Geothermometry and geobarometry of overpressured lower Paleozoic gas shales in the Jiaoshiba field, Central China: insight from fluid inclusions in fracture cements

Gao, Jian, He, Sheng, Zhao, Jian-xin and Yi, Jizheng (2017) Geothermometry and geobarometry of overpressured lower Paleozoic gas shales in the Jiaoshiba field, Central China: insight from fluid inclusions in fracture cements. Marine and Petroleum Geology, 83 124-139. doi:10.1016/j.marpetgeo.2017.02.018


Author Gao, Jian
He, Sheng
Zhao, Jian-xin
Yi, Jizheng
Title Geothermometry and geobarometry of overpressured lower Paleozoic gas shales in the Jiaoshiba field, Central China: insight from fluid inclusions in fracture cements
Journal name Marine and Petroleum Geology   Check publisher's open access policy
ISSN 0264-8172
1873-4073
Publication date 2017-05-01
Sub-type Article (original research)
DOI 10.1016/j.marpetgeo.2017.02.018
Open Access Status Not yet assessed
Volume 83
Start page 124
End page 139
Total pages 16
Place of publication London, United Kingdom
Publisher Elsevier
Collection year 2018
Language eng
Abstract The Wufeng-Longmaxi organic-rich shales host the largest shale gas fields of China. This study examines sealed fractures within core samples of the Wufeng-Longmaxi shales in the Jiaoshiba shale gas field in order to understand the development of overpressures (in terms of magnitude, timing and burial) in Wufeng-Longmaxi shales and thus the causes of present-day overpressure in these Paleozoic shale formations as well as in all gas shales. Quartz and calcite fracture cements from the Wufeng-Longmaxi shale intervals in four wells at depth intervals between 2253.89 m and 3046.60 m were investigated, and the fluid composition, temperature, and pressure during natural fracture cementation determined using an integrated approach consisting of petrography, Raman spectroscopy and microthermometry. Many crystals in fracture cements were found to contain methane inclusions only, and aqueous two-phase inclusions were consistently observed alongside methane inclusions in all cement samples, indicating that fluid inclusions trapped during fracture cementation are saturated with a methane hydrocarbon fluid. Homogenization temperatures of methane-saturated aqueous inclusions provide trends in trapping temperatures that Th values concentrate in the range of 198.5 °C–229.9 °C, 196.2 °C-221.7 °C for quartz and calcite, respectively. Pore-fluid pressures of 91.8–139.4 MPa for methane inclusions, calculated using the Raman shift of C-H symmetric stretching (v1) band of methane and equations of state for supercritical methane, indicate fluid inclusions trapped at near-lithostatic pressures. High trapping temperature and overpressure conditions in fluid inclusions represent a state of temperature and overpressure of Wufeng-Longmaxi shales at maximum burial and the early stage of the Yanshanian uplift, which can provide a key evidence for understanding the formation and evolution of overpressure. Our results demonstrate that the main cause of present-day overpressure in shale gas deposits is actually the preservation of moderate-high overpressure developed as a result of gas generation at maximum burial depths.
Keyword Fluid inclusions
Geobarometry
Raman spectroscopy
Sichuan basin
Wufeng-Longmaxi shales
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: HERDC Pre-Audit
School of Earth and Environmental Sciences
 
Versions
Version Filter Type
Citation counts: TR Web of Science Citation Count  Cited 0 times in Thomson Reuters Web of Science Article
Scopus Citation Count Cited 0 times in Scopus Article
Google Scholar Search Google Scholar
Created: Tue, 11 Apr 2017, 00:25:16 EST by Web Cron on behalf of Learning and Research Services (UQ Library)