Secondary gas emissions during coal desorption, Marathon Grassim Oskolkoff-1 Well, Cook Inlet Basin, Alaska: implications for resource assessment

Abstract

Research Article| September 01, 2006 Secondary gas emissions during coal desorption, Marathon Grassim Oskolkoff-1 Well, Cook Inlet Basin, Alaska: implications for resource assessment Charles E. Barker; Charles E. Barker Search for other works by this author on: GSW Google Scholar Todd Dallegge Todd Dallegge Search for other works by this author on: GSW Google Scholar Author and Article Information Charles E. Barker Todd Dallegge Publisher: Canadian Society of Petroleum Geologists Received: 30 Sep 2005 Accepted: 06 Jul 2006 First Online: 02 Mar 2017 Online ISSN: 2368-0261 Print ISSN: 0007-4802 © The Society of Canadian Petroleum Geologists Bulletin of Canadian Petroleum Geology (2006) 54 (3): 273–291. https://doi.org/10.2113/gscpgbull.54.3.273 Article history Received: 30 Sep 2005 Accepted: 06 Jul 2006 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Charles E. Barker, Todd Dallegge; Secondary gas emissions during coal desorption, Marathon Grassim Oskolkoff-1 Well, Cook Inlet Basin, Alaska: implications for resource assessment. Bulletin of Canadian Petroleum Geology 2006;; 54 (3): 273–291. doi: https://doi.org/10.2113/gscpgbull.54.3.273 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract Cuttings samples of sub-bituminous humic coals from the Oligocene to Pliocene Tyonek Formation, Cook Inlet Basin, Alaska show secondary gas emissions whose geochemistry is consistent with renewed microbial methanogenesis during canister desorption. The renewed methanogenesis was noted after initial desorption measurements had ceased and a canister had an air and desorbed gas mixture backflow into the canister during a measurement. About a week after this event, a secondary emission of gas began and continued for over two years. The desorbed gas volume reached a new maximum, increasing the total from 3.3 to 4.9 litres, some 48% above the pre-contamination total volume.The gases released during desorption show a shift in the isotopic signature over time of methane from δ13CCH4 of −53.60 ‰ and δDCH4 of −312.60 ‰ at the first day to δ13CCH4 of −57.06 ‰ and δDCH4 of −375.80 ‰ after 809 days, when the experiment was arbitrarily stopped and the canister opened to study the coal. These isotopic data, interpreted using a Bernard Diagram, indicate a shift from a mixed thermogenic and biogenic source typical of natural gases in the coals and conventional gas reservoirs of the Cook Inlet Basin to a likely biogenic acetate-fermentation methane source. However, the appearance of CO2 during the renewed gas emissions with a δ13CCO2 of +26.08 to +21.72 ‰, interpreted using the carbon isotope fractions found for acetate fermentation and CO2 reduction between CO2 and CH4 by Jenden and Kaplan (1986), indicates a biogenic CO2-reduction pathway may also be operative during renewed gas emission.Adding nutrients to the coal cuttings and canister water and culturing the microbial consortia under anaerobic conditions led to additional methane-rich gas generation in the laboratory. After this anaerobic culturing, ultraviolet microscopy showed that canister water contained common, fluorescent, rod-like microbes comparable to Methanobacterium sp. Scanning electron microscope investigations of the coal matrix showed several morphological types of microbes, including rod, cocci and spherical forms attached to the coal surface. These microbes apparently represent at least a portion of the microbial consortia needed to depolymerize coal, as well as to generate the observed secondary methane emission from the canister.The introduction of 48% more methane from secondary sources has a major impact on coal-bed methane resource assessments and also in determining the true, in-situ degree of methane saturation in coal-beds using isotherms. Canister and isotherm measurements that show “supersaturation” of methane may actually be the result of additional gases generated during secondary methanogenesis. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.