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Chapter 7 | Crude Oils
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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. They have been characterized as “possibly the most complicated chemical mixture known to science. A single heavy petroleum sample, for example, may contain more than 30,000 chemical substances.” Not only is the composition of crude oil extremely complex, it is also highly variable from field-to-field, and even within a given field it is likely to exhibit differences in quality from one well to another. Physical and chemical characterization of this complex mixture is complicated by the fact that crude oils are not pure solutions, but usually contain colloidally-suspended components, dispersed solids, and both free and emulsified water. Two different analytical schemes are commonly used in analysis of crude oils: namely, an inspection assay and a comprehensive assay. Inspection assays involve determination of a few key whole crude oil properties such as API gravity, sulfur content, and pour point. The comprehensive assay, which involves fractional distillation of samples, is complex, costly, and time-consuming. Few, however, of the test methods used in analysis of crude oils are specific to that purpose. With the growing diversity of crude oil streams resulting from greater production of bitumen-derived streams and light tight oils, the need for more comprehensive analytical schemes is also increasing. This chapter provides an overview of the methods commonly used in performing inspection and comprehensive analyses, the importance of a representative sample, referee test methods, compatibility issues, and future needs in analytical methodology.
crude oils, analysis, sampling, compatibility, test methods
Giles, Harry N.
PetroStorTech LLC, Arlington, VA