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Compared to the relatively high concentrations of nC10 - 20 in crude oils and gas condensates (analysed as unadulterated “Whole” sample) the concentrations of > nC30 can be relatively low and close to or below the limit of detection / quantification of the HTGC system. This is especially true for > nC50 and means that the values reported for these heavier n-alkanes may not have the same degree of accuracy as lower molecular weight n-alkanes or cannot be accurately determined at all.

To mitigate this problem the < nC15 fraction is removed through a “Topping” procedure (usually evaporation) which, in effect, concentrates the > nC20 fraction so that, even at the high end, peak areas are enhanced allowing them to be more accurately measured.

Results for “Whole” and “Topped” samples are then merged. This is achieved by adjusting the results from the “Topped” fraction so that the peak area of a chosen peak is normalised between the two samples. A peak around nC20 is usually chosen as this will have been present in sufficient quantities in the “Whole” sample for an accurate reading to be obtained (i.e. above the limit of detection) but is not removed by the “Topping” procedure.

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Partnerships with Plymouth Univeristy Logo

T-SEP® is a proprietary, small scale, thermal separation technique that has been developed by KAT in partnership with Plymouth University, primarily as a novel “Topping” method for crude oil and condensate samples although it is also applicable to a number of other processes.

This technology enables precise control over the “Topping” process and is more reproducible and effective than the simple evaporation techniques employed by most laboratories, allowing on average an additional 20 carbon numbers to be observed and measured.

“Topped” Sample Chromatograms With (red) and Without (blue) T-SEP® Enhanced Sample Preparation

n-Paraffin Weight Distributions With and Without T-SEP® Enhanced Sample Preparation

In addition to extending the analysis of the parent hydrocarbon fluids, T-SEP® is regularly used to enhance the analysis of associated deposits and has also been used in the semi-quantitative fingerprinting of semi-solid tar-balls.