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Geosciences 2017, 7(2), 35;

Evaluation of Near-Surface Gases in Marine Sediments to Assess Subsurface Petroleum Gas Generation and Entrapment

Energy Futures Lab, Imperial College London, London SW7 2AZ, UK
Academic Editors: Alexei V. Milkov, Giuseppe Etiope and Jesus Martinez-Frias
Received: 30 December 2016 / Revised: 27 March 2017 / Accepted: 10 April 2017 / Published: 4 May 2017
(This article belongs to the Special Issue Natural Gas Origin, Migration, Alteration and Seepage)
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Gases contained within near-surface marine sediments can be derived from multiple sources: shallow microbial activity, thermal cracking of organic matter and inorganic materials, or magmatic-mantle degassing. Each origin will display a distinctive hydrocarbon and non-hydrocarbon composition as well as compound-specific isotope signature and thus the interpretation of origin should be relatively straightforward. Unfortunately, this is not always the case due to in situ microbial alteration, non-equilibrium phase partitioning, mixing, and fractionation related to the gas extraction method. Sediment gases can reside in the interstitial spaces, bound to mineral or organic surfaces and/or entrapped in carbonate inclusions. The interstitial sediment gases are contained within the sediment pore space, either dissolved in the pore waters (solute) or as free (vapour) gas. The bound gases are believed to be attached to organic and/or mineral surfaces, entrapped in structured water or entrapped in authigenic carbonate inclusions. The purpose of this paper is to provide a review of the gas types found within shallow marine sediments and examine issues related to gas sampling and extraction. In addition, the paper will discuss how to recognise mixing, alteration and fractionation issues to best interpret the seabed geochemical results and determine gas origin to assess subsurface petroleum gas generation and entrapment. View Full-Text
Keywords: surface geochemistry; sediment gases; seabed gases surface geochemistry; sediment gases; seabed gases

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Abrams, M.A. Evaluation of Near-Surface Gases in Marine Sediments to Assess Subsurface Petroleum Gas Generation and Entrapment. Geosciences 2017, 7, 35.

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