Molecular weight determination of crude oil samples is an important factor in the process of oil production in any oil field. This paper shows an experimental study to develop a correlation that numerically predicts the molecular weight of any crude oil sample with a known density.

The current method used in the laboratory to test the crude oil samples for average molecular weight value is the freezing point depression method, which is implemented in an automated cryometer 1 . This method takes a relatively long time to perform. The use of the developed correlation will help in predicting a numerical estimation of the expected average molecular weight value for each tested sample. It will also help as a quality check step on the values we get from the performed experiment. Moreover, if this correlation continues to give accurate results, it can be used as an alternative method to the laboratory test.

The author carefully analyzed experimental data of average molecular weight as well as density to look for a correlation that relates both quantities. The analyzed data was of crude oil samples from thirty different fields in the Saudi Arabian region. This analysis required assuming that density is the only factor affecting the molecular weight value at constant temperature and pressure.

After analyzing all the experimental data generated in the laboratory, we successfully developed a correlation that gives accurate and comparable results within 2% average error to the obtained experimental values. These results were found for samples from several but not all of the Saudi Arabian fields. The study did not include new exploration fields or fields with insufficient data. Furthermore, this study concentrates solely on black oil samples and excludes gas condensate samples.

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