536 DOI 10.1007/s12182-010-0105-x Syntesis and evaluation of an oil-soluble viscosity reducer for eavy oil Guo Jixiang 1, Wang Heyi 2, Cen Caogang 3, Cen Yun 4 and Xie Xiaoai 5 1 Enanced Oil Recovery Researc Center, Cina University of Petroleum, Beijing 102249, Cina 2 Researc Institute of Saanxi Yancang Petroleum(group) Co. Ltd, Saanxi 710075, Cina 3 Nortwest Oilfield Branc Engineering and Tecnology Institute of Sinopec, Urumci 830011, Cina 4 Tua Oilfield, Hami, Xinjiang 839009, Cina 5 Yumen Oilfield Yaerxia Open Area, Gansu 735019, Cina Cina University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg 2010 Abstract: To reduce te viscosity of igly-viscous oil of te Tae oilfield (Xinjiang, Cina), an oilsoluble polybasic copolymer viscosity reducer for eavy oil was syntesized using te ortogonal metod. Te optimum reaction conditions are obtained as follows: under te protection of nitrogen, a reaction time of 9, monomer mole of reaction materials of 3:2:2 (Te monomers are 2-propenoic acid, docosyl ester, maleic anydride and styrene, respectively), initiator amount of 0.8% (mass percent of te sum of all te monomers) and reaction temperature of 80 ºC. Tis syntesized viscosity reducer is more effective tan commercial viscosity reducers. Te rate of viscosity reduction reaced 95.5% at 50 ºC. Infrared spectra (IR) and interfacial tensions of eavy oil wit and witout viscosity reducer were investigated to understand te viscosity reduction mecanism. Wen viscosity reducer is added, te molecules of te viscosity reducer are inserted amongst te molecules of crude oil, altering te original intermolecular structure of crude oil and weakening its ability to form ydrogen bonds wit ydroxyl or carboxyl groups, so te viscosity of crude oil is reduced. Field tests of te newly developed oil-soluble viscosity reducer was carried out in te Tae Oilfield, and te results sowed tat 44.5% less ligt oil was needed to dilute te eavy oil to acieve te needed viscosity. Key words: Oil-soluble, viscosity reducer, eavy oil, syntesis, evaluation 1 Introduction Heavy oil makes up a fairly large proportion of oil resources around te world. Reserves of eavy oil, extraeavy oil and natural aspalt all over te world are about 100 10 9 t (Lv et al, 2005; Dai et al, 2004). Wit te depletion of ligt oil reserves and te improvement of oil production tecnology, te proportion of te eavy oil recovery will increase in te 21st century (Sun and zang, 2005; Liu et al, 2005). Te eavy oil recovery tecnology in Cina as been developing rapidly since 1960s. Up to now, tecnologies for eavy oil termal recovery including steam stimulation and steam drive metods, and tecnologies for eavy oil cold production including alkaline drive, polymer drive and miscible flooding, ave been developed and widely used (Fan et al, 2007; Zou et at, 2007). Most of te tecnologies ave been widely applied in eavy oil development and acieved good results. Because of te ig viscosity, ig density and poor fluidity of eavy oil, reducing viscosity as become te key in eavy oil exploitation, transportation and *Corresponding autor. email: guojx002@163.com Received April 8, 2010 refining. At present, te main ways to reduce te viscosity of eavy oil are termal recovery (by means of eating cables, electric eating oil-pumping rod, and eat-conducting oil ), dilution metod by using ligt oil, viscosity reduction by emulsification and so on. Among tese metods, te termal recovery is relatively mature and as better effect, but because of its ig electricity consumption te cost is ig (Cang and Zang, 2006; Cen et al, 2004). Te tin oil dilution metod as no effect on te post-treatment of recovered fluid, owever, it can cause a waste of tin oil and its production cost is ig (Zang et al, 2006). Te density of Tae crude oil is between 0.9950 g/cm 3 and 1.099 g/cm 3, wit an average value of 1.0094 g/cm 3. Te kinematic viscosity (50 ºC) of Tae crude oil is between 48,170 mpa s and 1,800,000 mpa s, and te freezing point is between 8 ºC and 60 ºC, wit an average value of 33 ºC. So te crude oil of Tae oilfield is eavy oil. Te oil-soluble viscosity reducer can be added directly, avoiding post-processing problems wic occur in viscosity reduction by emulsification. However, te rate of viscosity reduction of eavy oil by te existing commercial oil-soluble viscosity reducers is not satisfactory, and te study of oil-soluble viscosity reducers is rarely reported abroad and in Cina work as progressed slowly (Wu and Guo, 2003).
