Formation mechanism and geochemical characteristics of shallow natural gas in heavy oil province,China |
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| Authors: | GuangYou Zhu ShuiChang Zhang WenZhi Zhao ZhengJun Wang YingBo Liang XueFeng Zhao JingYan Zhang |
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| Institution: | 1.Research Institutes of PetroChina Exploration and Development,PetroChina Oil Geologic Lab Center,Beijing,China |
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| Abstract: | Shallow gas reservoirs are distributed widely in Chinese heavy oil-bearing basins. At present, shallow gas resources have opened up giant potentials. The previous researches indicate the intimate genetic relationship between shallow gas and heavy oil. Shallow gas resources are generated from crude oil degraded by anaerobic microscopic organism, it belongs to biogenic gas family of secondary genesis, namely heavy oil degraded gas. Shallow gas resources are usually distributed in the upward position or the vicinity of heavy oil reservoirs. They are mainly of dry gas, which are composed of methane and only tiny C 2 + heavy hydrocarbon and relatively higher contents of nitrogen gas. Generally, methane isotopes are light, whose values are between biogenic gas and thermal cracking gas. Ethane isotopes are heavy, which mixed possibly with thermogenic gas. Carbon dioxide bear the characteristics of very heavy carbon isotope, so carbon isotopic fractionation effects are very obvious on the process of microscopic organism degradation crude oil. The heavy oil degraded gas formation, a very complex geological, geochemical and microbiological geochemical process, is the result of a series of reactions of organic matter-microbes and water-hydrocarbon, which is controlled by many factors. |
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