T20 The Unconventional Shale Systems: From Source-Rocks to Reservoirs I

Sunday, 22 September 2019
8:00 AM - 12:00 PM
Room 125AB, North Building

COMPOSITION AND ISOTOPIC CHARACTERISTICS OF UPPER PALEOZOIC MARINE-CONTINENTAL TRANSITIONAL SHALE GAS IN THE SOUTHEASTERN PART OF ORDOS BASIN, CHINA: APPLICATION TO GAS ORIGIN AND MIGRATION AMONG COMPLICATED LITHOLOGIES

Paper number: T20-6
Program: Technical Sessions
Time: 9:15 AM – 9:30 AM

Authors

  • Zhe Dong Presenting Author
    China University of Geosciences, Beijing, Beijing
  • Xuan Tang
    China University of Geosciences, Beijing, Beijing
  • Jinchuan Zhang
    China University of Geosciences, Beijing, Beijing
  • Zexin Su
    China University of Geosciences, Beijing, Beijing

Abstract

31 natural gas samples were collected from different lithologies including mudstone, sandstone and coal of Shanxi formation (P1s) and Benxi formation (C2b) in the southeastern part of Ordos Basin and the gas components, carbon and hydrogen isotope composition of gas samples were measured in this study. A remarkable difference in the ethane and carbon dioxide isotope values present between the natural gas from Shanxi formation and Benxi formation. The δ13C2 value of natural gas of Shanxi Formation generally is less than -30‰ whereas that of Benxi Formation is generally greater than -28‰, and the CO2 in Shanxi formation is mainly of organic origin while the CO2 in Benxi formation is mainly inorganic one. The difference between Shanxi and Benxi formation reveals that the gases in the two formations was preserved in two separated gas system, which may be attributed to existence of the tight mudstone and limestone between the reservoirs as effective barrier that prevent the gases from diffusion. Gases in the Shanxi Formation suffered strong diffusion, evidenced by homogenous gas component and isotope composition among various lithologies within Shanxi Formation, while no strong secondary alteration occurred in Benxi formation. The unusually depleted δ13C2 value found in Shanxi Formation was caused by the secondary cracking under extremely high thermal maturity and resulted in partial reversal of carbon isotope values (δ13C2<δ13C1), whereas this secondary cracking did not occur in Benxi formation, suggesting different organic matter and depositional environment may have effect on isotopic fractionation.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-336308

© Copyright 2019 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.