Noble gases in Paleozoic shale fluids document tectonic events and fluid migration in the Upper Yangtze Block

Rui Liu, Tao Wen, Daniele L. Pinti, Rui Xu, Fang Hao, Shang Xu, Zhiguo Shu

Research output: Contribution to journalArticlepeer-review

Abstract

Major and noble gases of natural gas extracted from the low-permeability Paleozoic Wufeng-Longmaxi shale were measured to reconstruct the multi-stage, spatially varying tectonic evolution of the Upper Yangtze Block, China, one of the oldest parts of the Earth continents. The high gas dryness ratio [C1/(C2 + C3)] and high carbon isotopic ratios (δ13C-C1, δ13C-C2, δ13C-CO2) suggest a late mature thermogenic origin of shale gas. The highly fractionated atmospheric 20Ne/36Ar and 84Kr/36Ar ratios in our gas samples suggest they result from solubility-based partitioning of noble gases between oil and water followed by gas-water partitioning. Calculated volume ratios of oil, water, and gas phases vary spatially and temporally. In particular, the western Yangtze Block shows a lower reconstructed oil/water ratio, suggesting oil leakage promoted by the Triassic exhumation of Paleozoic shale, while a low gas/water ratio in the central-eastern Yangtze Block suggests gas leakage promoted by basin-wide Jurassic fold-thrust faulting. The lowest C1/36Ar volume ratio around faults at the basin edges indicates extensive gas expulsion. Delineated radiogenic 4He in gas samples are several orders lower than calculated in-situ produced radiogenic 4He, likely suggesting widespread 4He loss. Spatially-varying 4He/nucleogenic 21Ne ratios in the shale indicated that 4He loss in the western Yangtze Block predated that in the central-eastern portion. Such He loss was also coupled with the Triassic exhumation and the Jurassic fold-thrust faulting episodes. In summary, noble gas in pore fluids extracted from low-permeability shale can preserve reliable records of tectonic events produced during upper crust evolution.

Original languageEnglish (US)
Article number104671
JournalInternational Journal of Coal Geology
Volume297
DOIs
StatePublished - Jan 13 2025

Keywords

  • Fluid expulsion
  • Noble gases
  • Pore fluids
  • Shale
  • Tectonic deformation
  • Yangtze Block

ASJC Scopus subject areas

  • Fuel Technology
  • Geology
  • Economic Geology
  • Stratigraphy

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