Petrochemical and hydrocarbon analysis

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Petrochemical and hydrocarbon analysis

Petrochemicals

The discovery of an oil field during petroleum exploration does not automatically guarantee success. The quality and properties of the hydrocarbons in the oil still need to be determined - things like the gas-oil ratio, viscosity and hydrocarbon composition. Given the mammoth cost of setting up a production facility, especially for deep water fields, it is imperative to know everything about the oil field for appropriate planning.

Once a field has been located, samples are withdrawn for detailed analyses but these can be complicated by contamination with the drilling fluids. Even when large volumes of crude oil are pumped out, diluting the contamination, the process must be monitored to ensure an accurate determination of the oil properties. A selection of drilling fluid types is available to prospectors, including traditional oil-based fluids. However, these are beginning to be replaced by the more environmentally friendly synthetic oil-based fluids, which are less harmful to the waters when they are pumped out in offshore operations.

The synthetic drilling fluids consist of mixtures of linear and branched alkenes, including 1-alkenes (the double bond at the end of the alkene chain) and internal alkenes (the double bond within the alkene chain). They contain a wide range of isomers, making them more difficult to characterise, especially within contaminated oils. The standard industry method is GC with flame ionisation detection (GC-FID) but scientists in the US have commented on some shortfalls in this technique.

Much better discrimination is gained when GCxGC is utilised in conjunction with ToF-MS where not only a second dimension  of separation (eg polarity) is possible but the very fast continuous beam ToF MS can deal with very narrow peaks or coeluting species.

The bar to the right shows some typical data obtained from crude oil after such analysis.