Publication Date:
2017-04-04
Description:
Drylands are considered a net sink for atmospheric methane and a main item of the global inventories of the
greenhouse gas budget. It is outlined here, however, that a significant portion of drylands occur over
sedimentary basins hosting natural gas and oil reservoirs, where gas migration to the surface takes place,
producing positive fluxes of methane into the atmosphere. New field surveys, in different hydrocarbonprone
basins, confirm that microseepage, enhanced by faults and fractures in the rocks, overcomes the
methanotrophic consumption occurring in dry soil throughout large areas, especially in the winter season.
Fluxes of a few units to some tens of mg m−2 day−1 are frequent over oil–gas fields, whose global extent is
estimated at 3.5–4.2 million km2; higher fluxes (〉50 mg m−2 day−1) are primarily, but not exclusively,
found in basins characterized by macro-seeps. Microseepage may however potentially exist over a wider
area (∼8 million km2, i.e. 15% of global drylands), including the Total Petroleum Systems, coal measures and
portions of sedimentary basins that have experienced thermogenesis. Based on a relatively large and
geographically dispersed data-set (563 measurements) from different hydrocarbon-prone basins in USA and
Europe, upscaling suggests that global microseepage emission exceeding 10 Tg year−1 is very likely.
Microseepage is then only one component of a wider class of geological sources, including mud volcanoes,
seeps, geothermal and marine seepage, which cannot be ignored in the atmospheric methane budget.
Description:
Published
Description:
265-274
Description:
4.5. Studi sul degassamento naturale e sui gas petroliferi
Description:
JCR Journal
Description:
restricted
Keywords:
microseepage
;
methane flux
;
soil sink
;
drylands
;
petroleum
;
greenhouse gas
;
04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
