperature, water salinity on the crosslink system are investigated. The viscosity of the system is higher at the pH 4.5～5, and the weak gel is easier to formed in the system. The weak gel of XC with high salinity may keep high viscosity even for longer ageing time. The processes of crosslink and de-crosslink are both fast when the temperature is high. The weak gel is more stable at 20～40 °C than that at 60°C. When the concentration of XC is much large than 1500mg/L, the stable crosslink product can be obtained.Part two studies the interaction between polymer (polyoxyethylene ethers phosphate) and surfactant (3530s) and the effect of salt on their interaction. The results show that with increasing the concentration of polyoxyethylene ethers phosphate, the apparent viscosity of system decreased and the solutions exhibited from pseudo-plastic fluid to shear-thickening fluid gradually; appearance of two transition points in the surface tension isotherm indicates the formation of polyoxyethylene ethers phosphate/3530s complexes or the association of surfactant molecular on the polymer; the CMC of polyoxyethylene ethers phosphate is 1000ml/L investigated by surface tension and steady-state fluorescence; the influence of polyoxyethylene ethers phosphate on XC is less than that on 3530s; the concentration of cationic surfactant can not exceed 1000mg/L in dialkyl-polyoxyethe-nyl-quaternary ammonium compound/3530s system, otherwise, the flocculation will occur; with increasing the number of valence electrons of salt which has opposite electric charges of polymer chains, the salt has more effect on HPAM and the apparent viscosity of system decreased.The novelties of the thesis are as follows:1. The linked polymer solution composed of partially hydrolyzed polyacrylamide (HPAM), xanthan gum (XC) and organic acid aluminum and the best formula were found. Particular the H-A water structure-destroyed agent was found in the biopolymer xanthan gum solution which made the link of xanthan gum and organic acid aluminum possible.2. The rheological and viscoelastic properties of organic acid aluminum/HPAM linked polymer solution were studied by RS75H rheometer in macroscopic aspect. The inner structure and linked position of organic acid aluminum/HPAM linked polymer solution were studied by field emission scanning electron microscopy and fourier transform infrared spectroscopy FT-IR 5700.3. The interaction between polymer and surfactant and the effect of salt on their interaction were investigated by surface tension, steady-state fluorescence and rheological measurements which may be helpful to practical applications.