Genetic types and geochemical characteristics of n

Authors: WenTao Li Yang Gao ChunYan Geng

Publish Date: 2015/01/22

Volume: 12, Issue: 1, Pages: 81-95

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Abstract

Natural gases were widely distributed in the Jiyang Depression with complicated component composition and it is difficult to identify their genesis Based on investigation of gas composition carbon isotope ratios light hydrocarbon properties as well as geological analysis natural gases in the Jiyang Depression are classified into two types one is organic gas and the other is abiogenic gas Abiogenic gas is mainly magmatogenic or mantlederived CO2 Organic gases are further divided into coaltype gas oiltype gas and biogas according to their kerogen types and formation mechanisms The oiltype gases are divided into mature oiltype gas oilassociated gas and highly mature oiltype gas The highly mature oiltype gases can be subdivided into oilcracking gas and kerogen thermal degradation gas Identification factors for each kind of hydrocarbon gas were summarized Based on genesis analysis results the genetic types of gases buried in different depths were discussed Results showed that shallow gases 1500 m are mainly mature oiltype gases biogas or secondary gases Secondary gases are rich in methane because of chromatographic separation during migration and secondary biodegradation Secondary biodegradation leads to richness of heavy carbon isotope ratios in methane and propane Genesis of middle depth gases 1500–3500 m is dominated by mature oiltype gases Deep gases 3500–5500 m are mainly kerogen thermal degradation gas oilcracking gas and coaltype gasThe Jiyang Depression is located in the north part of Shandong Province in China on the fluvial plain and the delta where the Huanghe River runs into the Bohai Sea Tectonically the Jiyang Depression is located in the southeast part of the Bohai Bay Basin It is a big terrestrial depression and ranks as one of the most prolific petroliferous area Li et al 2003 Since the discovery of the Shengli Oilfield in 1960 50 × 108 t of OOIP and 2500 × 108 m3 OGIP have been proved at the same time 107 × 108 tons of oil and 460 × 108 m3 gases have been produced

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