Classification Approach to Assay of Crude Oils with Different Physicochemical Properties and Quality Parameters

Abstract

An approach to crude oil assay based on the consistent application of two heterogeneous classifications of oils is proposed: according to the quality index and physicochemical parameters. The methodological issues of the classification approach to oil analysis, implemented in the form of a two-stage procedure, are described. The approach is illustrated by an example of analysis of the characteristics features of different types of tight oils in Russia. The analysis used data from 25.190 oil samples with abnormal properties and 10 500 oil samples with complex modes of occurrence. At the first stage, the analysis has been carried out using the classification of tight oils according to the quality index; as a result, the oils were divided into three homogeneous classes: low, medium, and high quality oils. At the second stage of the analysis, the classification of oils by physicochemical characteristics has been used, taking into account the density; viscosity; sulfur, resin, asphaltene, wax, vanadium, nickel, and light end contents; gas saturation of oil; etc. The analysis made it possible to establish the characteristic features of the physicochemical properties of tight oils belonging to different quality classes.

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Classification of oils by physicochemical properties

Property	Oil class		Limits of change in classification intervals
Density, g/cm3	Very light		Less than 0.80
	Light		0.80–0.84
	With medium density		0.84–0.88
	Heavy	With increased density	0.88–0.92
		Extraheavy	0.92–0.96
		Bituminous	More than 0.96
Viscosity at 20°С, mm2/s	Low viscosity		Less than 10
	Medium viscosity		10–35
	Viscous	With increased viscosity	35–100
		Highly viscous	100–500
		Extra viscous	More than 500
Sulfur content, wt %	Low sulfur		Less than 0.5
	Medium sulfur		0.5–1
	Sour		1–3
	High sulfur		More than 3
Resin content, wt %	Slightly resinous		Less than 8
	Medium resinous		8–13
	Resinous	Moderately resinous	13–20
		Highly resinous	20–30
		Ultrahigh resin	More than 30
Asphaltene content, wt %	Low asphaltenic		Less than 3
	Medium asphaltenic		3 –10
	Highly asphaltenic		More than 10
Wax content, wt %	Low wax		Less than 1.5
	Medium wax		1.5–6
	Waxy	Moderately waxy	6– 10
		Highly waxy	10–20
		Ultrahigh wax	More than 20
Amount of IBP–200°C fraction, wt %	low content		Less than 15
	medium content		15 –30
	high content		More than 30
Amount of IBP–300°C fraction, wt %	low content		Less than 30
	medium content		30–50
	high content		More than 50
Amount of IBP–350°C fraction, wt %	low content		Less than 45
	medium content		45–57
	high content		More than 57
Gas saturation of oil, m3/t	with low gas saturation		Less than 200
	with medium gas saturation		200–500
	with high gas saturation		More than 500
Hydrogen sulfide content, wt %	with low content		Less than 5
	with high content		More than 5
Vanadium content, wt %	with low content		Less than 0.003
	with high content		More than 0.003
Nickel content, wt %	with low content		Less than 0.007
	with high content		More than 0.007