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Title: Evidence for bacterially generated hydrocarbon gas in Canadian shield and Fennoscandian shield rocks

Abstract

Hydrocarbon-rich gases found in crystalline rocks on the Canadian and Fennoscandian shields are isotopically and compositionally similar, suggesting that such gases are a characteristic feature of Precambrian Shields rocks. Gases occur in association with saline groundwaters and brines in pressurized [open quotes]pockets[close quotes] formed by sealed fracture systems within the host rocks. When released by drilling activities, gas pressures as high as 5000 kPa have been recorded. Typical gas flow rates for individual boreholes range from 0.25 L/min to 4 L/min. The highest concentrations of CH[sub 4] are found in the deepest levels of the boreholes associated with Ca-Na-Cl (and Na-Ca-Cl) brines. N[sub 2] is the second major component of the gases and with CH[sub 4] accounts for up to 80 to >90 vol%. Higher hydrocarbon (C[sup +][sub 2]) concentrations range from <1 to 10 vol%, with Cl/(C2 + C3) ratios from 10-1000. Isotopically the gases show a wide range of values overall ([delta][sup 13]C = -57.5 to -41.1%; [delta]D = -245 to -470%) but a relatively tight cluster of values within each sampling locality. The Enonkoski Mine methanes are unique with [delta][sup 13]C values between -65.4 and -67.3% and [delta]D values between -297 and -347%. The shield gases aremore » not readily reconcilable with conventional theories of methanogenesis. The range of C1/(C2 + C3) ratios for the shield gases is too low to be consistent with an entirely bacterial origin. In addition, [delta]D[sub CH4] values are in general too depleted in the heavy isotope to be produced by thermogenic methanogenesis or by secondary alteration processes such as bacterial oxidation or migration. However, isotopic and compositional evidence indicates that bacterially derived gas can account for a significant component of the gas at all shield sites.« less

Authors:
;  [1];  [2];  [3];  [4]; ;  [5]
  1. Univ. of Waterloo, Ontario (Canada)
  2. UFZ, Umweltforschungszentrum, Leipzig-Halle (Germany)
  3. Univ. of Virginia, Charlottesville, VA (United States)
  4. Idaho State Univ., Pacatello, ID (United States)
  5. Geological Survey of Finland, Espoo (Finland)
Publication Date:
OSTI Identifier:
5207885
Resource Type:
Journal Article
Journal Name:
Geochimica et Cosmochimica Acta; (United States)
Additional Journal Information:
Journal Volume: 57:23-24; Journal ID: ISSN 0016-7037
Country of Publication:
United States
Language:
English
Subject:
03 NATURAL GAS; GASES; BIOSYNTHESIS; HYDROCARBONS; IGNEOUS ROCKS; ISOTOPE RATIO; METAMORPHIC ROCKS; METHANE; METHANOGENIC BACTERIA; MICROORGANISMS; ALKANES; BACTERIA; FLUIDS; ORGANIC COMPOUNDS; ROCKS; SYNTHESIS; 030200* - Natural Gas- Reserves, Geology, & Exploration

Citation Formats

Lollar, B S, Frape, S K, Fritz, P, Macko, S A, Welhan, J A, Blomqvist, R, and Lahermo, P W. Evidence for bacterially generated hydrocarbon gas in Canadian shield and Fennoscandian shield rocks. United States: N. p., 1993. Web. doi:10.1016/0016-7037(93)90609-Z.
Lollar, B S, Frape, S K, Fritz, P, Macko, S A, Welhan, J A, Blomqvist, R, & Lahermo, P W. Evidence for bacterially generated hydrocarbon gas in Canadian shield and Fennoscandian shield rocks. United States. doi:10.1016/0016-7037(93)90609-Z.
Lollar, B S, Frape, S K, Fritz, P, Macko, S A, Welhan, J A, Blomqvist, R, and Lahermo, P W. Wed . "Evidence for bacterially generated hydrocarbon gas in Canadian shield and Fennoscandian shield rocks". United States. doi:10.1016/0016-7037(93)90609-Z.
@article{osti_5207885,
title = {Evidence for bacterially generated hydrocarbon gas in Canadian shield and Fennoscandian shield rocks},
author = {Lollar, B S and Frape, S K and Fritz, P and Macko, S A and Welhan, J A and Blomqvist, R and Lahermo, P W},
abstractNote = {Hydrocarbon-rich gases found in crystalline rocks on the Canadian and Fennoscandian shields are isotopically and compositionally similar, suggesting that such gases are a characteristic feature of Precambrian Shields rocks. Gases occur in association with saline groundwaters and brines in pressurized [open quotes]pockets[close quotes] formed by sealed fracture systems within the host rocks. When released by drilling activities, gas pressures as high as 5000 kPa have been recorded. Typical gas flow rates for individual boreholes range from 0.25 L/min to 4 L/min. The highest concentrations of CH[sub 4] are found in the deepest levels of the boreholes associated with Ca-Na-Cl (and Na-Ca-Cl) brines. N[sub 2] is the second major component of the gases and with CH[sub 4] accounts for up to 80 to >90 vol%. Higher hydrocarbon (C[sup +][sub 2]) concentrations range from <1 to 10 vol%, with Cl/(C2 + C3) ratios from 10-1000. Isotopically the gases show a wide range of values overall ([delta][sup 13]C = -57.5 to -41.1%; [delta]D = -245 to -470%) but a relatively tight cluster of values within each sampling locality. The Enonkoski Mine methanes are unique with [delta][sup 13]C values between -65.4 and -67.3% and [delta]D values between -297 and -347%. The shield gases are not readily reconcilable with conventional theories of methanogenesis. The range of C1/(C2 + C3) ratios for the shield gases is too low to be consistent with an entirely bacterial origin. In addition, [delta]D[sub CH4] values are in general too depleted in the heavy isotope to be produced by thermogenic methanogenesis or by secondary alteration processes such as bacterial oxidation or migration. However, isotopic and compositional evidence indicates that bacterially derived gas can account for a significant component of the gas at all shield sites.},
doi = {10.1016/0016-7037(93)90609-Z},
journal = {Geochimica et Cosmochimica Acta; (United States)},
issn = {0016-7037},
number = ,
volume = 57:23-24,
place = {United States},
year = {1993},
month = {12}
}