537 In addition, te oil-soluble viscosity reducer can work well only wen it interacts well enoug wit colloid and aspalt molecules of eavy oil, and te conditions at te bottom of te wells ave great effect on its application. Up to now, we ave not found reports of eavy oil recovery by viscosity reduction wit only oil-soluble viscosity reducer (Zang, 2006; Wang, 2006). So it was urgent to develop a suitable oilsoluble viscosity reducer for Tae eavy oil. In tis paper, an oil-soluble viscosity reducer was syntesized and its properties evaluated, and it was found tat te syntesized oilsoluble viscosity reducer is more efficient tan commercial ones. Field testing of te new developed oil-soluble viscosity reducer was carried out in te Tae Oilfield of Xinjiang. 2 Experimental 2.1 Reagents and instruments TK1074 and TK1232 crude oil were from te Tae oilfield (Xinjiang, Cina), and formation water was from te 21/5 well station of Tae oilfield; Metyl stearate, etyl stearate and vinyl acetate were all analytically pure. Kerosene (wit an interfacial tension of 46.61 mn m -1 ) was treated by silica gel, and pentane, benzene, etanol, petroleum eter (90-120 ºC) were all analytically pure. TK1074 Tae model oil was made by using te kerosene as solvent and TK1074 Tae crude oil as solute wit a mass fraction of 10%. Instruments: MAGNA-IR 560 Infrared spectrometer (Nicolet Co., USA), Datapysics DCAT-21 interfacial tensiometer (Datapysics Co., Germany), SVR S interfacial viscoelastic meter (Kyowa Kagaku Co. Ltd., Japan), and Haake RV2 viscometer (HAAKE Co., Germany). 2.2 Syntesis of oil-soluble viscosity reducer Using te four factors and tree levels ortogonal test metod (see Table 1), te monomer, initiator amount, reaction temperature and reaction time were all optimized and oil-soluble viscosity reducers (terpolymer, quadripolymer 1, quadripolymer 2 and quadripolymer 3) were syntesized under te optimum conditions. In tis section, te quadripolymer s monomers are 2-propenoic acid, docosyl ester, maleic anydride,styrene and acrylamide, respectively,wile te terpolymer s monomers are 2-propenoic acid, docosyl ester, maleic anydri de and styrene. Te initiator is ADMVN and te solvent is metylbenzene. 2.3 Determination of interfacial tension Te influence of different concentns of oil-soluble viscosity reducer on te interfacial tension between TK1074 Tae model oil (wit a mass fraction of 10%) and formation water was determined at 25 ºC wit Datapysics DCAT-21 interfacial tensiometer. 2.4 Determination of interfacial sear viscosity Te interfacial sear viscosity of TK1232 crude oil in formation water was measured wit SVR-S interface viscoelastic meter. Levels Table 1 Ortogonal test table ºC Factors dosage, wt% Reaction time Level 1 3:1:1 70 0.6 8 Level 2 3:2:1 80 0.8 9 Level 3 3:2:2 90 1.0 10 2.5 Evaluation of oil-soluble viscosity reducer Te viscosity of eavy oil from Tae oilfield was measured according to Cina petroleum industry standard SY/T 5767-2005 Tecnical specification for practice of transporting crude oil treated wit pour point depressants troug pipeline and SY/T 0520-2008 Viscosity determination of crude petroleum Equilibrium metod by rotational viscometer. Te measurement is carried out at 50-90 ºC. Te rate of viscosity reduction is calculated as follows: 1 2 % 100 1 were ε μ % is te rate of viscosity reduction; μ 1 is te apparent viscosity of crude oil, mpa s; μ 2 is te apparent viscosity of viscosity-reduced crude oil, mpa s. 3 Results and discussion 3.1 Results of ortogonal tests Oil-soluble viscosity reducers were syntesized under different reaction conditions sown in Table 1. Te rate of viscosity reduction of TK1232 crude oil was studied at different conditions (w (mass of ligt oil):w (mass of eavy oil)=0.4:1, and te amount of viscosity reducer was 1% of te total mass of tin and eavy oils) to get te optimum reaction conditions. Te results are sown in Table 2. Te initiator amount is te percentage of te te total mass of monomers (except solvent). Project Table 2 Ortogonal test results (T), ºC wt% Time (t) reduction at 50 ºC % 1 3:1:1 70 0.6 8 56.7 2 3:1:1 80 0.8 9 72.0 3 3:1:1 90 1.0 10 57.3 4 3:2:1 70 1.0 10 73.3 5 3:2:1 80 0.8 8 74.7 6 3:2:1 90 0.6 9 65.3 7 3:2:2 70 1.0 9 78.7 8 3:2:2 80 0.6 10 73.3 9 3:2:2 90 0.8 8 76.0
