| Improving oil recovery of low permeability or ultra-low permeability reservoir is a fundamental case to ease the energy crisis. Polymer or surfactant flooding is usually applied to improve the residual oil recovery after waterflood. The intrinsic process of polymer of surfactant flooding in these reservoirs is non-Newtonain fluid displacement in microscale porous media. The capillary effect and interface phenomena of the fluids can be investigated by the fluids flowing in a single capillary tube. And Washburn equation, as the theory of the capillary displacement, has been widely used to characterize the liquid-gas or liquid-liquid displacement in capillary. In our study, we combined the power-law model with the Washburn equation, to investigate the non-Newtonian fluid flowing in the microscale capillary.In the present dissertation, many type of fluids flooding in the microscale capillary is investigated by a self-built horizontal capillary displacement apparatus. And the results calculated by the Washburn equation with the corresponding form were presented. From this model, we can find out the effect of molecular weight and capillary size on the behavior of polymer flooding, and the role of actual reservoir conditions, such as oil composition, mineral salt, solid wettability were evaluated. Based on the theory of packing parameter of surfactants, we find out a number of surfactant aggregation systems, and focused on the displacement of worm-like micelles in the microscale capillaries. The difference between polymer fluid and worm-like micelles in the thickening behavior lead to different behaviors in flowing in the microscale capillaries. The main contents of the present dissertation are followings.(1) Power-law model was introduced into Washburn equation to describe that power-law fluid flows in the capillary. The viscosity, capillary pressure and pressure gradient could be calculated by the equation.(2) In fused silica capillaries, hydrolyzed polyacrylamide (HPAM) solutions — gas displacement was investigated. The relationships between displacement rate and external pressure were measured in the capillaries with radius from 1.13 to 9.18 μm, and the effect of capillary size on the displacing viscosity of polymer solutions was discussed. The dependent of displacing viscosity with the capillary size was found. Furthermore, polymer solutions flowed as Newtonian fluid in the capillary with radius of 1.13 μm. The configuration of polymer molecule in microscale pores was characterized by rheometer, ultra-filtration, UV-Vis spectrum, laser-scattering and Transmission Electron Microscope (TEM).(3) The actual oil recovery conditions, such as decane, simulated oil (2% crude oil in kerosene), concentration of polymer, hydrophobic capillary and injected water, was respectively employed to the HPAM solutions displacement, and the influence of oil composition, concentration, solid wettability, and salinity in the polymer flow in microscale capillaries was discussed. It was found that the spontaneous displacement of polymer solution related to wettability and viscosity of the oil composition; and the displacing viscosity of HPAM solution was independent with the oil phase; electrolyte from salts compressed the coil of polymer molecule which lead to the viscosity decrease of polymer solution, with that the displacing viscosity in capillaries decreased. Effect of molecular weight, concentration, oil composition and solid wettability was also discussed from the viewpoint of capillary pressure. From the viewpoint of the pressure gradient, polymer flooding was an external pressure-driven process.(4) Based on the theory of packing parameter of surfactant, a number of surfactant aggregation systems were employed with oleate sodium, including salt induced and hydrotope induced systems. Furthermore, the systems induced by CoAZOCmIMB, as the hydrotope, were reversibly light-responsive. Worm-like micelles (WLMs) which self-assembled by the small molecules could increase the viscosity of solution as the polymer, but with different thickening mechanism. It was found that, the relationship of WLMs between displacement rate and external pressure was obviously different from the polymer. The displacing viscosity of the WLMs solution was also related to the capillary size. In the microscale capillaries, the displacing viscosity changed little even though the viscosity of bulk WLMs solution changed by thousand times. Aggregations of surfactant, such as micelle and vesicle, were also displaced in the capillaries. And in all the aggregation displacing experiments, the fluid thickened or blocked in the capillary with radius of 1.13 um, which is completely opposite to the polymer. It suggests that the different thickening mechanism leads to different viscosity change in the microscale pores. In addition, the surfactant solutions with different type of micelles could change the hydrophobic solid surface to be hydrophilic form.The presented dissertation focused on the viscosity change of polymer and WLM solutions in the microscale capillaries. The change of viscosity must be related to the micro structures of the aggregations. However the displacement system is complex and invisible for many apparatus, and we couldn’t get some direct photos or signals to show how the polymer or WLMs exist in the limited space. We hope that the development of instruments can help us to find more amazing results in the micro-world. Moreover, we have tried to investigated the displacement of biofluid in the microscale capillaries, but we find that the biofluid change so fast in vitro and sensitive to the environment. It is difficult for us to keep the properties of biofluid like blood in stable for measurements. The experimental device and practical method should be updated or improved for convenience in a later work. Uncompleted work above will receive attentions and interest from researchers in this field. |
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