Energy & Fuels 1999, 13, 309-314
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Properties of Resins Extracted from Boscan Crude Oil and Their Effect on the Stability of Asphaltenes in Boscan and Hamaca Crude Oils Norman F. Carnahan* Rice University, Department of Chemical Engineering, P.O. Box 1892, Houston, Texas 77251-1892
Jean-Louis Salager, Raquel Anto´n, and Antonio Da´vila Department of Chemical Engineering, Universidad de Los Andes, Merida, Venezuela Received October 9, 1998. Revised Manuscript Received January 11, 1999
Experimental results confirm that resins isolated from Boscan crude oil have a stabilizing effect on asphaltenes in Hamaca crude oil and in Boscan crude oil. A simple experimental technique, referred to as the filter drop spreading method, was used to detect the onset of flocculation quite accurately for crude oil mixtures and for mixtures of crude oils plus additives.
Introduction Asphaltenes problems have a significant economic impact on petroleum production operations, all the way from the reservoir to the surface production facilities and transportation systems. Exploration and production implications are well-known and documented in the literature. The nature of asphaltenes in petroleum systems has been frequently discussed.1-9 The present study examines the properties of resins and natural amphiphiles extracted from a fresh atmospheric sample of Boscan crude oil and their effect on the flocculation point (asphaltenes appearance point) of asphaltenes in Boscan crude oil and in Hamaca crude oil. These results are from a preliminary study10 of petroleum colloids, including asphaltenes phenomena, focusing on the interfacial properties, characteristics, and phase behavior of the materials that coexist with and stabilize asphaltenes in crude petroleum. A principal objective of this preliminary study is to observe whether resins and/or natural amphiphiles, (1) Moschopedis, S. E.; Fryer, J. F.; Speight, J. G. Fuel 1976, 55, 227. (2) Yen, T. F.; Erdman, J. G.; Pollack, S. S. Anal. Chem. 1961, 33, 1587. (3) Selucky, M. L.; Kim, S. S.; Shinner, F.; Strausz, O. P. Am. Chem. Soc. Symp. Ser. 1981, 195, 83. (4) Ignasiak, T.; Kemp-Jones, A. V.; Strausz, O. P. J. Org. Chem. 1977, 42, 312. (5) Speight, J. G.; Moschopedis, S. E. Prepr.sAm. Chem. Soc., Div. Pet. Chem. 1979, 24 (4), 910. (6) Chemistry of Asphaltenes; Bunger, J. W., Li, N., Eds.; ACS Symposium Series 195; American Chemical Society: Washington, DC, 1981; p 195. (7) Sachanen, A. N. The Chemical Constituents of Petroleum; Reinhold Publishing Co.: New York, 1945. (8) Sheu, E. Y.; De Tar, M. M.; Storm, D. A.; DeCanio, S. J. Fuel 1992, 71, 299. (9) Petrov, A. A. Petroleum Hydrocarbons; Springer-Verlag Publishers: Berlin, 1987. (10) Davila, A. Flocculation of asphaltenes; FIRP Technical Report No. 9706, Interfacial Phenomena and Petroleum Recovery Laboratory, University of The Andes: Merida, Venezuela, 1997.
