琼东南盆地深水区中央峡谷天然气成藏条件与成藏模式

Accumulation Condition and Model of Gas Reservoir in Central Caynon in Deepwater Area of Northern South China Sea

利用钻井岩芯、岩屑地质化验资料及测井、二维、三维地震数据,综合分析了琼东南盆地深水区中央峡谷储层的发育特征、天然气成藏条件及成藏主控因素。结果表明,峡谷中、下部堆积的多期浊积砂岩,储集物性好,是该区带的优质储层;峡谷内发育的大量岩性、构造-岩性复合型圈闭为天然气聚集造就了重要场所;凹陷中的渐新统崖城组煤系烃源岩及广厚的半封闭浅海泥岩生气潜力大,提供了丰富的烃源基础;峡谷下方的底辟/微裂隙是深部崖城组烃源岩生成的天然气向上运移的重要通道。可见,中央峡谷成藏条件优越,圈闭有效性和运移是该区天然气成藏的关键要素;由于峡谷内圈闭大多数定型于上新世莺歌海组沉积时期,与下伏崖城组烃源岩主生气期形成合理配置,因此,天然气成藏较晚,L1、L2和L3气田的重大发现就是很好的例证。

In order to analyze the gas reservoirs and main controlling factors of the central canyon reservoir in Qongdongnan Basin deep water area, we employed well cores, cuttings, logging, natural gas data and two- dimensional, three-dimensional seismic data. The results show that multi period turbidities sandstone accumulated in the middle of or bottom of the canyon have good reservoir quality, and are the high quality reservoir of the area. Lithological traps and structural stratigraphic traps developed in the canyon created an important place for natural gas. Oligocene Yacheng Formation source rocks and semi-enclosed shallow mudstone are of great potential for gas, and provide a rich hydrocarbon source. A diapir or micro fissures below the canyon is an important migration channel for deep natural gas. Altogether, the central canyon has good reserves accumulation condition; migration and trapping is key elements for gas accumulation in this area. Most traps formed during the Yinggehai Formation Pliocene sedimentary period, and reasonably coupled with the underlying Yacheng source rocks. Therefore, natural gas accumulated at late stage, which have been confirmed by the important discovery of gas field L1 /L2 and L3.