GENERAL BIOMARKER CHARACTERISTICS OF CRUDE OILS FROM NEW ZEALAND

The terrestrial oils of the Cretaceous and Tertiary from New Zealand have the special geochcmical characteristics, and the Quaternary oil is of unique singificance in the study of oil generation. Fifteen samples were collected from the Western Basin Province and Waiotapu high geothermal area in New Zealand, and the samples can be divided into three types: crude oils and condersates from producing oilfields; crude oils from non-commercial wells or coal exploration holes; and oil seepages. By the analysis of GC, carbon isotopes. GC-MS of saturates, it showed that the fifteen oils were formed in three types of conditions: 1. Oils formed in terrestrial marsh and shore-swamp environments, with great amount of plant input; the oils had the C29sterane predominance, the high pristane to phytane ratio and relatively light carbon isotopic composition. 2. Oils apparently biodegredated or water bleached, although the n-alkanes were destroyed, iso alkane are obvious and primarane is high; the characters of type 1 still remain. 3. Oils formed from the lacustrine sediments interlayered by volcanic ashes, with high thermal gradient and the anaerobic conditions, sulphur abundant medium. The oils are characteredc by C₂₇₊₂₈sterane predominance, evennumbered carbon predominance and the groupes of double peaks. The content of Gammarane is relatively high and the composition of carbon isotope is light. The maturity of New Zealand oils is not high, especially the oil from the Quaternary high thermal area is low mature.