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 Technology

thus shows the API, sulphur and also the 565°C+ values for the four samples. As stated in the introduction a full assay is not carried out on every crude delivery, and as can be seen from the value of 565°C+ in Table 1, this can vary between batches for the same crude. API and sulphur analysis therefore does not always provide sufficient information to properly evaluate the value of each crude cargo. In Table 1 samples_01, _02, and _04 form a group with similar properties; however, sample_03 is different. The API of sample_03 would suggest a lighter crude but the 565°C+ cut is double the other members of this group. If this pattern were repeated then 25 per cent of the crude cargos being processed would have twice as much residue as expected.

The Aggregate plot InBlend utilises specially tuned plots (known as aggregates) which show the spectral variation within a crude type. Figure 1 shows an aggregate plot of a group of crudes from the same geographical location within the global crudes database. The trend in the aggregate plot is that API gravity is lower in the lower right of the box and increases as the crudes get lighter to the upper left of the box. This can be seen also in the 565°C+ property aggregate where the heavier crudes with the higher 565°C+ are in the lower right of the box and lighter crudes with less 565°C+ are in the upper right of the box. The points are colour coded, and the higher the value of the property the darker the colour.

Figure 3: TBP curves for all four crude samples

Crude type XX analysis The aggregate plot in Figure 2 shows how sample_03 is identified by the spectra as being different from the other three samples. The crude is shown as a red point. The API of this crude is 37.9 (Table 1) and thus indicates that it is the lightest of the four crudes in question. Looking at the sulphur content it can be seen it is 0.3 that is the lowest sulphur content of the four, once again suggesting this would be the lightest and most valuable of these four crudes. Due to this obvious outlier, further investigation of this crude was carried out. Shown in Figure 3 is the laboratory TBP curve of the four crudes. It can be clearly seen that sample_03 is different to the other three samples and that the TBP curves of the other three samples are very similar. As stated before InBlend can predict the properties of a crude sample purely from a NIR spectrum. Shown in Figure 4 the predicted TBP for the four samples can be seen.

Figure 4: TBP curves from InBlend prediction

The distillation curves show clearly that sample_03 is heavier than the other three samples, having more 565°C+ residue. Looking at the predicted values it can be seen they follow the same trend as the actual values. It is also important to note that the outlying crude has been predicted to be different to the other crudes in the same family. This prediction has been made based purely on the NIR spectra and thus the technology ignores the other crudes of the same family for sample_03 because spectrally they are further away. The technology thus uses other spectra that are close to sample_03 and predicts the spectra.

Conclusion

Figure 2: Aggregate plot of crude type XX showing cluster and difference

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Issue 7 2016

This case study clearly demonstrates that whole crude property measurements are not a conclusive method of characterising a crude type to give a refinery the real value of a crude import. In this case the crude sample_03 has a higher API suggesting a lighter crude oil; however, looking at the aggregate plot shows that it is different and the InBlend prediction calculates that whilst the light ends are greater, the 565°C+ cut is higher compared to the rest of its crude type. Furthermore, netback calculations were performed of the above crude and it was found that the refiner was losing more than US$1/barrel on every barrel of this crude processed, due to the difference in crude oil quality. Due to the analysis undertaken, the refiner was able to re-optimise his blend to the actual TBP and ensure consistency in quality provided to the trader. n

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Oil Review Middle East 7 2016  

Oil Review Middle East 7 2016