CHARACTERISTICS OF BIOMARKERS IN PALEOZOIC OIL SEEPAGE FROM TARIM BASIN

This paper centers on the study of the marker characteristics of vug seepages which are from marine carbonate of the upper Carboniferous in Tarim Basin. The results show that the liquid seepage, collected from biogenic limestone, has a higher thermal maturity, a lower pristane-to- (Pr/Ph) ratio, a slight even to odd dominance in the n-alkanes,. a high content of higher molecular weight hopanes, and a slightly higher abundance of 17α. (H) 21 β (H) -C35 hopane relative to 17α (H) 21β(H) -C₃₄ hopane. All of those have a good correlation with extract of the surrounding rocks, which indicates that the vugs seepage was autochthonous. The paper has also studied on the geochemical characteristics of the asphalt veins in the limestone fissures of the lower Ordovician in the basin. It is proved that the biomarkers of as- phalt veins are mainly composed of 25-nor hopanes, 8, 14-secohopanes and ring-D-aromatic 8, 14- secohopanes; and the aromatics of asphalt veins have a intensive demethylized career; Phenanthren in it takes a percentage of 72.5 in phenanthrenoids. Obviously by analysing the geologic information, the asphalt was formed by the material originated from the crud oil of the deep part in the basin, underwent a higher geothermal alteration and the microbial-biodegradation and oxidation . It is obivous that the result mentioned above may provied important information for the assessment of petroleum prospect in the deep part of the basin.