Data Report: Molecular and Isotopic Compositions of the Extracted Gas from China’s First Offshore Natural Gas Hydrate Production Test in South China Sea

Three hundred gas samples recovered from SHSC-4 during China's first gas hydrate production test in the South China Sea were examined for gas component and isotopic composition. According to the gas chromatography analysis, all the gas samples from SHSC-4 are predominated by CH4, with minor N-2 + O-2, as well as trace amounts of CO2, C2H6, and C3H8. No H2S was detected. The molecular and isotopic data of the gas samples fall into the region of mixed origin on the plot of C-1/(C-2 + C-3) - C-13(1), which is close to the microbial origin. The discrimination diagram of C-13(1) - D-CH4 shows that the methane in all of the samples is of microbial origin, and is derived from the CO2 reduction.