Determination of C15-C20 isoprenoid alkanes characteristic ratios in the oils from Kazakhstan fields

Aiken B. Zhamanbayeva, Olga Yu. Kurtova, Mereke B. Alimzhanova, И. Г. Зенкевич

2019

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DOI 10.15826/analitika.2019.23.2.011
Data confidence 85 high
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Abstract

Seven samples of crude oil from Kazakhstan fields are characterized with the ratios of isoprenoid alkanes (biomarkers), namely “pristane / phytane” ( R 1), “phytane / n -octa­decane” ( R 2), and “pristane / n -heptadecane” ( R 3). Additionally, the following ratios rarely taken into account were also considered: “pristane / 2,6,10-trimethylpentadecane (norpristane)” ( R 4), “pristane / 2,6,10-trimethyltetradecane” ( R 5), and “pristane / 2,6,10-trimethyltri­de­cane” ( R 6). It was concluded that the higher were the relative standard deviations of R -criteria (va­riation coefficients, d N , %) within series of any sample, the higher were their informative­ness for distinguishing these samples. For instance, d N -values for criteria R 1 – R 3 were 36-62%, while for R 4 – R 6 they were 2-3 times less (13-34%). The reproducibility of R -criteria both at fixed conditions of analysis and at any vari­ations of gas chromatographic separation parameters was characterized. In both cases the relative standard deviations (d i , %) for criteria R1 – R 3 were approx. 3%, while for crite­ria R4 – R 6 – about 10%. Combining both parameters d N and d I allowed intro­du­cing the integral criterion for distinguishing the petroleum samples, K = d N / d i . K -Values for crite­ria R 1 – R 3 varied within the range of 8-41, while those for criteria R 4 – R 6 varied within the range of 1.2-2.4, i.e., 10-20 times less. It means that expanding the lists of isopreno­id alkanes as biomarkers by considering such minor constituents as norpris­tane, 2,6,10-trimethyl­tetradecane, and 2,6,10-trimethyltridecane seems to be irrational due to the low information content. Keywords : Crude oil, Kazakhstan fields, gas chromatography, isoprenoid alkanes C 15 -C 20 (phytane, pristane, 2,6,10-trimethylpentadecane, 2,6,10-trimethyltetra­decane, 2,6,10-trimethyltridecane, farnesane), characteristic ratios, reproducibility at different con­ditions of analysis DOI: http://dx.doi.org/10.15826/analitika.2019.23.2.011 (Russian) 1 Aiken B. Zhamanbayeva, 2 Olga Yu. Kurtova, 1 Mereke B. Alimzhanova, 2 Igor G. Zenkevich 1 Al-Farabi Kazakh National University, prosp. Al-Farabi, 71, Almaty, 050040, Kazakhstan 2 St. Petersburg State University, Institute for Chemistry, Universitetskii prosp., 26, St. Petersburg, 198504, Russian Federation