Abstract:

 YA 13-1 gas field, the biggest offshore gas field in China, is located in the w est of Yanan depression.In the southeast, there lies YA 21-1 structure. In g eneral, YA 21-1 structure have “three poor” for gas accumulation, that is, so urce rock, reservoir and energy field. The natural gas of YA 13-1 gas field co mes from Yachen and Lingshui formation of Yinggehai and Qiongdongnan basin. How ever, the source rock of YA 21-1 comes from Ledong depression, that is the firs t poor.The reservoirs of YA 21-1 is worse than YA 13-1, that is the second poor. Regarding the energy fields, it shows that the caps rock and reservoirs ha ve over-pressure, that is the third poor.So, the source rock, reservoirs and  energy fields controlled the gas accumulation of YA 21-1 structure.

Key words: Yanan depression, YA 21-1 structure, YA 13-1 structure, Source rock, Reservoirs, Regional energy fields