extracted from Boscan crude oil, have a beneficial impact on the stability of asphaltenes in other crude oils, as typified by Hamaca crude oil. The long-term objective of the research program is to identify naturally occurring substances that may be used as additives to stabilize asphaltenes in production operations. The notion that resins in crude oil act as stabilizing agents for asphaltenes has been reported in the literature.11-15 The concept that, in some cases, resins can be obtained from one or more crude oils and then used to stabilize asphaltenes, in other crude oils, is not universally accepted. This is partly due to (1) a limited amount of published experimental data on the effects of extracted resins and other natural amphiphiles on the stability of asphaltenes in crudes oils, in general, (2) misconceptions about the compatibility of resins and asphaltenes in crude oils from different sources, and (3) a scarcity of in-depth analytical and characterization studies of petroleum resins and asphaltenes phase behavior in petroleum systems. Research and development on the recovery, characterization, and use of naturally occurring resins and other petroleum-derived amphiphiles for use as additives to stabilize asphaltenes in crude oil production has been very limited. Murzakov et al.15 studied of the influence of petroleum resins on the colloidal stability of asphaltenes in crude oil. Gonzales and Middea16 and Chang and Fogler17 examined the use of synthetic amphiphiles as stabilizing agents for asphaltenes in petroleum. (11) Dickie, J. P.; Yen, T. F. Anal. Chem. 1967, 39, 1847. (12) Koots, J. A.; Speight, J. G. Fuel 1975, 56, 179. (13) Speight, J. G.; Moschopedis, S. E. Prepr.sAm. Chem. Soc., Div. Pet. Chem. 1981, 907-911. Speight, J. G. The Chemistry and Technology of Petroleum, 2nd ed.; Dekker: New York, 1981. (14) Paul, M.; Bhaokara, M. L. Fuel Sci. Technol. Int. 1981, S(2), 119-168. (15) Murzakov, R. M.; Sabanenkov, S. A.; Syunyaev, Z. I. Khim. Tekhnol. Topl. Masel 1980, 10, 40-41.
10.1021/ef980218v CCC: $18.00 © 1999 American Chemical Society Published on Web 02/18/1999
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Much has been written about the nature of asphaltenes and about their existence as a colloidal system in petroleum. The literature is full of information about asphaltenes from various sources, their atomic composition ratios, number of ring structures, heteroatoms, and metals, various structural models, etc.18,19 Yet despite the general recognition that asphaltenes exist as a colloidal system in petroleum, relatively little is known about the natural materials which stabilize asphaltenes in petroleum fluids, namely, the resins and other natural amphiphiles which coexist in petroleum with asphaltenes. Few studies20-22 have delved into the characterization of resins in petroleum systems. No published studies have thoroughly investigated the amphiphilic nature of such naturally occurring resins. There has been little emphasis on studies which attempt to characterize the interfacial properties of the resins in conjunction with the stability of asphaltenes in crude oil systems. Thus, we are in a situation analogous to that of a person studying emulsions, knowing about oil and about water but having only a faint clue about the nature of surfactants. Needless to say, much additional work is warranted in the study of the amphiphilic substance(s) which stabilize asphaltenes in petroleum fluids. The present study is our initial attempt to experimentally demonstrate that naturally occurring petroleum resins have interesting properties which can result in stabilization of asphaltenes in crude oils other than the oil(s) from which the resins have been obtained. Experimental Section Materials. Some characteristics and properties of the principal materials used in this study are listed below. Boscan Crude Oil. General characteristics of an atmospheric