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S.P. Singh1, M. Bisht2, G.C. Dutta2, Kuldeep chandra2, Himmat Singh3
(1) ONGC Ltd, Dehra Dun, India
(2) ONGC Ltd
(3) IIP, Dehra Dun

Abstract: Assessment of maturity levels and structural features of crude oils of Cauvery Basin by aromatic biomarker distribution and NMR based parameters

The distribution of methyl phenanthrene isomers, their ratios, 13C NMR and 1H NMR techniques are used worldwide to generate structural and compositional data and to establish maturity level of oils. The paper presents the application of NMR spectroscopy and aromatic biomarkers to have a more comprehensive picture on maturity levels and compositional variations in crude oils of Cauvery basin. Thirteen representative oil samples were selected from all the important producing formation of different sub basins on the basis of variations in their gross compositions and normal / iso-alkane distribution. 1H and 13C NMR data has been combined to generate relatively accurate proton and carbon distribution data. The parameters like percentage of aromatic proton, average chain length, %Car, % Car.alk , %, % Car.H, % Car.b, have been employed to identify thermal evolutionary stages of oils while parameters like Csat, Cn-p, Ci-p, Cp, Cn, C/H, have been calculated to understand structural composition of crude oils. The study reveals that in Ariyalur Pondicherry sub-basin oil BV-2 of Sattapadi formation is of higher maturity level than oil BV-6 of Bhuvangiri formation, however both the oils have similar source organics as reflected by n-alkane/iso-alkane distribution. In Tanjore - Tranquebar sub basin the Basement oil MT-2 and PU-2 are similar in maturity levels but different in their source organics, while oil MT-1 of Nannilam formation has difference in maturity as well as source input. In the Nagapattinam sub-basin, the Cretaceous oil KV-17 of Bhuvangiri formation and oil VJ-2 of Nannilam formation indicate higher maturity levels while other oils are of similar maturity levels. 1H & 13C NMR parameters are found comparable to aromatic biomarkers for maturity assessment of crude oils.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana