渤海湾盆地海域深层——超深层大型复合潜山油气藏形成条件

Formation conditions of deep to ultra-deep large composite buried-hill hydrocarbon reservoirs in offshore Bohai Bay Basin,China

基于三维地震、钻井、井壁取心、薄片和分析化验资料,通过渤海湾盆地海域中—新生界大地构造动力学分析、潜山储层研究和潜山油气差异富集规律分析,结合典型油气藏解剖,系统总结深层—超深层复合潜山大型油气田成山、成储和成藏的必要条件,并建立复合潜山油气差异富集模式。研究表明:①华北克拉通经历的燕山期和喜马拉雅期双幕破坏是渤海湾盆地海域深层—超深层复合潜山发育的主要构造动力,受华北克拉通破坏和郯庐断裂活动的联合控制,破坏中心由渤海湾盆地周缘向渤中凹陷幕式迁移、收敛,渤海湾盆地海域有序成山,进而形成了渤中凹陷中环带和内环带两个复合潜山的发育区带;②受华北克拉通双幕破坏的控制,渤中凹陷中环带和内环带是风化壳下伏流体溶-缝带储层形成的有利区域;③克拉通破坏Ⅱ幕,中环带和内环带剧烈沉降,巨量生烃产生超压,并向复合潜山充注成藏,复合潜山低部位和内幕仍具较好的成藏条件。研究成果推动潜山勘探转向复合潜山立体勘探,同时指出渤中凹陷中环带深层—超深层复合潜山内幕勘探和凹陷内环带复合潜山多期火山机构勘探是渤海下步勘探的重要接替领域。

Based on the data of 3D seismic survey,drilling,sidewall coring,thin sections and tests,this paper systematically discusses the necessary conditions for the formation of buried-hills and reservoirs,and accumulations in the large oil and gas fields in deep to ultra-deep composite buried hills in the Bohai Sea through the analysis of the Meso-Cenozoic geotectonic dynamics,buried-hill reservoir characteristics,and differential enrichment patterns of oil and gas in the buried hills,as well as case study of typical reservoirs.The key findings are as follows.First,the double-episode destruction of the North China Craton in the Yanshanian and Himalayan served as the primary tectonic driver for the development of deep to ultra-deep composite buried hills in the offshore Bohai Bay Basin.Jointly controlled by the destruction of the North China Craton and the activity of the Tanlu Fault,the destruction center migrated and converged episodically from the margins of the Bohai Bay Basin towards the Bozhong Sag,resulting in an orderly mountain-building process within the offshore Bohai Bay Basin and subsequently two development zones for composite buried hills,i.e.the middle and inner rim zones within the Bozhong Sag.Second,under the coupling of favorable lithologies and multi-stage structures,the middle and inner rim zones are conducive to the formation of reservoirs in fluid dissolution–pore/fracture zones underlying the weathering crust.Third,during the Episode II craton destruction,the middle and inner rim zones subsided intensely,along which massive hydrocarbons were generated,resulting in the overpressure,and then migrated to and accumulated in the composite buried hills.The lower parts and interiors of these buried hills still possess excellent conditions for hydrocarbon accumulation.These findings promote a shift in buried hill exploration to three-dimensional exploration of composite buried hills.It is emphasized that the deep to ultra-deep composite buried hill interiors in the middle rim zone and the multi-stage volcanic edifices in the inner rim zone of the sag represent important successor areas for future exploration in the Bohai Sea.