| Nowadays a great deal of oil has been exploited with the increasing demand. As a result, the conventional oil sources which can be easily exploited and transported become less day by day. Consequently, the exploitation and utility of unconventional oil sources, such as high pour point and high viscosity crude oil has being regarded as one of the important energy projects in century 21.Based on the analysis of the composition and fluidity of crude oil, it can be concluded that the high pour point of crude oil is relative not only to the high wax content but also to the carbon chain length of wax and that the viscosity of crude oil is relative not only to the high colloid content but also to the high branch of wax.In order to solve the special pour-point reduction of the high pour-rpoint oil with high wax content, high pour-point above 50℃and bad impressibility to the commercial pour-point depressants in Henan oilfields, this paper was engaged in the investigation on exploring for new-style and high-efficiency pour-point depressants. In this paper, two new-style pour-point depressants, namely, copolymers and macromolecules have been purposely synthesized and characterized, the pour point depressing performance of which was studied. With the addition of 0.01% dosage and under the disposing temperature of 90℃, the synthesized copolymers SMA-al, LMZ-10 and SMA-1 made the pour-point of the high pour-point oil 14# of Henan reduced by 6℃,7℃and 8℃, and the pour depression effect of these pour-point depressants is improved in comparison with that of the commercial copolymer DAT with 5℃pour depression effect. These results show that the pour depression effect of the copolymers synthesized by us is better than that of the commercial copolymer pour-point depressants and our exploration also pave a way for the syntheses of new-style and high-efficiency copolymer pour-point depressants. It was found that the pour point depressing performance of copolymers depend on their relative molecule weights. As the composition and structure of macromolecules match the carbon chain distribution characteristic of wax in crude oil their pour point depressing performance is good. The analysis results of micrograms of wax crystals show that the size and order of wax crystals crystallized from crude oil disposed by pour-point depressants increase. The number of wax crystals in per crude oil volume becomes less with the sizes of wax crystals becoming bigger, which results in less coupling among wax crystals, and thus the gelation temperature and pour point of crude oil is lowered. The mechanism that the aggregate state of wax crystals is improved to reduce pour point by pour-point depressants is further confirmed.In order to solve the practical exploitation problems of extra-heavy oil in Henan oilfields, such as the badly heat-resistant property of existent viscosity-reducing agents, easy decomposition to lose their viscosity-reducing performance under high-temperature condition driven by steam, and other factors which badly effect the recovery ratio of crude oil, this paper was engaged in the investigation on exploring for high-temperature-resistance and high-efficiency viscosity-reducing agents. The developed viscosity-reducing agent SF has excellently high-temperature-resistance performance and show notably viscosity-reducing effect in a temperature range of 260～300℃. As the content of agent SF in extra-heavy oil emulsion attains the value of 400～2200 ppm, it can make the viscosity of extra-heavy oil 1# of Henan at 25℃reduced from 202.7 Pa-s to 162.1 mPa-s, and the viscosity-reduced viscosity meets the viscosity requirement of locale application under 200 mPa-s and for a viscosity-reducing rate of over 99.92% at 25℃. Moreover, this method has following merits: (i) operation conditions in a certain degree do less effect upon viscosity-reducing performance; (ii) the dosage of SF is less; and (iii) viscosity-reducing effect is obvious in a broad operation condition. The industry-test production and locale application of SF in Henan oilfields have been implemented. The locale test of SF in oil T4-2123 of Henan shows that the water content of the mined liquids lowers from 73.6% to 23.6%(decrease by 50%) and the ratio of oil and gas increases from 0.029 to 0.391 (increase by 0.362) compared with those of the production mined by steam without the addition of viscosity-reducing agents in oils 1-5. Clearly, the use of SF greatly improves the mined quantity, and thus the periodic yield improves. Meanwhile, the use of SF obviously decreases the water ratio and improves the mined quantity even compared with the water content of 43.4% in the production mined by steam in the addition of other viscosity-reducing agents in oil 6. The viscosity-reducing results in locale application disclose that the viscosity-reducing effect of SF is best to the crude oil from T4-2123 well, with a viscosity-reducing rate of 88.7% which is higher than those of other two competing viscosity-reducing agents A (viscosity-reducing rate of 73.6%) and B (viscosity-reducing rate of 75.6%) in market. Moreover, the viscosity of resulting extra-heavy oil emulsion only rebounds little when under the room temperature over 4 hours, which attains the requirement stability of locale application. The analysis results of micrograms of the emulsion of crude oil show that the emulsion of crude oil without addition of SF is in W/O type with most liquid drop being small liquid drop of W/O type and a few liquid drop being big liquid drop of O/W while the emulsion of crude oil with addition of SF is in O/W type with oil as dispersed phase and water as continuous phase. Thus it can be inferred that the viscosity-reducing mechanism through emulsification originate the formation of relatively stabile low-viscosity O/W emulsion which results from the distribution of viscosity-reducing agent molecules on the interface of oil and water, and thereby obtaining the viscosity-reducing effect of heavy oil and extra-heavy oil.Viscosity-reducing technique of oil-soluble viscosity-reducing agents can overcome the disadvantage of viscosity-reducing mechanism through emulsification and is a promising method. Furthermore, the exploitation of viscous and extra-heavy crude oils with little water content and pipeline transportation of dehydrated extra-heavy oil all need to adopt oil-soluble viscosity-reducing agents. However, the research and application related oil-soluble viscosity-reducing agents are very few all over the world. So viscosity reduction of the oil-soluble viscosity-reducing agents for the dehydrated extra-heavy oil in Henan is studied in this paper. Novel copolymer-sorted and macromolecule-sorted viscosity-reducing agents were synthesized and determined. The viscosity-reducing performance of the synthesized macromolecule-sorted viscosity-reducing agents FM-18, UP-16 and EY-18 is better than that of commercial copolymer-sorted fluidity improver EVA with good viscosity-reducing performance in a temperature range of 50～70℃. In the dosage of 6000 ppm, the viscosity-reducing percentages of FM-18, UP-16 and EY-18 upon oil 2# at 50℃are 84.1, 79.6 and 85.6, respectively, which are obviously higher than that of 58.7% of EVA in the same dosage. The disadvantage about copolymer EVA is that EVA with the relatively great molecular weight will swell and intertwist at higher temperature to produce viscosity-increasing effect upon crude oil. Investigation results show that exploitation for macromolecule-sorted oil-soluble viscosity-reducing agents can improve the viscosity-reducing effect at a higher temperature range (50～70℃), which will pave a new way for the realization of the long-distance transportation of dehydrated extra-heavy oil through the addition of oil-soluble viscosity-reducing agents to maintain high-efficient viscosity reduction in the practical efficient transportation temperature range (50-70℃). Based on the analyses of IR, DSC, SEM and TEM, it can be confirmed that the structure feature of colloid changes to certain extent after the addition of oil-soluble viscosity-reducing agents and the viscosity reduction mechanism of oil-soluble viscosity-reducing agents through modifying colloid to reduce viscosity is tentatively proved. The neural network prediction model of the dehydrated extra-heavy oil 2# of Henan in a whole-temperature range (80～38℃) and a higher-temperature range (80～50℃) was established according to the two effect factors, temperature and shear rate. It can relatively accurately predict viscosity value of pipeline-transported crude oil with relative errors of 0.177 and 0.293, respectively. It is worthy to popularize use in pipeline-transported dehydrated extra heavy oils by heating or adding agents to reduce viscosity. |
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