Compositional Changes of Heavy Oil and Hydrocarbon from Nahotoka Oil -Primary Change in Spilled Oil during First Month in Seawater-

島根大学金沢大学大学院自然科学研究科Scedule:17-18 March 2003, Vemue: Kanazawa, Japan, Kanazawa Citymonde Hotel, Project Leader : Hayakawa, Kazuichi, Symposium Secretariat: XO kamata, Naoto, Edited by:Kamata, Naoto

Vertical Changes of Recent Ostracode Assemblages and Environment in the Inner Part of Jakarta Bay, Indonesia

A short sediment core from the inner part of Jakarta Bay, Indonesia, was quantitatively analysed for ostracods (minute Crustacea), total organic carbon (TOC) and total nitrogen (TN) contents, and the vertical distributions were recorded. A total of 53 ostracod species were obtained from 80 continuous core samples. The dominant species were Keijella carriei and Loxoconcha wrighti, which are common in areas with high TOC and TN contents. Based on an analysis of ostracod assemblages and carbon/nitrogen ratio, the study site began to be influenced by organic contamination from around 1950. Although the population of Jakarta City has increased rapidly since then, TOC and TN contents which were low, have gradually increased (0.7%–0.9% and 0.10%–0.12%, respectively), probably due to addition of nutrients from river sedimentation. The increased sedimentation rate after 1950 resulted in an increasing TOC ratio. The observed correlation between TOC and dominant species shows that Phlyctenophora orientalis may be a good indicator for monitoring increases in the narrow TOC content range of 0.7%–1.1%

Ⅲ.Chemistry

島根大学金沢大学大学院自然科学研究科 環境科学Editor : Tazaki, Kazue |田崎, 和

Organic geochemical evaluation of contamination tracers in deepwater well rock cuttings from the Mannar Basin, Sri Lanka

Abstract Geochemical data from rock-cutting samples can give rise to faulty interpretations due to contamination from drilling fluids used in modern deepwater petroleum exploration. In this study, oil-based drilling contaminants were removed by solvent extraction with dichloromethane and methanol (9:1) solution. Bulk and molecular organic geochemical characteristics were examined for both oil-based drilling mud and cleaned rock-cutting samples. Total organic carbon (TOC) values are notably high in heavy liquid oil-based drilling mud mixtures (TOC = 21.4–63.3%, average = 34.6% ± 8.6) compared to cleaned rock cuttings (TOC = 0.4–1.5%, average = 0.8% ± 0.3). In addition, drilling mud mixtures contain higher concentrations of unresolved complex mixtures (UCM) in the n-alkanes fraction. Therefore, it is difficult to distinguish individual homologues in the n-alkanes fraction. The triterpanes also have relatively high UCM contents compared to steranes fractions. However, hydrocarbon homologues can be identified in both the triterpanes and steranes fractions of oil-based drilling mud mixtures. Gas chromatograms indicate that the n-alkanes fractions of rock cuttings initially cleaned with solvent still show considerable contamination from drilling fluids. This remaining contamination was removed by an additional cleaning step using the soxhlet extraction technique. The triterpanes fraction in solvent-cleaned rock cuttings does not contain an overprint of heavy liquid oil-based drilling mud contamination. However, solvent-cleaned rock cuttings may still retain contamination signatures at the sterane C28-20R homologue due to coelution. The geochemical overprint of contaminants in the cleaned rock cuttings can be interpreted as infiltration of lower molecular weight compounds into micro-cracks of the cuttings. The distribution of these molecules varies in each hydrocarbon fraction. Therefore, close inspection of contamination effects is required before interpretation of traditional organic geochemical proxies such as source rock characteristics and maturity