separator sample of Boscan crude oil,23,24 from the State of Zulia, Venezuela, are exhibited in Table 1. Table 3 lists the proportions of asphaltenes, resins, and natural surfactants in the Boscan and Hamaca crude oils. Hamaca Crude. Table 1 also exhibits the general characteristics of atmospheric Hamaca crude oil from well MFB 257, San Tome, State of Monagas, Venezuela.25,26 Table 2 shows representative atomic compositions of the resin and asphaltenes fractions of Hamaca crude oil. Xylene(s). Baker analyzed, MW ) 106.17, purity > 99%, density ) 0.875 g/mL, NBP ) 139.5-141 °C. n-Octane. Riedel-de Haen, MW ) 114.23, purity > 99%, density ) 0.70 g/mL, NBP ) 123-125 °C. n-Heptane. Merck, MW ) 100.21, purity > 99%, density ) 0.69 g/mL, NBP ) 98.4 °C. Experimental Method. In this section, we describe (1) the experimental methods by which the asphaltenes, resins, and natural surfactant materials were obtained from samples of (16) Gonzales, G.; Middea, A. Colloids Surf. 1991, 52, 207-217. (17) Chang, C.-L.; Fogler, H. S. SPE Manuscript No. 25185, Society of Petroleum Engineers, Dallas, Texas, March, 1993. (18) Payzant, J. D.; Lown, E. M.; Strausz, O. P. Energy Fuels 1991, 5, 445-453. (19) Yen, T. F. Chemistry of Asphaltenes; Bunger, J. W., Li, N. C., Eds.; Advances in Chemistry Series; American Chemical Society: Washington, DC, 1981; Vol. 195, pp 39-51. (20) Yen, T.-F. Encyclopedia of Polymer Science and Engineering, Index Volume, 2nd ed.; John Wiley & Sons: New York, 1990; pp 1-10. (21) Espinat, D.; Ravey, J. C. Colloidal structure of asphaltene solutions and heavy oil fractions by small-angle neutron and X-ray scattering; SPE Manuscript No. 25187; Society of Petroleum Engineers: Dallas, Texas, 1993. (22) Pfeiffer, J. P.; Saal, R. N. J. J. Phys. Chem. 1940, 44, pp 139149. Pfeiffer, J. P. The Properties of Asphaltic Bitumen; Elsevier: Amsterdam, 1950.
Carnahan et al. Table 1. Characteristic Properties of Boscan and Hamaca Crude Oils property
Boscan
API gravity specific gravity flash point (°F) pour point (°F) mercaptans (mg/L) acid number (mg of KOH/g) aromatics (wt %) sulfur (wt %) nitrogen (mg/L) vanadium (µg/L) (neutron activation) sodium (mg/L) nickel (µg/g) kinematic visocosity at 85 °F (cSt) kinematic visocosity at 140 °F (cSt) kinematic visocosity at 180 °F (cSt) water (wt %) atmospheric residue at 590 °F (wt %)
Hamaca
10.1
8.5-10 1.0107-0.9993 235-248 60-75 54.67-54.97 1.58-2.67 37-39.8 5.66 2.8-3.7 6013-6395 6013-6395 1220 364 + 16 110 150 81-116 50 × 103 1832 2.25-6.20 × 103 800 1.70-3.34 × 102 0.45 86.7
Table 2. Atomic Composition (mass %) of Resins and Asphaltenes from Hamaca Crude Oil substance
C
H
O
N
S
resins asphaltenes
82.0 83.4
9.4 7.6
3.4 2.7
1.3 1.8
3.9 4.5
Table 3. Mass Percentages of Asphaltenes, Resins, Natural Surfactants, and Maltenes in Boscan and Hamaca Crude Oils component
Boscan
Hamaca
asphaltenes (n-C7) resins resin I resin II natural surfactant in crude natural surfactant in maltenes maltenes
19.6 25.3 4.4 25.3 1.7 1.3 80.4
18.2 20.7 5.6 20.7 1.6 1.2 83.8
Figure 1. Schematic procedure used for obtaining resin I material from Boscan or Hamaca crude oil samples. Boscan and Hamaca crude oils and (2) the experimental methods used to measure and observe the effect of those materials on the stability of asphaltenes in Boscan and Hamaca crude oils. The filter drop spreading method27 is also described. The availability of large quantities of Boscan crude oil and Hamaca crude oil made it possible to perform multiple operations to obtain necessary quantities of the asphaltenes, resin I, resin II, and natural surfactant materials described herein. Resin I was obtained via Soxhlet extraction using a sample portion of the unwashed initial asphaltenes precipitate, as shown in Figure 1, whereas, resin II was obtained from the combined liquids from the asphaltene precipitation and washing processes via adsorption onto silica gel, as shown in Figure 2.
