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The oil discovery in the Precambrian basement fractured buried-hills of the Bongor Basin, Chad, is a milestone for the African onshore exploration play. Geochemical techniques including GC, GC/MS were adopted to analyze the biomarker composition and geochemical characteristics of oils from the Baobab buried-hill and shales from the Baobab N and Mimosa (MM) sags, respectively. The oil-source correlations were carried out for the buried hill oils and source rocks of BN/MM sags, and the hydrocarbon accumulation process was interpreted based on the thermal evolution history. The results indicate that BN/MM sags have contributed to the oils of the Baobab buried-hill field along with two phases of hydrocarbon accumulations. The MM sag started to expel hydrocarbon in the middle Late Cretaceous (about 85 Ma), and then in the late Late Cretaceous (about 70 Ma) both the MM and BN sags expelled hydrocarbons for the Baobab buried-hill trap. [ABSTRACT FROM AUTHOR]

In the future time the exploration of marine oil and gas will be one of the significant domains in China. In this paper the biomarker assemblage characteristics of oilshow in the Nanlinghu Formation of the Majiashan profile, which is located in Chaoxian County, south of Anhui Province, are described in the light of gas chromatography/mass spectrometric (GCMS) analysis on the qualitative and quantitative basis. Based on the investigation of the biomarker assemblage characteristics of possible source rocks developed in the area studied, a conclusion is drawn that the oilshow was generated from the Nanlinghu Formation source rocks (abbreviated as T1 n), instead of the Qixia Formation source rocks (abbreviated as P1 q). It is pointed out that the T1 n is of strong potential for future oil exploration, and therefore much attention should be paid to it. [ABSTRACT FROM AUTHOR]

The geochemical characteristics of natural gases discovered in the Bozhong Depression are systematically described in this paper. The natural gases are composed mainly of hydrocarbon gases. Natural gases occurring in the Paleogene and older reservoirs are wet gases, whereas those in the Neogene reservoirs are dry gases. Methane and ethane in the gases are significantly different in carbon isotopic composition. The methane carbon isotopic composition of the gases in structure BZ28-1 and the ethane carbon isotopic composition of the gases in structure QHD30-1 are characterized by the heaviest values, respectively. The natural gases are in the mature to highly mature stages. The hydrocarbon gases are of organic origin and can be classified as oil-type gases, coal-derived gases and mixed gases with the third one accounting for the major portion. [ABSTRACT FROM AUTHOR]

The central Junggar Basin in western China is unique because it provides insights into the geochemistry of oil from Jurassic coal measures. The analysis of TOC, Rock-Eval pyrolysis, gas chromatography-mass spectrometry (GC-MS), and carbon isotopes was performed to characterize the oil geochemistry and evaluate the hydrocarbon generation potential of source rocks in a coal-bearing formation. Fluid inclusions, fluorescence microscopy, and burial-thermal history were also used to study the oil generation and charging histories. The results show that the mudstone of the Badaowan Formation is the main source rock of the Jurassic and has relatively high hydrocarbon generation potential. The Jurassic oil in the Zhong-4 Block is moderately mature, with an equivalent Ro of about 0.75%. The oil is characterized by heavy carbon isotopes, a predominance of Pr over the Ph, low abundances of trisnorhopane (Ts), tricyclic terpanes and gammacerane, predominance of C 29 steranes among regular steranes, a preponderance of naphthalene and its alkylated analogues in aromatic compounds, and abundant polycyclic compounds. Such geochemical data indicate a contribution of Jurassic humic type organic matter to the oil. The mudstone in the Badaowan Formation started generating hydrocarbons in the Early Cretaceous and reached the peak of hydrocarbon generation in the middle Cretaceous. One major hydrocarbon charging episode is suggested in the Late Cretaceous and another in the early Neogene. The Fukang Depression in the south is the source kitchen, and oil migrates in a direction of southwest to northeast through faults and sandstone carrier beds. • The Jurassic mudstones and oils are mostly within the oil window. • The mudstone in Badaowan Formation is the primary Jurassic source rock. • Unique biomarker characteristics of the Jurassic oil are demonstrated. • The Jurassic oil shows heavy carbon isotopes (δ 13 C > -28‰). • Two major hydrocarbon charging periods for the Jurassic reservoirs are suggested. [ABSTRACT FROM AUTHOR]