69 D32. Geochemistry (Posters)

Sunday, 22 October 2017
9:00 AM - 5:30 PM
Halls 4EF

CATALYTIC GENERATION OF METHANE AT 60 TO 100 °C AND 0.1 TO 300 MPA FROM SOURCE ROCKS CONTAINING KEROGEN TYPES I, II, AND III

Paper number: 69-13
Program: Technical Sessions
Time: 9:00 AM – 5:30 PM

Authors

  • Lin Wei Presenting Author
    institute of unconventional natural gas, Beijing

Abstract

Low temperature (60 and 100 °C) and long-term (6 months to 5 years) heating of pre-evacuated and sterilized shales and coals containing kerogen Types I (Mahogany Shale), II (Mowry Shale and New Albany Shale), and III (Springfield Coal and Wilcox Lignite) with low initial maturities (vitrinite reflectance Ro0.39 to 0.62%) demonstrates that catalytically generated hydrocarbons may explain the occurrence of some non-biogenic natural gas plays where insufficient thermal maturity contradicts the conventional thermal cracking paradigm.

Our laboratory experiments utilized source rock chips sealed in gold and Pyrex® glass tubes in the presence of hydrogen-isotopically contrasting waters. Parallel heating experiments applied hydrostatic pressures from 0.1 to 300 MPa. Control experiments constrained the influence of pre-existing and residual methane in closed pores of rock chips that was unrelated to newly generated methane.

This study’s experimental methane yields at 60 and 100 °C are 5 to 11 orders of magnitude higher than the theoretically predicted yields from kinetic models of thermogenic methanogenesis, which strongly suggests a contribution of catalytic methanogenesis. Higher temperature, longer heating time, and lower hydrostatic pressure enhanced catalytic methanogenesis. No clear relationships were observed between kerogen type or total organic carbon content and methane yields via catalysis. Catalytic methanogenesis was strongest in Mowry Shale where methane yields at 60 °C amounted to ~2.5 μmol per gram of organic carbon after one year of hydrous heating at ambient pressure.

In stark contrast to the earlier findings of hydrogen isotopic exchange between water and thermogenic methane in hydrous pyrolysis experiments above 300 °C, the hydrogen isotopic composition of added water exerted limited influence on the δ2H value of methane generated catalytically at low temperatures. The δ13CCH4 values of methane generated catalytically at 60 to 100 °C range from ~-57.6 to -41.4‰ and are thus similar to typical thermogenic methane (δ13CCH4 > -50‰) and microbially generated methane (< -55‰).

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-298936

© Copyright 2017 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.