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Use of Light Hydrocarbons Combined Biomarkers for Oil-Oil Correlations From the Pearl River Mouth Basin, Southeastern China

Abstract

We firstly apply the Mongo parameters on oils from the Pearl River Mouth Basin for oil-oil correlations, and divide them into families A, B and C. To validate the classification, we apply some common-used biomarker parameters on oil-oil correlations, including terpenes, steranes, benzothiophenes, isoparaffin and N-alkanes etc. It is well-known that C5-C13 compound groups in the crude oils can serve as reliable parameters for oil-oil correlation because the C5-C13 light fractions are the major oil components, especially in light oil or condensate, in which they account for almost 90% of the whole oil. In this study, 34 oil samples were analyzed by using gas chromatography with flame ionization detector (GC-FID), GC with mass spectrometry (GC-MS) and comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC×GC-TOFMS), respectively. Firstly, compounds in gasoline range (i-C5H12-n-C8H18) were identified and quantified by directly injecting the oil samples to GC-FID. Secondly, the oil samples were further analyzed by GC-MS and GC×GC-TOFMS, and more than 300 compounds were identified and quantified, including terpenes, steranes, aromatic hydrocarbons, polyaromatic hydrocarbons, and heteroaromatic sulfur-, oxygen-, and nitrogen -containing compounds. By analyzing the relative concentrations of n-heptane, dimethyl cyclopentane and methyl cycohexane, the oils were divided into 3 groups: Humic type, sapropelic type and mixed type, which were further validated by the distribution of biomarkers such as C30–4-methyl sterane, bicadinane, pristane, phytane and fluorene series etc. Similarly, the 34 oil samples were classified by using the relative concentrations of the above biomarkers and 3 oil families were obtained, which is in good agreement with the results from light hydrocarbons. Family A derived from source rock of deep lake sedimentary facies from Wenchang formation, which are rich in C30–4-methyl sterane but lack of bicadinane. Family B is rich in bicadinane but lack of C30–4-methyl sterane, which indicates the oils are generated from Enping formation. Family C is the mixed type, which is abundant with both C30–4-methy sterane and bicadinane. Additionally, the relative concentrations of dibenzothiophenes, dibenzofurans and fluorenes, and the ratio of pristane to phytane were analyzed, and the same conclusion was obtained, which provide reliable evidence for the oil-gas exploration from Pearl River Mouth Basin.