Main Conditions for Formation of Middle-large Gas Fields and the Potential Gas Exploration Areas in China

Chinese natural gas industry has stepped into a rapidly developing stage since 1990s. High increasing of proved gas reserves and gas production depends on the discovery of middle-large gas fields. The proved gas reserve of middle-large gas fields which is above 100 × 108 m3 accounts for 89% of all the cumulative proved reserves. On the basis of great exploration progress achieved in recent years, the four main factors controlling the formation of middle-large gas fields are put forward: (1) coal derived gas and oil type gas are the two main genetic gas types in China, and coal measures and high to over matured marine source rocks control the gas generation; (2) widely distributed pore-type reservoirs are the main reservoirs of middle-large gas fields, which include large fluvial delta sandstone, reef flat carbonate, weathered crust carbonate, corroded dolomite, volcanic rocks, etc.; (3) coal measures and evaporate are main seal rocks controlling gas preservation; (4) large structural traps in foreland basins, and wide-area subtle traps in craton basins and rift basins control the gas accumulation in middle-large gas fields. The potential gas exploration fields include foreland basins, carbonate and subtle traps in craton basins, and deep reservoirs in rift basins in East China, East China Sea and South China Sea.