The Research Of Interaction Between Alkali And Crude Oil In The Complex Recovery Oil System

For the ASP (alkaline-surfactant-polymer) flooding, the cooperation of the three displacement agents not only upraises the washing efficiency of crude oil but also enlarges the sweeping volume of flooding phase, therefore, the recovery percentage of crude oil grows up considerably. Nowadays, the technology of ASP flooding has been successfully explored in the precursor experiments in Daqing oilfield, which will be spread for the in-situ application in near future.In ASP flooding systems, the alkaline agents have an appeal for enhanced oil recovery because of their low cost and favorable performance. Nevertheless, the choice and dosage of alkaline agents has been remaining complex, due to their interactions with other species in the chemical slug but also with the crude oil, reservoir water, and/or reservoir rock. Therein the interaction between alkaline agent and crude oil is necessary and useful, forming surface active species for oil displacement. In this thesis, sodium carbonate (Na₂CO₃) and sodium hydroxide (NaOH) was used as the alkaline chemicals, at the same Na₂O content, to investigate the oil/water interfacial reactions between the Daqing crude oil and the alkaline solutions. Moreover, oleic acid, porphyrin, wax or the mixture of ethyl acetate and phthalic acid diethyl ester were added into the oil phases, respectively, to facilitate the studies of the interfacial interactions and to compare the functional effectiveness of alkalis.All of the thesis works are divided into five parts. In chapter I, the research background was introduced, and the relative research papers were summaried. To investigate the functional effectiveness of an alkaline agent in ASP flooding system, the relative active-species should be extracted from the crude oil first. Then the methylation and the consequent characterization of the extracted acidic fractions were conducted. The main results in Chapter II showed that the acidic extracts from Daqing crude oil comprised of alkyl dimethyl acids, aromaticity dimethyl acids and alkyl acids.In this thesis, the oil phase used was the model oil, namely, the mixture (1:1, v/v) of the degassed crude oil and the commercial kerosene, possessing a viscosity of 10.5 mPa.S at 45°C to simulate the basic fluidity of the underground oil in Daqing oil field. By considering the relative content of extracts and the acidic number of crude oil, oleic acid, the mixture of ethyl acetate and phthalic acid diethyl ester were selected as the polar additives, respectively, to conduct the influence of different polar mixtures on alkaline consumption. The results Chapter III showed that: Na₂CO₃ reacted slowly and partly with the acid components in crude oil, while NaOH did it very fast and completely. Interestingly, Na₂CO₃ is better than NaOH in lowering the oil/water interfacial tension (IFT), due to its buffer effect.Another basic parameter of the Daqing crude oil is the highly waxy. First, wax crystallization from crude oil was performed, then, the model oil of hexane and waxy extracts was used to measure the interfacial tension between the oil phase and an alkaline solution. The results in Chapter IV indicated that latent alkali of Na₂CO₃ was better than NaOH in lowering the oil/solution interface tension. Interestingly, it was found that the higher the waxy content, or the waxy crystallites, in oil phase, the lower value of the interface tension.Generally, the produced liquids after chemical flooding are very difficult to demulsify. The presence of surfactant, polymer and/or alkali in produced solutions helps the formation of W/O or O/W emulsion after ASP flooding. First, the experimental apparatus was set up and shown in chapter V. Then, the relative parameters for emulsion destruction were measured, basing on the rupturing (or, vanishing) times of the liquid films. The functional effectiveness of alkalis was presented, at the mean time, the effects of surfactant and polymer on the intensity of liquid film were also discussed.