Full Range Crudes, Analytical Methodology of
Authors: Ali M.A. 
Published: September 2006

Crude oil at the wellhead is a hot, high pressure fluid that contains gases, oil, water vapor and solid impurities. This mixture is processed in a gas oil separator where it is brought to atmospheric pressure and separated into gases, water, solid and stabilized oil. Characterization of a stabilized crude oil is carried out using a number of analytical methods for both its physical and chemical properties. These methods include use of a densitometer for density measurement and a hydrometer for specific gravity and American Petroleum Institute (API) gravity. The densitometer provides more precise and reproducible measurement of density as well as better control of the temperature of the sample. Pour point is determined using a cooling and pouring method, water content determination by distillation, ash content by a high temperature burning method, while salt content of a crude is determined by an electrometric method. The metal contents are determined using inductively coupled plasma atomic emission spectrometry (ICPAES) and atomic absorption spectrometry (AAS). The ICPAES is faster as compared to AAS and provides simultaneous determination of a wide range of metals. The elemental analysis is carried out by oxidative combustion of the sample in which carbon, hydrogen and sulfur are measured in oxide form, while nitrogen is measured in the form of molecular nitrogen. Sulfur is also determined using atomic emission spectrometry (AES) and chemiluminescent detectors which are very sensitive as compared to the oxidative combustion method. In addition, chemiluminescent detectors also provide nitrogen determination. Molecular weight is determined using thermoelectric measurement of vapor pressure; however the values obtained are influenced by the temperature of the measurement and the type of solvent used for dissolving the sample. Gel permeation chromatography (GPC) is used for average molecular weight determination of crude oil. Physical distillation is used for producing light and middle distillates and residue fractions based on the desired boiling range or volume percent range of a crude oil as well as determination of the boiling range distribution. Gas chromatography (GC) is utilized for determination of boiling range distribution by simulated distillation, volatile compound determination and identification of crude oil spill. The faster analysis time, better reproducibility and equivalent results are some of the advantages of simulated distillation over physical distillation in the determination of the boiling range distribution of a crude oil. Gas chromatography/mass spectrometry (GC/MS) separates and identifies volatiles and low boiling components of a crude oil while mass spectrometry (MS) is utilized for assessing the molecular weights of the compounds. High‐performance liquid chromatography (HPLC) is used for separation and quantification of hydrocarbon group types such as saturates, aromatics and polars. Aromatics are further separated into monoaromatics, diaromatics, triaromatics and polyaromatics. Liquid chromatography (LC) is used to fractionate the whole crude oil into desired fractions such as acids, bases and neutral nitrogen compounds. Petroleum resins are separated from whole crude oil by a liquid chromatographic method using ion‐exchange resins. Liquid chromatography/mass spectrometry (LC/MS) provides separation and positive identification of high boiling compounds of a crude oil. Supercritical fluid chromatography (SFC) is used for separation and identification of hydrocarbon group types. Compared to HPLC, SFC provides better separation of high boiling components. Infrared (IR) spectroscopy is used for determination of type of functional group and hydrogen bonding, thermal analysis for evaluating the thermal stability of the crude oils and classification of hydrocarbons while titrimetry is used for determining acid number, base number and water content.