Main factors controlling the foundation of medium-giant gas fields in China

Medium-giant gas fields refer to those whose proved reserves are or more than 10 × 109 m3. Now, 30 such fields have been found in China. The main controlling factors of their formation are as follows:gas-generating center and its surroundings; traps related to paleo-uplift in the gas-generating area; traps of medium-giant size hidden in low-medium rank coal-bearing series and those above or beneath the coal measures; late reservoir formation; poretype reservoir in gas-generating area and well-developed regional cap rock.