Two case studies of oil-source correlation: Neo-Mesoproterozoic oil seeps and Paleogene oil pools in the north margin of the Bohai Gulf Basin
Creators: name: Mu, Guoyan
Publisher: name: Macquarie University
Year: 2022
Subjects: Other education not elsewhere classified

description: Oil-source correlations are based on the concept that certain compositional parameters of migrated oil do not differ significantly from those of bitumen remaining in the source rocks. This similarity though heritage can range from bulk properties, such as stable carbon isotope compositions, to individual compound ratios. Detailed oil-source rock correlations provide important information on the origin and possible paths of migration of oils that lead to additional exploration plays, and are helpful for reconstructing petroleum reservoir accumulation histories and fuel resource assessments. Biomarkers play a critical role in geochemical correlations. However, for Precambrian organic matter, there are significant difficulties doing oil-source rock correlations because of the likely high thermal maturity of the sedimentary organic matter, the sometimes low organic matter abundance, the small amount of geochemical information, and problems of contamination and over-printing. For highly mature exploration areas, attempts to objectively analyse the geochemical characteristics of crude oils based on a large geochemical data set, and how to evaluate source rocks more accurately, so as to improve the understanding of reservoir relationships and predicting petroleum resource are becoming more urgent problems at the moment. In this thesis, two representative fields were selected, the Neo-Mesoproterozoic sequence of the Yanshan Region and the highly mature exploration area of the Western Depression of the Liaohe Basin, in order to specifically answer correlation and other geochemical problems. -- The first of these case studies involves the marine sediments of the Yanshan Region which are some of the least deformed and least thermally mature hydrocarbon-bearing Neo-Mesoproterozoic sequences in China. The oil shows and seeps are mainly distributed in the reservoir sequences of the Xiamaling Formation (ca.1368 Ma), Tieling Formation and Wumishan Formation, which are probably derived either from the underlying organic-rich Hongshuizhuang Formation, or from kerogen within the Gaoyuzhuang Formation, as there are no known source rocks in the section. The 27 m thick mudstone of the Hongshuizhuang Formation has total organic carbon (TOC) levels of up to 5.5% and eqRomarine of about 1.7%. The other potential source rock (dolomite from the Gaoyuzhuang Formation) has TOC levels around 2.7% with 2.2% eqRomarine. Three outcrop source rocks were sampled from these two sequences and kerogen catalytic hydrogenation was performed in order to get more geochemical information on these high thermal maturity samples. Another two source rocks from drilling cores using standard solvent extraction have been analysed by gas chromatography-mass spectrometry (GC-MS). As for the either contaminated or biodegraded oil seeps, two samples rich in oil-bearing fluid inclusions (FI), (1) a limestone sample from the Tieling Formation, and (2) a bitumen sandstone from the Xiamaling Formation, were chosen for detailed analyses by the Molecular Composition of Inclusions (MCI) protocols. In addition, twenty samples from the reservoirs have been sequentially extracted as a supplement to the MCI analysis.