Composition of crude oil

Chapter 1. COMPOSITION OF CRUDE OILS AND PETROLEUM PPODUCTS... 

Chapter 1. Composition of Crude Oils and Petroleum Products... 

Chapter 1. COMPOSITION Of CRUDE OILS AND PETROLEUM PRODUCTS 7... 

Crude oil is a mixture of many different hydrocarbons and small amounts of impurities. The composition of crude oil can vary significantly depending on its source. Petroleum refineries are a complex system of multiple operations and the operations used at a given refinery depend upon the properties of the crude oil to be refined and the desired products. For these reasons, no two refineries are alike. Portions of the outputs from some processes are re-fed back into the same process, fed to new processes, fed back to a previous process, or blended with other outputs to form finished products. The major unit operations typically involved at petroleum refineries are described briefly below. In addition to those listed below, there are also many special purpose processes that cannot be... 

Modifications in the Composition of Crude Oils During In Situ Combustion... 

The depositional environment of the oil source rocks, its thermal evolution, and secondary alteration processes are the most important factors, which determined the composition of crude oil. 

The ternary diagram in Figure 4 shows the composition of crude oil samples based on the content of normal plus isoalkenes (parafliins), cycloalkenes (naphtenes), and aromatic hydrocarbons plus polar, heteroatomic compounds (NSO). 

Any composition of crude oil depends on the combination of various factors. Among the environmental factors, those that influence the nature of the organic matter in the source rock and its mineral composition are of primary significance. 

The composition of crude oil may vary with the location and age of an oil field, and may even be depth dependent within an individual well or reservoir. Crudes are commonly classified according to their respective distillation residue, which reflects the relative contents of three basic hydrocarbon structural types paraffins, naphthenes, and aromatics. About 85% of all crude oils can be classified as either asphalt based, paraffin based, or mixed based. Asphalt-based crudes contain little paraffin wax and an asphaltic residue (predominantly condensed aromatics). Sulfur, oxygen, and nitrogen contents are often relatively higher in asphalt-based crude in comparison with paraffin-based crudes, which contain little to no asphaltic materials. Mixed-based crude contains considerable amounts of both wax and asphalt. Representative crude oils and their respective composition in respect to paraffins, naphthenes, and aromatics are shown in Figure 4.1. 

Sofer, Z., 1984, Stable Carbon Isotope Composition of Crude Oils Application to Source Depositional Environments and Petroleum Alternation American Association of Petroleum Geologists Bulletin, Vol. 68, pp. 31 49. 

Combined stable isotope analysis ( C, D, N, has been used successfully in petroleum exploration (Stahl 1977 Schoell 1984 Sofer 1984). The isotopic composition of crude oil is mainly determined by the isotopic composition of its source material, more specifically, the type of kerogen and the sedimentary environment in which it has been formed and by its degree of thermal alteration (Tang et al. 2005). Other secondary effects like biodegradation, water washing, and migration distances appear to have only minor effects on its isotopic composition. 

Asphalt Roofing Components. Asphalt (qv) is a unique building material which occurs both naturally and as a by-product of crude-oil refining. Because the chemical composition of crude oils differs from source to source, the physical properties of asphalts derived from various crudes also differ. However, these properties can be tailored by further processing to fit the application for which the asphalt will be used. Softening point, ductility, flash point, and viscosity—temperature relationship are only a few of the asphalt properties that are important in the fabrication of roofing products. 

Liquid chromatography (also called adsorption chromatography) has helped to characterize the group composition of crude oils and hydrocarbon products since the beginning of this century. The type and relative amount of certain hydrocarbon classes in the matrix can have a profound effect on the quality and performance of the hydrocarbon product. The fluorescent indicator adsorption (FIA) method (ASTM D-1319) has been used to measure the paraffinic, olefinic, and aromatic content of gasoline, jet fuel, and liquid products in general (Suatoni and Garber, 1975 Miller et al., 1983 Norris and Rawdon, 1984). 

The term physical composition (or bulk composition) refers to the composition of crude oil as determined by various physical techniques. For example, the separation of petroleum using solvents and adsorbents (Altgelt and Boduszynski, 1994 Speight, 1999) into various bulk fractions (Figure 3-8) determines the physical composition of crude oil. However, in many instances, the physical composition may not be equivalent to the chemical composition. These methods of separation are not always related to chemical properties and the terminology applied to the resulting fractions is often a terminology of convenience. 

VGC (viscosity-gravity constant) an index of the chemical composition of crude oil defined by the general relation between specific gravity, sg, at 60°F and Saybolt Universal viscosity, SUV, at 100°F ... 

These examples illustrate recent interest in investigating the potential of sulfur compound distributions for improving our understanding of geologic influences in determining variations in composition of crude oils with relation to source and evolution history. 

Clayton J. L. (1993) Composition of crude oils generated from coals and coaly organic matter in shales. In Hydrocarbons from Coal, AAPG Studies in Geology 38 (eds. B. E. Law and D. D. Rice), American Association of Petroleum Geologists, Tulsa, OK, pp. 185-201. 

Andrusevich V. E., Engel M. H., Zumberge J. E., and Brothers L. A. (1998) Secular, episodic changes in stable isotopic composition of crude oils. Chem. Geol. 152, 59-72. 

Sofer Z. (1984) Stable carbon isotope compositions of crude oils application to sourc e depositional environments and petroleum alteration. Am. Assoc. Petrol. Geol. Bull. 68(1),... 

The composition of crude oils differs in different parts of the world as does the type of metal present and concentration. The different metal contents can be useful for identification of the source of oil and also help in determining those responsible as part of forensic and environment pollution investigations. Wear metals in lubricating oil are also monitored to provide early detection and correction of major problems in the various machine parts. 

This profile covers total petroleum hydrocarbons (TPH), which is defined as the measurable amount of petroleum-based hydrocarbon in an environmental medium (Chapter 2). TPH is measured as the total quantity of hydrocarbons without identification of individual constituents. Sources of TPH contamination in the environment range from crude oil, to fuels such as gasoline and kerosene, to solvents, to mineral-based crankcase oil and mineral-based hydraulic fluids. These products contain not only a large number and variety of petroleum hydrocarbons, but also other chemicals that, strictly speaking, are not the subject of this profile, such as non-hydrocarbon additives and contaminants. The TPH issue is further complicated by the number of petroleum-derived hydrocarbons that have been identified—more than 250—and the variability in composition of crude oils and petroleum products (see Section 3.2 and Appendices D and E for details). 

It is commonly thought that crude oil from conventional oil wells is quite similar in appearance and composition, regardless of the source. This is not so. The physical characteristics and the composition of crude oils vary widely with the location of the oil field and the stage of production (new or mature). 

TABLE 18.1 I Percent Composition of Crude Oil after 308 Days in Contact with Soil Plus Various Additives, Swan Hills, Alberta"... 

---