Next Article in Journal
Next Article in Special Issue
Previous Article in Journal
Energies 2014, 7(6), 3886-3899; doi:10.3390/en7063886
Article

Gas Hydrate Occurrence Inferred from Dissolved Cl Concentrations and δ18O Values of Pore Water and Dissolved Sulfate in the Shallow Sediments of the Pockmark Field in Southwestern Xisha Uplift, Northern South China Sea

1,2
, 3
, 3
, 3
 and 1,3,*
Received: 19 February 2014; in revised form: 26 May 2014 / Accepted: 3 June 2014 / Published: 20 June 2014
(This article belongs to the Special Issue Coastal Ocean Natural Gas Hydrate 2014)
View Full-Text   |   Download PDF [832 KB, uploaded 20 June 2014]
Abstract: Deep-water pockmarks are frequently accompanied by the occurrence of massive gas hydrates in shallow sediments. A decline in pore-water Cl concentration and rise in δ18O value provide compelling evidence for the gas hydrate dissociation. Mega-pockmarks are widely scattered in the southwestern Xisha Uplift, northern South China Sea (SCS). Pore water collected from a gravity-core inside of a mega-pockmark exhibits a downward Cl concentration decrease concomitant with an increase in δ18O value at the interval of 5.7–6.7 mbsf. Concentrations of Cl, Na+, and K+ mainly cluster along the seawater freshening line without distinct Na+ enrichment and K+ depletion. Thus, we infer that the pore water anomalies of Cl concentrations and δ18O values are attributed to gas hydrate dissociation instead of clay mineral dehydration. Moreover, the lower δ18O values of sulfate in the target core (C14) than those in the reference core (C9) may be associated with the equilibrium oxygen fractionation during sulfate reduction between sulfate and the relatively 18O-depleted ambient water resulting from gas hydrate formation. The gas hydrate contents are estimated to be 6%–10% and 7%–15%, respectively, according to the offset of Cl concentrations and δ18O values from the baselines. This pockmark field in southwestern Xisha Uplift is likely to be a good prospective area for the occurrence of gas hydrate in shallow sediments.
Keywords: gas hydrate; pore water; chloride; δ18O; southwestern Xisha Uplift gas hydrate; pore water; chloride; δ18O; southwestern Xisha Uplift
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Export to BibTeX |
EndNote


MDPI and ACS Style

Luo, M.; Chen, L.; Tong, H.; Yan, W.; Chen, D. Gas Hydrate Occurrence Inferred from Dissolved Cl Concentrations and δ18O Values of Pore Water and Dissolved Sulfate in the Shallow Sediments of the Pockmark Field in Southwestern Xisha Uplift, Northern South China Sea. Energies 2014, 7, 3886-3899.

AMA Style

Luo M, Chen L, Tong H, Yan W, Chen D. Gas Hydrate Occurrence Inferred from Dissolved Cl Concentrations and δ18O Values of Pore Water and Dissolved Sulfate in the Shallow Sediments of the Pockmark Field in Southwestern Xisha Uplift, Northern South China Sea. Energies. 2014; 7(6):3886-3899.

Chicago/Turabian Style

Luo, Min; Chen, Linying; Tong, Hongpeng; Yan, Wen; Chen, Duofu. 2014. "Gas Hydrate Occurrence Inferred from Dissolved Cl Concentrations and δ18O Values of Pore Water and Dissolved Sulfate in the Shallow Sediments of the Pockmark Field in Southwestern Xisha Uplift, Northern South China Sea." Energies 7, no. 6: 3886-3899.


Energies EISSN 1996-1073 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert