Crude Oil
Assays
A crude assay is a complete and definitive analysis of crude oil and of all its components. The complete crude assay will provide information on the gravity, viscosity, pour point, true boiling point (TBP) curve, and light end analysis up to C8 and C9, in addition to the properties of the fractions, lube distillates, and asphalt.
In order to complete the assay, the crude oil is distilled according to the standard provided in ASTM D86 and ASTM D1160, depending on the temperature range appropriate for the sample. The crude oil is distilled at atmospheric temperature and separated into various fractions. The reduced oil is then further fractionated under a vacuum to produce vacuum gas oil, or VGO.
The crude oil assay indicates the distribution quantity and quality of the crude oil sample based upon its boiling point temperature range. At Texas OilTech Laboratories, we offer crude oil assay analysis to further identify the quality and grade of the crude oil sample, as well as provide a breakdown of information regarding the oil’s various components and characteristics.
Quality measures of the crude assay include specific gravity and API gravity, sulfur content, Octane number and Cetane number, viscosity, and carbon residue.
Fractionation
When crude oil is distilled under atmospheric pressure, the oil is reduced into various fractions, including naphtha, middle distillates, and gas oil residue. The crude oil is evaporated at different temperatures, which allows for the different substances within the mixture to condense at different times, depending on their boiling points. Substances with low boiling points (25°C), such as gases, condense at the top of the fractionating column, while middle distillates such as various liquids condense towards the middle of the column, while substances with high boiling points (350°C), such as most solids, condense at the bottom.
Main fractions resulting from crude oil fractionation include refinery gases, petrol or gasoline, naphtha for making chemicals, kerosene for aircraft fuel, diesel oil, fuel oil, and bitumen residue.
