The viscoelastic behavior of HPAM solutions and its effects on oil recovery were studied by means of core flowing tests and mathematical modelling. The mechanism of improving displacement efficiency due to viscoelastic effects was explained. This paper first presents a method to determine the first critical velocity (or critical viscoelastic velocity), Vce, at which the straining flow occurs. The experimental results indicated that the Vce increases with increasing permeability of porous media. Vce less than 1 m/d was observed. There is a second critical velocity (or critical transit velocity), Vcr, at which the rheological behavior of HPAM solution transits from pseudoplastic to dilatant behavior. Vcr can be also determined through experiments. Vcr ranges from 1.74 to 3.30 m/d and also increases with increasing permeability of cores in our experiments. Within the range from Vce to Vcr, elongational flow occurs although the HPAM solution still exhibits pseudoplastic behavior. Beyond Vcr, the strain viscosity increases rapidly with velocity and straining flow governs the flow behavior. The results from core flowing tests showed that the displacement efficiency evidently increases with the velocity beyond Vce and reaches a maximum when the velocity approaches Vcr. The model index B (renamed Han's index in this paper) describing the viscoelasticity of HPAM in porous media has been proved to be the relaxation time for HPAM molecules. The effect of property parameters of both porous media and polymer solution on Han's index, H, was investigated by core flowing tests with artificial cores. The property parameters include injection rate, salinity, hydrolysation degree of HPAM and core permeability. A comprehensive Han's index, Hc, was obtained as a function of these parameters by using multi-variable regression. Polymer flow tests m cores showed that the relative increment of displacement efficiency varies with Hc as a normal distribution function, i. e., there exists a optimum Hc which leads to a maximum of the oil recovery. To investigate the influence of the rheological behaviour of HPAM on the prediction of oil recovery in polymer flooding, one dimensional numerical simulation was conducted. It is believed that viscoelastic behaviour will inevitably occur during HPAM solution flushed through oil formation and it plays an important role in oil recovery. Viscoelastic property of polymers should be considered as a screening criterion and it is necessary to take into account the viscoelastic effect in polymer flood numerical simulation. P. 597
The specific structure and diverse properties of hybrid organic–inorganic perovskite materials make them suitable for use in photovoltaic and sensing fields. In this study, environmentally stable organic–inorganic hybrid perovskite luminescent materials using Pb–MOF as a particular lead source were prepared using a mechanochemical method. Based on the fluorescence intensity of the MAPbBr3/MOF composite, the mechanized chemical preparation conditions of Pb–MOF were optimized using response surface methodology. Then, the morphological characteristics of the MAPbBr3/MOF composite at different stages were analyzed using electron microscopy to explore its transformation and growth process. Furthermore, the composite form of MAPbBr3 with Pb–MOF was studied using XRD and XPS, and the approximate content of MAPbBr3 in the composite material was calculated. Benefiting from the increase in reaction sites generated from the crushof Pb–MOF during mechanical grinding, more MAPbBr3 was generated with a particle size of approximately 5.2 nm, although the morphology of the composite was significantly different from the initial Pb–MOF. Optimal performance of MAPbBr3/MOF was obtained from Pb–MOF prepared under solvent-free conditions, with a milling time of 30 min, milling frequency of 30 Hz and ball–material of 35:1. It was also confirmed that the mechanochemical method had a good universality in preparing organic–inorganic hybrid perovskite/MOF composites.
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