Resins Extracted from Boscan Crude Oil
Figure 2. Schematic procedure used for obtaining resin II material from Boscan or Hamaca crude oil samples. Asphaltenes. Asphaltenes were precipitated from 100 g samples of Boscan and Hamaca crude oils by addition of a 20:1 volume ratio of n-heptane. The mixture was allowed to rest at ambient temperature for 24 h and then filtered to recover the initial asphaltenes residue. The initial asphaltenes residue was washed with approximately 500 mL of n-heptane, until the liquid passing from the filter was very light yellow in color. The objective of this washing procedure was to remove additional resins which may have been adsorbed onto the precipitated asphaltenes or may have been occluded in the initial asphaltenes precipitate. The washed residue was maintained at 80 °C in an inert atmosphere, until the weight of residue remained constant. The final weight is reported in terms of weight percent of asphaltenes in the crude oil. Resin I. The unwashed initial asphaltenes residue that was precipitated from Boscan and Hamaca crude oils was processed by Soxhlet extraction, using n-heptane as the liquid. The Soxhlet liquid was then vacuum distilled, leaving resin I as the residue. The recovered material was dried, weighed, and reported on the basis of weight percent of resin I in the crude oil sample. Resin II. Resin II was obtained from the deasphalted crude oil + n-heptane filtrate + n-heptane wash liquid by adsorption onto activated silica gel. Resin II is soluble in n-heptane. The adsorbed material was recovered by washing the silica gel with a 90:10 (volumetric) mixture of xylenes and methanol. The xylene-methanol wash mixture was then vacuum distilled to concentrate resin II. The residue material was dried, weighed and reported as weight percentage of resin II in the sample of Boscan crude oil or Hamaca crude oil. Natural Surfactant. Natural surfactants, in this study, were recovered from deasphalted Boscan crude oil and also from deasphalted Hamaca crude oil. Deasphalted oil was combined with a 25:75 (volumetric) mixture of xylenes and n-heptane in order to dissolve the maltenes. To this mixture was added small portions of distilled water, with vigorous agitation, forming a water-in-oil emulsion, until the total liquid content was approximately 70% water. The entire mixture was centrifuged and washed with the 25:75 xylenes:n-heptane solvent to remove free oil that was not emulsified. Free oil, plus solvent, was drained from the container, leaving the emulsion phase. The emulsion was broken by addition of an excess of the 90:10 (volumetric) mixture of xylenes and methanol and maintaining the liquid at 40 °C for 4 h. The mixture of xylenes, methanol, and natural surfactants was recovered by decantation, and then it was vacuum distilled to recover the natural surfactants, which were dried, weighed, and reported as weight percentage in the crude oil.
Energy & Fuels, Vol. 13, No. 2, 1999 311 Filter Drop Spreading Method. The filter drop spreading method was adapted and developed as part of a study,27 by J. M. Fourest, of asphaltenes precipitation from Hamaca crude oil. The method allows accurate, rapid determination of the flocculation point of the asphaltenes, measured in terms of the proportion of n-alkane added to the crude oil. This test consists of preparing a sample of crude oil(s), mixed with a fixed proportion of xylenes, to which an n-alkane is added in small quantities. A drop of the crude oil + xylenes + n-alkane mixture is placed in the center of the filter paper. The liquid drop spreads in a circular pattern. The procedure is performed, in this study, at ambient conditions, in which the temperature was about 18.9 °C. If the entire pattern is uniform in color and color density, this signifies the absence of flocculation. When asphaltenes flocculate, the pattern exhibits a darker center ring with a lighter color outer ring. By adding n-alkane diluent in small steps, one can detect the concentration above which flocculation commences. The volume percentage of n-alkane, at which flocculation commences, is reported as the flocculation point of the crude oil. As a test of the filter drop spreading method, a series of 10 measurements was performed using the same sample, consisting of approximately 5 g of Hamaca crude oil diluted with xylene to a concentration of 40% in the mixture. These 10 specimens were mixed with small additional volumes of n-octane, until flocculation was observed. Measurements determined that flocculation in the crude oil + xylene mixture occurred in the range between 62.28% and 62.32% n-octane in the mixture, with a variation of (0.04%. Therefore, the filter drop spreading method is a useful technique for our purposes, as it permits detection of small changes in the tendency of the crude oil sample to precipitate asphaltenes. To achieve sufficiently high precision for each flocculation point, we used three equal portions of the same sample and three measurement steps. The first step was a rough determination of the range of n-octane concentration in which the flocculation point occurs, by addition of n-octane in 2 mL increments, until flocculation was observed. The second step involved rapid titration with an n-octane volume just below the range of n-octane concentration in which the flocculation point occurred step one and then slow titration with n-octane in 0.2 mL in increments, until the flocculation point was observed with higher precision. The third step was used to confirm the flocculation point found in the second step. The flocculation point proved to be a useful measure of asphaltenes stability and of the capacity of crude oils to inhibit flocculation of asphaltenes at a fixed composition. The filter drop spreading method is a useful, sensitive, and simple test that can be performed in the laboratory or at field production locations.
