Geochemical Characteristics of the Jurassic Alkane Gas in the Muli Depression, South Qilian Basin: Implications for Potential of Light Oil and Condensate

The discovery of gas hydrates in the Muli Depression has made the South Qilian Basin (SQB) a hotspot for oil and gas exploration. Although many studies have been carried out on the gas hydrates, the geochemical characteristics have rarely been reported, which can effectively indicate the genetic typ...

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Main Authors: Furong Tan, Yang Li, Zhiqing Xie, Xiaowei Bian, Fangpeng Du, Shiming Liu, Ping Lu, Jingli Wang
Format: Article
Language:English
Published: Frontiers Media S.A. 2022-05-01
Series:Frontiers in Earth Science
Subjects:
Online Access:https://www.frontiersin.org/articles/10.3389/feart.2022.898629/full
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author Furong Tan
Furong Tan
Yang Li
Zhiqing Xie
Xiaowei Bian
Fangpeng Du
Shiming Liu
Ping Lu
Jingli Wang
author_facet Furong Tan
Furong Tan
Yang Li
Zhiqing Xie
Xiaowei Bian
Fangpeng Du
Shiming Liu
Ping Lu
Jingli Wang
author_sort Furong Tan
collection DOAJ
description The discovery of gas hydrates in the Muli Depression has made the South Qilian Basin (SQB) a hotspot for oil and gas exploration. Although many studies have been carried out on the gas hydrates, the geochemical characteristics have rarely been reported, which can effectively indicate the genetic type, diffusion, biodegradation, and thermal maturity of natural gas. In this contribution, the molecular composition and carbon isotopes of alkane gases were collected from gas hydrates and free gases in drilled boreholes of the Muli Depression. The results show that the majority of natural gases are oil-type gases, with a little coal-type gases. The natural gases have undergone biodegradation, leading to a decrease in the propane content and an increase in the methane content, with a heavier carbon isotope of propane and a lighter carbon isotope of methane. Some of the natural gases have experienced diffusion, resulting in a decrease in the methane content and an increasing value of Δ(δ13C1-δ13C2). Furthermore, the wet gases from natural gases were derived from the cracking of kerogen and crude oil at the thermal maturity stage. The dry gases in small quantities were produced by biodegradation of the wet gases. We propose that the potential for light oil and condensate exists in the Jurassic Yaojie Formation. Our new findings on the geochemical characteristics of natural gases provide new constraints for the study of petroleum systems and deeply buried sediments in the SQB.
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spelling doaj.art-9f2d174bcc114da29840e806d088fb542022-12-22T00:29:51ZengFrontiers Media S.A.Frontiers in Earth Science2296-64632022-05-011010.3389/feart.2022.898629898629Geochemical Characteristics of the Jurassic Alkane Gas in the Muli Depression, South Qilian Basin: Implications for Potential of Light Oil and CondensateFurong Tan0Furong Tan1Yang Li2Zhiqing Xie3Xiaowei Bian4Fangpeng Du5Shiming Liu6Ping Lu7Jingli Wang8State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an, ChinaShaanxi Institute of Geological Survey, Xi’an, ChinaState Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an, ChinaChina National Administration of Coal Geology, Beijing, ChinaShaanxi Institute of Geological Survey, Xi’an, ChinaCollege of Geology and Environment, Xi’an University of Science and Technology, Xi’an, ChinaKey Laboratory of Resource Exploration Research of Hebei Province, Hebei University of Engineering, Handan, ChinaState Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an, ChinaShaanxi Earthquake Agency, Xi’an, ChinaThe discovery of gas hydrates in the Muli Depression has made the South Qilian Basin (SQB) a hotspot for oil and gas exploration. Although many studies have been carried out on the gas hydrates, the geochemical characteristics have rarely been reported, which can effectively indicate the genetic type, diffusion, biodegradation, and thermal maturity of natural gas. In this contribution, the molecular composition and carbon isotopes of alkane gases were collected from gas hydrates and free gases in drilled boreholes of the Muli Depression. The results show that the majority of natural gases are oil-type gases, with a little coal-type gases. The natural gases have undergone biodegradation, leading to a decrease in the propane content and an increase in the methane content, with a heavier carbon isotope of propane and a lighter carbon isotope of methane. Some of the natural gases have experienced diffusion, resulting in a decrease in the methane content and an increasing value of Δ(δ13C1-δ13C2). Furthermore, the wet gases from natural gases were derived from the cracking of kerogen and crude oil at the thermal maturity stage. The dry gases in small quantities were produced by biodegradation of the wet gases. We propose that the potential for light oil and condensate exists in the Jurassic Yaojie Formation. Our new findings on the geochemical characteristics of natural gases provide new constraints for the study of petroleum systems and deeply buried sediments in the SQB.https://www.frontiersin.org/articles/10.3389/feart.2022.898629/fullSouth Qilian BasinMuli Depressionnatural gasstable carbon isotopessecondary alteration
spellingShingle Furong Tan
Furong Tan
Yang Li
Zhiqing Xie
Xiaowei Bian
Fangpeng Du
Shiming Liu
Ping Lu
Jingli Wang
Geochemical Characteristics of the Jurassic Alkane Gas in the Muli Depression, South Qilian Basin: Implications for Potential of Light Oil and Condensate
Frontiers in Earth Science
South Qilian Basin
Muli Depression
natural gas
stable carbon isotopes
secondary alteration
title Geochemical Characteristics of the Jurassic Alkane Gas in the Muli Depression, South Qilian Basin: Implications for Potential of Light Oil and Condensate
title_full Geochemical Characteristics of the Jurassic Alkane Gas in the Muli Depression, South Qilian Basin: Implications for Potential of Light Oil and Condensate
title_fullStr Geochemical Characteristics of the Jurassic Alkane Gas in the Muli Depression, South Qilian Basin: Implications for Potential of Light Oil and Condensate
title_full_unstemmed Geochemical Characteristics of the Jurassic Alkane Gas in the Muli Depression, South Qilian Basin: Implications for Potential of Light Oil and Condensate
title_short Geochemical Characteristics of the Jurassic Alkane Gas in the Muli Depression, South Qilian Basin: Implications for Potential of Light Oil and Condensate
title_sort geochemical characteristics of the jurassic alkane gas in the muli depression south qilian basin implications for potential of light oil and condensate
topic South Qilian Basin
Muli Depression
natural gas
stable carbon isotopes
secondary alteration
url https://www.frontiersin.org/articles/10.3389/feart.2022.898629/full
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