Hydrocarbon test in lower-layer atmosphere to predict deep-sea petroleum or hydrate in the Okinawa Trough: an example

Light hydrocarbon (methane, ethane, propane, butane and CO 2 ) test and C isotopic analysis of CO 2 are conducted for over 100 lower-layer atmospheric samples from the East China Sea slope and the Okinawa Trough. The results show that the lower-layer atmosphere mainly consists of CO 2 and then of CH 4 , and the CO 2 concentrations are calculated to have a high average value of 0.87 ω/10 -2 , about three times that of the regional background (0.3 ω/10 -2 ). The result also shows that the average value of C isotope - 20.8 × 10 -3 is given to the CO 2 , inferring that it is inorganic gas. Thus, for the future 's work in the Okinawa Trough, special attention should be paid to CO 2 hydrate, which is very possibly an important hydrate type.