Published: Jan 2010
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CRUDE OILS ARE A HIGHLY COMPLEX COMBINAtion of hydrocarbons; heterocyclic compounds of nitrogen, oxygen, and sulfur; organometallic compounds; inorganic sediment; and water. Approximately 600 different hydrocarbons have been positively identified in crude oil, and it is likely that thousands of compounds occur, many of which probably will never be identified. In a study sponsored by the American Petroleum Institute (API), nearly 300 individual hydrocarbons were identified in Ponca City, Oklahoma, crude oil [1,2]. Some 200 individual sulfur compounds were identified in a 20-year systematic study of four crude oils . Not only is the composition of crude oil highly complex, it is also highly variable from field to field, and even within a given field, it is likely to exhibit inhomogeneity from reservoir to reservoir. Physical and chemical characterization of this complex mixture is further complicated for the analyst by the fact that crude oils are not pure solutions but commonly contain colloidally suspended components, dispersed solids, and emulsified water. Compared to refined products such as gasoline and aviation turbine fuel, there is relatively little in the literature on the analysis and characterization of crude oils. Indeed, for many years, there were relatively few ASTM methods specific to crude oils, although a number of ASTM methods had been adapted for their analysis. This situation may have resulted, at least in part, from the historical tendency of refinery chemists to independently develop or modify analytical methods specific to their needs and, subsequently, for the methods to become company proprietary. In recent years, the unique problems associated with sampling and analysis of crude oils have received more attention, and more methods for determining selected constituents and characteristics of crude oils have been standardized. A series of articles [4–9] illustrate the diversity of crude oil assay practices employed by major refiners in the United States and Austria. The dissimilarity of published results  and as provided by a number of companies on their Web sites  is a reflection of this independent development of analytical schemes, even though standardized approaches to crude oil analysis have been published [12–15]. Despite the complexity of crude oil composition and the diversity of analytical methodology, probably more crude oil analyses are routinely performed on a daily basis using inherently similar methods than are analyses on any single refined petroleum product except, possibly, gasoline.
Giles, Harry N.
PetroStorTech LLC, Arlington, VA