Geochemistry of selected crude oils from Sabah and Sarawak

Author : Awang Sapawi Awang Jamil, Mona Liza Anwar & Eric Seah Peng Kiang
Publication : Bulletin of the Geological Society of Malaysia
Page : 123-149
Volume Number : 28
Year : 1991

Bulletin of the Geological Society of Malaysia, Volume 28, November 1991, pp. 123 – 149

Geochemistry of selected crude oils from Sabah and Sarawak


PETRONAS Petroleum Research Institute, Lot 1026, PKNS Industrial Estate, 54200 Kuala Lumpur


Abstract: A total of 35 crude oils from 15 fields from offshore Sabah and Sarawak have been analysed and characterised using liquid and gas chromatography, and gas chromatography-mass spectrometry. 

The normal alkane distribution shows that the oils are of three different types, namely,

i) normal, non-waxy crude oils;

ii) waxy oils (high proportion of C20+ n-alkanes);

iii) biodegraded oils (less abundance of n-alkanes relative to isoprenoids). 

Biological marker distributions (i.e. steranes and triterpanes) show that the oils were derived from terrigenous source rocks containing mixtures of different types of landplant derived organic matter, including resins. Features of these distributions include the presence of relatively high concentrations of 18α(H)-oleanane, a number of resin-derived compounds, a predominance of C29 steranes compared to the relatively low concentrations of C28 and C27 steranes, and the absence of C30 steranes in all the samples.

Source rock matter for these oils were probably deposited under peat swamp environments, as indicated by the high pristine/phytane (>3.0) and pristine/nC17 (>1.0) ratios. Biological marker distributions indicate that the oils were generated from source rocks having maturities of 0.5% to at least 0.8% VRe (Vitrinite Reflectance Equivalent).