| An emulsion is a colloid which is a mixture of two or more liquids, such as oil and water, which do not naturally mix together. The oil and water mixing system can be divided into macroemulsion, nanoemulsion and microemulsion according to the particle size and the thermodynamic stability. The microemulsion has the characteristics of thermodynamic stability, small particle size, low interfacial tension and strong ability of solubilization, which can be used in the fields of repairing formation damage, well-cleaning fluid and treatment of oily waste. The macroemulsion is a colloid that has a greater droplets size and less mass of surfactants. As the surfactant solution injecting, the crude oil with high viscosity can form the O/W emulsion with low viscosity that means it has an excellent application prospect in the process of oil exploitation and pipeline transportation.The background and the significance of the study was introduced in the first chapter, which is the introduction of the while thesis. I studied the preparation of the temperature-insensitive microemulsion and switchable emulsion and their application in oil field. Firstly, in the chapter, the basic concept, formation mechanism and properties of micromulsion were introduced and the research progress in the field of petroleum engineering was summarized. Secondly, the switchable surfactants and the research progress in recent years were summarized.We focused on the advantages and disadvantages of CO2-switchable surfactant and discuss the characteristics of controlling the stability of the emulsion that decrease the viscosity of crude oil by emulsification and separation of the water by demulsification would be easy.The treatment of the formation damage and oily waste with microemulsion was studied in the second chapter. For the formation damage in a well, I prepare a temperature-insensitive microemulsion to deal with the high temperature in the formation conditions. The micrormulsion was prepared with APG and Peregal 025 as surfactants and n-butyl alcohol as a co-surfactant. The effects of temperature, salts concentration,acids concentration on the phase behavior and solubilization capacity of the microemulsion were studied in this chapter. As a result, we drew the pseudoternary phase diagram and found the resistance of temperature(from room temperature to 100℃), salts(from 0 to 30 wt% CaCl2),acids(from 0 to 9 wt% HCl) and controlled its density from 1.0 to 1.3 g/cm3 by adding salts. Because of the properties of the microemulsion, it may adapt to the complex formation conditions. The interfacial tension and contact angle was measured and the ability of treating formation damage was deduced by the bottle test of removing interface wettability reversal, oil-based mud damage, asphaltene precipitation. In the process of treatment, we studied the effect of temperature on the interfacial tension and cleaning ability, that the interfacial tension decreased and the cleaning ability was enhanced with the increase of temperature. At last, the oily sludge and oily drilling cuttings were treated with the microemulsion at room temperature and the oil rate decreased to below 2% that the there was a good cleaning ability in the treatment.In the third chapter, the switchable emulsion and its application were studied. Using sodium oleate as surfactant, the carbon dioxide switchable ability of surfactant solution was studied. Bubbling with carbon, the pH decreased and then the pH increased after bubbling nitrogen under heating. The effect of HLB value and salinity on the stability of emulsion was studied that the emulsion was prepared with sodium oleate and oleic acid. We bubbled carbon dioxide into the stable emulsion and the emulsion demulsified rapidly and then we studied the carbon dioxide response of the emulsion by means of microscope, zeta potential, pH meter. We bubbled nitrogen under heating into the broken emulsion and the emulsion recovered stability. We could circled the responsive progress 3 times, and we found it was a carbon dioxide switchable emulsion that the surfactant solution might have the possibility of recycling. At last, we thought the sodium oleate could be used for crude oil emulsification and demulsification process by emulsifying diesel oil and heavy oil and forming a switchable emulsion. |
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