Results Flocculation Point for Mixtures of Hamaca and Boscan Crude Oils. Boscan crude oil is believed to contain resins and natural amphiphiles in excess of the proportion required to stabilize the asphaltenes in Boscan crude oil. Boscan crude oil is recognized as being (23) Aquino, P. Demetallization and desulfurization of deasphalted oils of heavy Venezuelan crudes. Rev. Tec. INTEVEP 1981, 1 (1), 3-8. (24) Lichaa, P. Electrical and other effects related to the formation and prevention of asphaltenes depositions problem in Venezuelan crudes; SPE Manuscript No. 5304; Society of Petroleum Engineers: Dallax, Texas, 1975. (25) Layrisse, I.; Rivas, H.; Acevedo, S.; Medina, R.; Sanchez, U. Rev. Tec. INTEVEP 1984, 4 (1), 3-18. (26) Acevedo, S.; Mendez, B.; Rojas, A.; Layrisse, I. Fuel 1985, 64, 1741-1748. (27) Fourest, J. M. Study of asphaltenes precipitation from Hamaca crude oil; Technical Report of FIRP-Elf Aquitane Project; Interfacial Phenomena and Petroleum Recovery Laboratory, University of The Andes: Merida, Venezuela, 1995.
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Figure 3. Flocculation point for mixtures of Hamaca and Boscan crude oils.
Carnahan et al.
Figure 5. Effect of xylenes on the flocculation point of Hamaca crude.
Figure 4. Effect of adding resin II on the flocculation point of Hamaca crude.
Figure 6. Effect of resin II on the flocculation point of mixtures of resin II and asphaltenes dispersed in high concentrations of xylene.
one of the more stable crude oils in Venezuela, from the point of view of asphaltenes problems in production. It is interesting to observe if the addition of Boscan resins can enhance the stability of asphaltenes in the Hamaca crude oil that presents considerable asphaltenes-related problems during production. To study this effect, the flocculation point was determined for Boscan crude oil, for Hamaca crude oil, and for mixtures of Boscan and Hamaca crude oils. Figure 3 shows that the flocculation point of the very stable Boscan crude oil is higher than that of problematic Hamaca crude oil. The flocculation points for mixtures of Boscan and Hamaca crude oils are observed to be higher than the linear average of the individual flocculation points of Hamaca crude oil and Boscan crude oil. This is preliminary evidence that Boscan crude oil contains substances that not only act to disperse its own asphaltenes, but also can effectively disperse the asphaltenes of the Hamaca crude oil. Effect of Resin II on the Flocculation Point of Hamaca Crude. Figure 4 shows the effect of resin II on the flocculation point of Hamaca crude oil. Resin II was extracted from Hamaca crude oil and Boscan crude oil. Figure 4 also shows the effect of contact time. In this experiment, the percentage of xylene is relative to the mixture of xylene + resin II + Hamaca. The flocculation point is reported as percentage n-octane with respect to the total mixture, that is, crude oil, resin II, xylene, and n-octane. As shown, resin II extracted from both crude oils exhibits a similar effect on the flocculation point of Hamaca crude, although resin II from Boscan appears more effective. The floc-
culation point increases monotonically and linearly in proportion to the amount of resin II added to the mixture. This infers that resin II acts as a stabilizer of asphaltenes in Hamaca crude oil. Increasing the resins/asphaltenes ratio seems to result in greater dispersion of asphaltenes in the crude oil. Addition of resin II noticeably inhibits the flocculation threshold of asphaltenes in Hamaca crude oil. Furthermore, there is an immediate effect, which improves with time, as the resins interact with resinasphaltenes colloidal particles. Thus, some kinetic process