Space-time distribution of gas field in China

There are 321 gas fields in total in the continent and offshore areas in China, among which there are 252 small fields, 54 middle ones, 15 large ones. Although the number of small fields is 79% in total, their proved reserves is only 16% in the total proved geologic reserves in China; while the number of middle and large fields are 21% in total, but their proved reserves are 84 % in total. Only in the large fields does the proved reserves occupy one half of the total ones of natural gas. All the data from statistics show that middle and large gas fields have been the essential parts of the proved reserves in China. In the middle and large gas fields, there appears many kinds of gases, like coal-formed gas, shale gas and carbonate gas. The proved reserves of coal-formed gas occupies 57% in total proved reserves of large and middle gas fields. Gas fields have been found to be distributed mainly in Cenozoic, Upper Palaeozoic and Lower Palaeozoic. The proved reserves in Cenozoic, Mesozoic, Upper Palaeozoic, Lower Palaeozoic, Proterozoic respectively are 38%, 17%, 30%, 13% and 2% in total. The proved reserves from the most to the least were found in successive geologic formations as follows: Tertiary, Carboniferous, Ordovician, Triassic, Quaternary, Crataceous, Permian, Jurassic and Sinian. But till now the proved reserves of gas have not been found in Devonian, Silurian and Cambrian. Among those discovered large and middle gas fields in China, gases in reservoirs were found from various gas sources. There are a large number of coal-formed gas there. Most post-matured cracking gas is distributed in Sichuan, Talimu and E' erduosi Basins. Most associated gas is gathered in Songliao Basin, Bohai Bay and Zhunge'er Basin. Mantle source inorganic gas of carbon dioxide is distributed in the eastern heat basins with the thinner crust thickness.