Standard Guide for Elemental Analysis of Crude Oil

Abstract

4.1 This guide summarizes the test methods used in the elemental analysis of crude oils. Additional information on the significance and use of the test methods quoted in this guide can be found under discussion of individual test methods in Sections 9 through 16. 4.2 Crude oils are highly complex hydrocarbons also containing some organometallic compounds, inorganic sediment, and water. Nearly 600 individual hydrocarbons, over 200 separate sulfur compounds, and about 40 trace elements have been found in crude oils (1).6 Generally, sulfur and nitrogen are the two most abundant elements found in crude oils except for carbon and hydrogen. Most other inorganic elements are present at trace levels (mg/kg). Sulfur, nitrogen, vanadium, nickel, and iron are the most frequently determined elements in the crude oils. Ratios such as vanadium to vanadium + nickel, and iron to vanadium are suggested as being useful for oil type characterizations. Since organometallic compounds are concentrated in the heavy ends of petroleum, transition element concentrations and ratios can serve as excellent oil-oil correlation parameters. Generally, vanadium and nickel content increases with asphaltic content of crude oil (API gravity is an indicator). Lighter crude oils contain lesser amounts of metals (2, 3). 4.3 Metal complexes called porphyrins are a major component of metallic compounds in crude oils. The principal porphyrin complexes are Ni+2 and VO+2 compounds. There are also other non-porphyrin complexes and other metallic compounds present in crude oils (4, 5). 4.4 Some typical literature citations in this area are included in the reference section at the end of this guide.