538 According to te above Table, analyzing te experimental results. In Table 3, K 1, K 2, K 3 respectively stand for te sum of corresponding rate of viscosity reduction of te four factors and tree levels of experiments; k 1, k 2, k 3 is te average value of K 1, K 2 and K 3, respectively. Project Table 3 Analysis of ortogonal test results (T), ºC wt% Time (t) K 1 186.00 208.7 195.3 207.3 K 2 213.3 220.0 221.3 216.0 K 3 228.0 198.7 210.7 203.9 k 1 62.0 69.6 65.1 69.1 k 2 71.1 73.3 73.8 72.0 k 3 76.0 66.2 70.2 67.9 Range of k 14.0 7.1 8.7 3.9 Table 3 sows tat te influence of eac factor on te rate of viscosity reduction in view of te range is in te order of monomer >amount of initiator>reaction time>reaction temperature. Te optimum conditions for syntesizing te viscosity reducer are as follows: molar of monomers of n(2-propenoic acid, docosyl ester):n(maleic anydride):n(styrene)=3:2:2, te reaction temperature of 80 ºC, te amount of initiator ADMVN of 0.8 wt% and te reaction time of 9 ours. 3.2 Influence of solvent amount on viscosity reducer According to te optimum reaction conditions obtained from ortogonal experiments, we fixed te monomers, and canged te proportion of monomer and solvent (metylbenzene) to obtain w(ligt oil):w(eavy oil)=0.4:1 and te amount of viscosity reducer of 2% in te total mass of tin and eavy oil. Te effects of solvent on viscosity reducer at different temperatures on TK1232 were investigated and te results can be seen in Table 4. Mass of monomer to solvent Table 4 Effect of solvent amount on viscosity of Tae TK1232 crude oil reduction at 130 Rate of viscosity reduction at 90 Rate of viscosity reduction at 50 1:1 50.0 71.3 76.6 1:2 62.5 90.3 95.5 1:3 68.7 90.3 94.0 1:4 62.5 87.9 90.7 Table 4 sows tat te weigt of monomer to solvent of oil-soluble viscosity reducer as a great effect on viscosity reduction of eavy oil. In te experiment range, wen te weigt of monomer to solvent was 1:2, te oil-soluble viscosity reducer ad te best viscosity reducing result. 3.3 Evaluation of oil-soluble viscosity reducer Under te same conditions, te viscosity reducing effects of te syntesized terpolymer and, quadripolymer viscosity reducers and commercial terpolymer on TK1232 crude oil was investigated at 90 ºC and 50 ºC, and te results are sown in Table 5. Te viscosity of TK1232 crude oil witout viscosity reducer at 90 ºC and 50 ºC is 1,416 mpa s and 12,881 mpa s, respectively.. Table 5 Te viscosity reducing effects of different copolymers on TK1232 crude oil Viscosity reducer Commercial terpolymer 1 Commercial quadripolymer 2 terpolymer quadripolymer 1 quadripolymer 2 quadripolymer 3 quadripolymer 4 Viscosity mpa s 90 ºC 50 ºC reduction, % Viscosity mpa s reduction, % 249 82.4 1511 88.3 429 69.7 3721 71.1 137 90.3 585 95.5 274 80.6 1319 89.2 515 63.6 1717 86.7 283 80.0 4293 66.7 549 61.2 6354 50.7 Table 5 sows tat te syntesized terpolymer viscosity reducer is better tan commercial viscosity reducers and te quadripolymer viscosity reducers. At 50 ºC, te viscosity of TK1232 crude oil fell from 12,881 mpa s to 585 mpa s, and te rate of viscosity reduction is 95.5%, after adding te syntesized terpolymer viscosity reducer. 