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- Title
The distribution and origin analysis of natural gas in Langgu Sag,Bohai Bay Basin.
- Authors
Wang Quan; Cao Yi-jun; Diao Fan; Zhang Jin-feng; Guo Liu-xi; Zou Hua-yao
- Abstract
Based on the analysis of the natural gas component and its isotope,coupled with geochemical characteristics of source rocks and geological settings,the genetic type and distribution of natural gas of Langgu Sag were investigated. Analytical results show that great difference of geochemical characteristics exist between the shallow burial reservoirs (<1 900m)and deep burial reservoirs(>1 900m),displaying different genetic types.The shallow gas reservoirs are dominated by secondary biologic modification gas reservoirs with mixed secondary biogenic gas from biodegradation of thermogenic gas and residual thermogenic gas. And this type of gas is featured by high gas dry coefficient(>95%),but also relative high content of heavy gas(ΣC2+>0.5%);significant increase of isoparaffin content and significant decrease of propane;the partially reversed carbon isotope order with anomalously heavy propane carbon isotope compositions;light stable carbon isotope (-60‰<δ13C1<-50‰) of methane. The deep gas is mainly humic-prone and generated from the primary cracking of kerogen. Maturity estimation combined with pyrolysis of the source rocks reveal that most deep gas samples are derived from E2sL3 source rock interval with low to moderate value of RO ranging from 0.5% to 0.8%,while four gas samples from deep depth in the area of Caojiawu and Gu’an as well as samples from Ordovician buried-hilled may be generated from the E2s4-Ek source rock with high value of RO varying from 1.1% to 1.5%. It is concluded that the kerogen type and maturity of the source rock control the distribution of deep gas and the activity of hydrocarbon-connecting faults may play an important role on the formation of shallow gas reservoirs. The secondary biologic modification gas reservoirs occur in the areas of Gu’an,Liuquan and Langdong. Also significant attention must be focused on the potential of deep natural gas resource and the Daxing conglomerate body in the Gu’an-Jiuzhou and the Bieguzhuang's buried hilled are the favorable targets zone of further exploration for the deep natural gas.
- Subjects
NATURAL gas; GAS reservoirs; GEOLOGICAL basins; GEOCHEMISTRY; BIODEGRADATION
- Publication
Natural Gas Geoscience, 2017, Vol 28, Issue 9, p1
- ISSN
1672-1926
- Publication type
Article
- DOI
10.11764/j.issn.1672-1926.2017.08.019