appears active. One could infer that the additional resins aggregate with existing colloidal particles, resulting in more stable colloidal particles. Effect of Xylene Concentration on the Flocculation Point of Hamaca. Figure 5 shows the variation of the flocculation point for the mixture of Hamaca and xylenes as a function of the proportion of xylenes in the mixture. In this experiment, the percentage of n-octane is reported on the basis of the total solution, i.e., Hamaca crude, xylenes, and n-octane. The flocculation point is observed to be almost constant over a wide range of xylenes concentration. The resulting experimental uncertainty, by using approximately 40% xylenes concentration in the crude oil + xylenes mixture, is assumed to be minimal. Effect of Resin II on the Flocculation of Asphaltenes Dispersed in Xylenes. Figure 6 shows the effect of the resin/asphaltenes ratio on the flocculation point of mixtures of asphaltenes and resin II dispersed in xylenes. The contact time for the mixtures of xylenes, asphaltenes, and resin II was 12 h, after which the
Resins Extracted from Boscan Crude Oil
Energy & Fuels, Vol. 13, No. 2, 1999 313
Figure 7. Effect of the resin II/asphaltenes ratio on the flocculation point of asphaltenes.
Figure 9. Effect of natural surfactant derived from Boscan crude oil on the flocculation point of Hamaca crude oil.
Figure 8. Effect of resins I and II on the flocculation point of Hamaca crude oil in a mixture consisting of 60% crude oil and 40% xylenes.
Effect of Natural Surfactants on the Flocculation Point of Hamaca Crude Oil. Figure 9 shows the negative effect that the natural surfactants have on asphaltenes stability in Hamaca crude oil. Recall that the natural surfactants, in this study, are isolated from the deasphalted crude oil by (1) adsorption at an oilwater interface, (2) formation of an emulsion, and (3) subsequent breaking of the emulsion to recover the natural surfactant. The natural surfactants recovered in this manner, from deasphalted oil, do not contain asphaltenes. These natural surfactants, isolated from deasphalted oil (maltenes) via aqueous emulsion formation, destabilize asphaltenes in Hamaca crude oil. The effect increases with time, indicating that the natural surfactant material slowly interacts negatively with the colloidal system.
flocculation point was determined for each mixture. Asphaltenes were isolated from Hamaca crude, using n-heptane. Resin I was subsequently removed from the asphaltenes via the Soxhlet method. Because asphaltenes are difficult to disperse at less than 70% xylenes, these flocculation points were determined at 90% xylenes concentration. The flocculation point increases in proportion to the resin/asphaltenes ratio in the mixtures. The flocculation points range from about 41% to 43% up to almost the value observed for Hamaca crude oil at resin/asphaltenes ratios greater than 90:10, although the asphaltenes in these mixtures have been isolated from the Hamaca crude oil. Figure 7 shows the effect of the resin II/asphaltenes ratio on the flocculation point of mixtures of resin II (derived from Boscan and Hamaca crude oils) and Hamaca asphaltenes dispersed in xylenes. The stabilizing effect of an increased resin/asphaltenes ratio is evident. Moreover, resin II from either Boscan or Hamaca crude oil is observed to have a stabilizing effect on Hamaca asphaltenes. Effect of Resin I and Resin II on the Flocculation Point of Hamaca Crude Oil. Figure 8 shows the initial effect of adding resin I or resin II to a mixture of Hamaca crude oil and xylenes. Resin I and resin II, derived from Boscan or Hamaca crude oils, have a favorable and prompt effect on stabilizing asphaltenes in Hamaca crude oil.