3.4 IR spectra of TK1074 eavy oil wit and witout viscosity reducer IR spectra of TK1074 eavy oil wit and witout viscosity reducer are sown in Fig. 1. It can be seen tat te intensity of te absorption peak of te ydroxyl O-H decreased at 3,500 cm -1 after using viscosity reducer. Te peak of carbonyl C=O appeared at 1,736 cm -1 after using viscosity reducer. Te structure of TK1074 crude oil ad canged after using viscosity reducer. 3.5 Influence of oil-soluble viscosity reducer on oilwater interfacial tension Viscosity reducer was added to 10% TK1074 Tae model oil (te amount of viscosity reducer being 1 wt% of te model oil) and stirred to make te oil pase, and formation water was used as aqueous pase, to study te oil-water interfacial
539 Transmittance, % 120 110 100 90 80 70 60 50 40 30 20 4000 3500 3435.24 2952.99 2952.71 3000 2923.94 2853.79 2728.78 2728.16 2853.56 2923.54 2500 2000 1895.95 1849.27 1736.12 1675.89 1602.37 1604.32 1376.55 1456.95 1376.70 1461.90 1500 1261.04 1167.81 1092.16 1031.98 1031.63 1094.06 1119.05 1169.62 1250.93 1308.66 1000 864.49 807.04 745.99 723.99 865.13 811.24 767.58 742.37 723.23 697.45 692.15 483.26 432.13 500 Wave numbers, cm -1 Fig. 1 IR of TK1074 crude oil wit or witout viscosity reducer (Blue: IR of TK1974 eavy oil, red: IR of TK1074 eavy oil wit viscosity reducer) tension wit and witout viscosity reducer(see Fig. 2). Fig. 2 sows tat te interfacial tension between crude model oil and formation water system decreased dramatically wen using te viscosity reducer, indicating tat te viscosity reducer as a ig interfacial activity. Te viscosity reducer can spread from te oil pase to te oil-water interface replacing macromolecular active substances from te crude oil, so a new interfacial film is formed and te interfacial tension is greatly reduced. Interfacial tension, mn m -1 12 10 8 6 4 2 0 Model oil/formation water Model oil wit 1% viscosity reducer/formation water 0 2000 4000 6000 8000 10000 Time (t), s Fig. 2 Effect of viscosity reducer on interfacial tension between TK1074 crude model oil and formation water 3.6 Field test of te oil-soluble viscosity reducer Te field test of te developed oil-soluble viscosity reducer was carried out for two monts in well TH12510 (macine pumping well) and TH12210 (flowing well) of te second oil production plant of te Tae oilfield. Results are as follows: (1) For well TH12510, during te test, te ligt oil dilution was reduced from 0.83 to 0.49. In normal production conditions, te ligt oil needed for eavy oil dilution was decreased by 44.5%, after using oil-soluble viscosity reducer, wit an average saving rate of 21.0%, and a maximum 6.1 t/d of ligt oil was saved per day, wit an average saving amount of 4.5 t/d. (2) For well TH12210, during te test, te ligt oil dilution was reduced from 1.42 to 0.99 after using oil-soluble viscosity reducer. In normal production conditions, te ligt oil used for eavy oil dilution was decreased by 30.4%, and a maximum 12.3 t/d of ligt oil was saved per day, wit an average saving amount of 9.0 t/d. 4 Conclusions 1) Te syntetic conditions of oil-soluble viscosity reducer are as follows: under te protection of nitrogen, reaction 9, mole of raw material monomer 3:2:2, amount of initiator is 0.8%, reaction temperature is 80 ºC. In te scope of w(monomer): w(solvent)=1:1~1:4, wen w(monomer):w(solvent)=1:2, tere is te best viscosity reducing effect. 2) Te syntetic terpolymer viscosity reducer is better tan te commercial viscosity reducers and te syntesized quadripolymers. At 50 ºC, viscosity reduction rate is 95.5%. 3) Wen viscosity reducer is added, molecules of viscosity reducer interact wit te molecules of eavy oil altering te original intermolecular structure of eavy oil, weakening its ability to form ydrogen bonds wit ydroxyl or carboxyl groups, and ence te viscosity of te crude oil is reduced.
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