PetroChina, Research Institute of Petroleum Exploration and Development, China

In order to study the genesis of gas sources in gas hydrate discoveries and areas of gas hydrate potential, the amounts of gas generated in 58 sediment samples from 4 sites of ODP Expedition 204 have been modeled by 5 temperature points, and gas chromatography was used to test the isotopes from different temperature points. The test results show that methane carbon isotope (delta (super 13) C) is evidently heavier among the lower temperature modeling points, commonly more than -40 ppm, displaying the isotopic features of thermogenic gas; while the lighter delta (super 13) C could reach -75.5 ppm when the modeling temperature is above 55 degrees C, showing the isotopic features of biogenic gas. Integrated with a discussion of gas genesis in the Dongsha potential area, it is concluded that gas genesis could be controlled by many factors, and correct gas genesis could be determined through a combination of other factors besides methane carbon isotopes.