Geochemical characteristics and genetic mechanism of the high-N2 shale gas reservoir in the Longmaxi Formation, Dianqianbei Area, China

Autor:	Zhao Zhang, Ji-Lin Li, Xin Wang, Jiehui Zhang, Honglin Shu, Rao Daqian, Yan-Jun Li, Xing Liang, Tingshan Zhang
Rok vydání:	2020
Předmět:	020209 energy Geochemistry Energy Engineering and Power Technology chemistry.chemical_element 02 engineering and technology 010502 geochemistry & geophysics 01 natural sciences Nitrogen generator chemistry.chemical_compound Geochemistry and Petrology 0202 electrical engineering electronic engineering information engineering Organic matter Rayleigh fractionation 0105 earth and related environmental sciences chemistry.chemical_classification Dry gas Geology Geotechnical Engineering and Engineering Geology Nitrogen Mineral resource classification Geophysics Fuel Technology Hydrocarbon chemistry Environmental science Economic Geology Oil shale
Zdroj:	Petroleum Science. 17:939-953
ISSN:	1995-8226 1672-5107
DOI:	10.1007/s12182-020-00456-8
Popis:	As an important pilot target for shale gas exploration and development in China, the Longmaxi Formation shale in the Dianqianbei Area is characterized by high content of nitrogen, which severely increases exploration risk. Accordingly, this study explores the genesis of shale gas reservoir and the mechanism of nitrogen enrichment through investigating shale gas compositions, isotope features, and geochemical characteristics of associated gases. The high-nitrogen shale gas reservoir in the Longmaxi Formation is demonstrated to be a typical dry gas reservoir. Specifically, the alkane carbon isotope reversal is ascribed to the secondary cracking of crude oil and the Rayleigh fractionation induced by the basalt mantle plume. Such a thermogenic oil-type gas reservoir is composed of both oil-cracking gas and kerogen-cracking gas. The normally high nitrogen content (18.05%–40.92%) is attributed to organic matter cracking and thermal ammoniation in the high-maturity stage. Specifically, the high heat flow effect of the Emeishan mantle plume exacerbates the thermal cracking of organic matter in the Longmaxi Formation shale, accompanied by nitrogen generation. In comparison, the abnormally high nitrogen content (86.79%–98.54%) is ascribed to the communication between the atmosphere and deep underground fluids by deep faults, which results in hydrocarbon loss and nitrogen intrusion, acting as the key factor for deconstruction of the primary shale gas reservoir. Results of this study not only enrich research on genetic mechanism of high-maturity N2 shale gas reservoirs, but also provide theoretical guidance for subsequent gas reservoir resource evaluation and well-drilling deployment in this area.
Databáze:	OpenAIRE
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