Waxy crude oil

The crystallization of waxes at lower temperatures causes reduced liquidity of waxy crude oils, which considerably hampers the transportation of crude oils through long distance pipelines. Taking into consideration all of the economic aspects, additive treatment, which depresses the pour point and improves the... 

M. N. Sunil Kumar. Review on polymeric and copolymeric pour point depressants for waxy crude oils and studies on bombay high crude oil. Quart J Tech Pap (Inst Petrol), pages 47-71, October-December 1989. 

Some crude oils are low in sulphur and waxy. Crude oil of this nature is common in South Asia and is processed in large simple refineries. They produce a fuel oil which is referred to as low sulphur residual fuel oil (LSWR) for export. LSWR generally sells at a premium to fuel oil, but the price differential is seasonal with a major market being... 

A hydrophobically modified polybetaine proved to be an efficient pour point depressant (PPD), to inhibit the deposition of wax, and to improve the viscosity of waxy crude oil from the Kumkol-Akshabulak oil field (western Kazakhstan) [282]. The inhibition of wax deposits in the presence of the hydrophobic polybetaine was interpreted in terms of its interference with the wax crystalhzation process, due to the formation of inverse micellar structures. While the zwitterionic parts on the polymer backbone stabilize the... 

The best activity was observed for PCMEDDAC dissolved in n-hexane. Initial waxy crude oil behaves hke a viscoplastic fluid. Doped by PCMEDDAC, waxy oil approaches a Newtonian liquid, and the shear stress decreases considerably due to the modification of the paraffin crystals by the hydropho-bized macromolecules, hi oily environments, PCMEDDAC forms micelles consisting of a hydrophihc core (made of the betaine groups) and a hydrophobic corona (made of the dodecyl groups). The PPD mechanism of PCMEDDAC with respect to waxy crude oil suggests the adsorption of definite fractions of paraffin molecules on the surface of micelles and further retardation of agglomeration. 

Although the pour point test is still included in many specifications, it is not designated for high-boiling fuel oil (ASTM D 396). In fact, although the failure to flow at the pour point normally is attributed to the separation of wax from the fuel oil (in the case of waxy crude oil precursors), it also can be due to the effect of the viscosity of the fuel oil (in the case of naphthenic crude oil precursors). In addition, the pour point of fuel oil may be influenced by the previous thermal history of the fuel oil. Thus the usefulness of the pour point test in relation to fuel oil, especially residual fuel oil, may be open to question. 

The occurrence of HMWHCs in crude oils has typically been determined by simulated distillation but the poor chromatographic resolution associated with this approach has been a limiting factor in understanding the complexity of the HMWHC fraction (Trestianu et al. 1985 Thomson Rynaski 1992 Neer Deo 1995 Durand et al. 1998). Routine analyses of waxy crude oils by HTGC have revealed that HMWHCs are composed of complex mixtures of alkyl-cycloalkanes, methylbranched alkanes, and alkyl-aromatic hydrocarbons, and may represent a significant fraction of the whole oil (Hsieh Philp 2001). 

To date, we have identified homologous series of monomethylalkanes, n-alkylcyclohexanes, methyl-M-alkylcyclohexanes, -alkylcyclopen-tanes, n-alkylbenzenes, -alkyltoluenes and n-alkylxylenes, in waxy crude oils. Each of these compounds has unique physical properties, and will affect the overall behaviour of an oil (e.g. melting point properties and wax crystal arrangement). Identification of these compounds will improve any efforts to model or predict the wax deposition potential of oils. As we come to know the exact structure of constituents in the HMWHC fraction, we will be able to gain better insights into the origin and mechanisms for the formation of HMWHCs in crude oils and source rocks. 

AjffiNKA, J. A. Ikoku, C. U. 1990. Waxy crude oil handling in Nigeria practices, problems, and prospects. Energy Sources, 12, 463-478. 

TR Sifferman. Flow properties of difficult to handle waxy crude oils. J Petrol Technol (Aug.) 1047—1050, 1979. 

Waxy crude oils, such as those found in the North Sea (20), would not produce a smooth decline in viscosity with increases in temperature. Wax as fine particles would contribute to a high viscosity and when heated between 50°C and 65°C would melt or solubi-lize in low-molecular-weight components, produeing a more homogeneous fluid (17, 18). The properties of erude oils and bitumen are listed in Table 1. 

T Stroem-Kristiansen, ALewis, PS Daling, JN Hokstad, I Singsaas. Weathering and dispersion of naphthenic, ash-phaltenic, waxy crude oils. Proceedings of Intemational Oil Spill Conference, Fort Lauderdale, FL, 1997, pp 631—... 

Chanda, D., Sarmah, A., Borthakur, A. (1998). Combined effect of asphaltenes and flow improvers on the rheological behaviour of Indian waxy crude oil. Fuel. 77 (11) 1163-1167. 

Kane, M., Djabourov, M., Voile, J-L., Lechaire, J-P., and Frebourg, G. (2003). Morphology of paraffin crystals in waxy crude oils cooled in quiescent conditions and imder flow. 

Morphology of paraffin crystals in waxy crude oils cooled in quiescent conditions and xmder... 

Wang, B., and Dong, L.D. (1995). Paraffin characteristics of waxy crude oils in China and the methods of paraffin removal and inhibition. Paper SPE 29954, SPE International Meeting on Petroleum Engineering, Beijing, China. November 14-17, 33-48. 

Precipitation and gelation of long-chain paraffins in waxy crude oils hinders their fiow and hence their recovery and processing. Flow characteristics can be im-... 

Diblock copolymers (e.g., low molecular weight polyethylene-poly(ethyle-nepropylene)) are added to waxy crude oils to reduce their tendency to solidify on the walls of pipes, which ultimately results in blocking the flow. In small quantities, these copol5mers co-crystallize with crude oil, forming a weaker gel which... 

Note 2—It has been observed that for some waxy crude oils, temperatures of 7I C(I60 F) or higher may be required to melt the wax crystals completely so that they are not measured as sediment. If temperatures higher than 60 C (140 F) are necessary to eliminate this problem, they may be used with the consent of the parties involved. If water saturation of the solvent is required, it must be done at the same temperature. 

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