Geochemical characteristics of pore water in shallow sediments from north continental slope of South China Sea and their significance for natural gas hydrate occurrence

Abstract

Northern slope of the South China Sea is a potential area of gas hydrates and research focus areas. Analyzed geochemical parameters about pore water of the anions and cations of major components and δ 13 C DIC in the sediments from Shenhu sea area, Dongsha sea area and Southwest Taiwan Basin and collected by gravity piston. The results showed that Cl − concentration were no significant changes with depth at the three stations and their values were consistent with the normal sea water, SO 4 2- concentration showed significant changes in gradient descent from core top to bottom at three stations and Ca 2+ , Mg 2+ , Ca 2+ /Mg 2+ showed a similar downward trend with SO 4 2− concentration, but the amplitude is inconsistent. The SMI of Shenhu sea area, Dongsha sea area, Southwest Taiwan Basin were separately 11m, 8m, 6m and δ 13 C DIC of pore water in the sediments range from -10 ‰ to -27 ‰, which were similar with geochemistry characteristics of pore water in the sediments at other international regions of being found gas hydrate, such as Blake Ridge and Mexico Gulf. These geochemistry characteristics may suggest that natural gas hydrate reservoir released methane in deep sediments and methane was mixture gas as main causes of pyrolysis. Summary a series anomaly indicators and identification methods that use these geochemical anomalies characteristics about pore water of shallow sediments to trace gas hydrate in deep stratum.