琼东南盆地崖南凹陷西缘发育有我国最大的海上气田―― YA13 -1气田。而位于同一凹陷东南缘的 YA2 1 -1构造的天然气成藏条件欠佳 ,近年在该构造所钻探的几口井均未获得突破。从烃源条件、储层条件和能量场配置等 3个方面探讨了无突破的原因。 YA1 3 -1气田天然气主要来自于琼东南盆地的崖南凹陷 ,且可能有莺歌海盆地埋深分别大于 445 0 m和 470 0 m的崖城和陵水组烃源岩的贡献。YA2 1 -1构造的主要源岩可能为乐东凹陷 ,其浅海 A型源岩和浅海 B型源岩的发育条件均很差。据沉积相的研究 ,YA2 1 -1构造的陵水组为滨海相沉积 ,相对于 YA1 3 -1气田储层来说 ,粒度变细 ,且以细砂岩为主。YA1 3 -1构造和 YA2 1 -1构造的能量场配置和流体活动也有明显的不同。YA1 3 -1构造盖层发育超压 ,储层为常压并为侧向流体充注体系 ,属于所谓的“黄金配置”能量场。而 YA2 1 -1构造储层和盖层均发育超压 ,且盖层被压裂 ,属垂向流体泄放体系。总之 ,YA2 1 -1构造具有烃源条件差、储层条件差、区域能量配置条件差“三差”特点 ,故难以形成大气田。

 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.