Discussion All of our experimental results confirm that addition of resin I or resin II, from Boscan crude oil or from Hamaca crude oil, enhances the stability of asphaltenes in Hamaca crude oil. There appears to be a rough correlation between the polarity of the material added and its stabilizing effect on asphaltenes in crude oil. The most polar and hydrophilic material, the natural surfactant, actually destabilizes asphaltenes in crude oil. There also appears to be some correlation between the polarity of the added substance and its relative hydrophile-lipophile balance (HLB) index, insofar as interaction of such additives with asphaltenes-containing colloidal particles and with the asphaltenes-free oil phase. Resin I has a positive effect on the asphaltenes stability; however, the effect is less than the observed for resin II. Resin I consists of a material which may have been occluded and bound to the initially precipitated asphaltenes material, as well as some lower molecular weight asphaltenes which were solubilized in the Soxhlet procedure. Resin II includes resin I plus additional resin adsorbed by the silica gel from the asphaltenes filtrate and the n-heptane wash liquid. Boscan resins I and II are found to be more effective than Hamaca resins I and II as asphaltenes stabilizers in Hamaca crude oil. Because resin I and resin II are isolated using the same methods for each crude oil, the reason Boscan resins are more effective than the
314 Energy & Fuels, Vol. 13, No. 2, 1999
Hamaca resins is yet unresolved. One might expect that the addition of Hamaca resins to Hamaca crude oil would be more compatible. This study has used only two crude oils. Perhaps the results would be different in a more general study. Nonetheless, we believe that these results would be confirmed by a more extensive study of the underlying chemistry and interfacial phenomena. This study has consistently used the observed onset of flocculation as the measure of the effectiveness of asphaltenes stability in crude oil. Murzakov et al.15 reported results based on the quantity of asphaltenes precipitated, as observed by gravimetric sedimentation analysis. They reported significant enhancement of asphaltenes stability for resin concentrations between 2% and 8%. Our measurements were performed at laboratory ambient conditions at the University of The Andes, Merida, Venezuela. The local altitude is 1603.21 m above mean sea level. The average temperature is about 18.9 °C. In a practical sense, addition of resins to crude oil ought to be done at conditions corresponding to the reservoir temperature and pressure. Under such “native environment” conditions, we expect the interaction between resins and the colloidal systems to be greater. Conclusions Resins from Boscan crude oil and from Hamaca crude oil can stabilize asphaltenes in Hamaca crude oil.
Carnahan et al.
Boscan resins are more effective than Hamaca resins as asphaltenes stabilizers for Hamaca crude oil. The filter drop spreading method is a useful technique for detecting the onset of flocculation of asphaltenes in crude oil and in mixtures of crude oils and additives. Additional experimental work is needed in order to properly define the mechanism(s) of asphaltenes stabilization by various resins and their fractions in petroleum systems. Thorough analyses and characterization of chemical and interfacial properties of petroleum resins and other natural amphiphiles is warranted as a means to better understand the physicochemical aspects of their interaction with asphaltenes and the continuous crude oil phase. A judicious choice of oil mixtures, in commingling situations, may not only avoid compatibility problems, but can lead to enhanced stability of asphaltenes in crude oil mixtures. Acknowledgment. The authors express their gratitude to the Universidad de Los Andes, for the facilities to perform the experimental study, to Maraven, S.A. (an affiliate of Petroleos de Venezuela, S.A.), for their assistance and cooperation by providing a generous supply of Boscan crude oil, and to Rice University. EF980218V
