Publication Date:
2021-06-15
Description:
Twenty-two gas samples were collected in August 2012 in the area of Amik basin (Turkey). Two samples were
collected from gas seeps, one was a bubbling gas in a thermal spring, while the remaining were dissolved gases
from cold and thermal groundwaters (T 16-43 °C). All gases were analysed for their chemical composition (He, H2,
O2, N2, CH4 and CO2) and for their He isotopic composition. Dissolved gases were also analysed for the carbon
isotopic composition of the total dissolved carbon (TDC), while free gases also for their higher hydrocarbon (C1 –
C5) content and for D of H2 and CH4, 13C of CH4
Basing on their chemical composition, the gases can be roughly subdivided in three groups. Most of the dissolved
gases (16) belonging to the first group were collected from springs or shallow wells (〈 150 m depth). All these
samples contain mainly atmospheric gasses with very limited H2 (〈 80 ppm) and CH4 (1 – 2700 ppm) contents
and minor concentrations of CO2 (0.5 – 11.2 %). The isotopic composition of TDC evidences an almost organic
contribution. The only exception is represented by the CO2-richest sample where a small but significant mantle
contribution is found. Such contribution can also be evidenced in its 3He rich isotopic composition. Further three
samples of this group evidence a small mantle contribution. These samples were collected in the northern part
of the basin along the main tectonic structures delimiting the basin and close to areas with quaternary volcanic
activity.
A second group is composed by two dissolved gases collected from deep boreholes (〉 1200 m depth). Their
composition is typical of hydrocarbon reservoirs being very rich in CH4 (〉 78 %) and N2 (〉 13%). Also the water
composition is typical of saline connate waters (Cl- and B-rich, SO4-poor). C-isotopic composition of methane
( 13C -65% ) points to a biogenic origin while He-isotopic composition indicates a prevailing crustal signature
for one (R/Ra 0.16) of the sites and small mantle contribution for the other (R/Ra 0.98).
To the last group belong four gas samples taken at two sites within the ophiolitic basement that crops out west of
the basin. These gases have the characteristic composition of gas generated by low temperature serpentinisation
processes with high hydrogen (37 – 50 %) and methane (10 – 61 %) concentrations. While all gases show an
almost identical D-H2 of -750h those of one of the two sites display an isotopic composition of methane
( 13C -5h D -105% ) and a C1/[C2+C3] ( 100) ratio typical of abiogenic hydrocarbons and mantle-type
helium (R/Ra: 1.33), while those of the other site evidence a contribution of a crustal (thermogenic) component
( 13C-CH4 -30h D -325h C1/[C2+C3] 3000). Such crustal contribution is also supported by higher
N2 contents (40% instead of 2%) and lower He-isotopic composition (R/Ra 0.07).
The preliminary results highlight contributions of mantle-derived volatiles to the fluids vented along the Amik
Basin. The main tectonic structure of the area, the Death Sea Fault, and other parallel structures crossing the basin
seem to be the responsible for deep-originated volatiles drainage towards shallow levels.
Description:
Submitted
Description:
Vienna, Austria
Description:
4.5. Studi sul degassamento naturale e sui gas petroliferi
Description:
open
Keywords:
gas geochemistry
;
water chemistry
;
stable isotopes
;
03. Hydrosphere::03.04. Chemical and biological::03.04.03. Chemistry of waters
;
03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
Conference paper
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