中国近海前第三纪残余盆地及其勘探潜力与方向

Petroleum potential and exploration direction of pre-Tertiary remnant basins in Offshore China

中国近海前第三纪残余盆地主要分布于渤海、北黄海、南黄海、东海和南海北部海域 ,尚保存有效烃源岩的残余盆地分布面积近 36× 10 4 km2 ,涉及古生界和中生界两大勘探领域 ,具有盆地类型多样、成盆背景复杂、构造改造强烈的特点。中国近海前第三纪残余盆地存在古生界和中生界两套烃源层系 ,其中南海北部和东海发育T3(?)—J1+ 2 烃源岩 ,南黄海和渤海主要发育C—P烃源岩 ,北黄海发育J3—K1烃源岩。利用地震、重磁和钻井资料 ,参考海域周边区域地质资料和陆区具相同或相似构造背景盆地前第三系油气田资料 ,对中国近海前第三纪残余盆地的主要类型、原型盆地演化特征、关键石油地质条件以及油气勘探潜力等进行了分析。中国近海前第三纪残余盆地普遍经历了多期生排烃过程 ,保存条件是制约其油气发现和勘探潜力的关键。中国近海前第三纪残余盆地“自生自储”型油气藏勘探开发风险整体较大 ,但如果立足“多源兼找、立体勘探”的指导思想 ,那么仍然存在一些值得探索的领域 :①以中生界“自生自储”型油气藏为主的探区———潮汕盆地和南黄海北部盆地 ;②以“新生古储”或“新生中储”型油气藏为主的探区———渤海和东海天台 钓北斜坡带。南黄海勿南沙隆起古生界原生油气藏的勘探 。

In China, pre-Tertiary offshore remnant basins mainly exist in Bohai Bay, the northern Yellow Sea, the southern Yellow Sea, East China Sea and the northern South China Sea. These basins are nearly 36×10 4km 2 in effective source-rock distribution, have two major exploration domains(Paleozoic and Mesozoic), and are characterized by multiple basin types, complex basin-forming background and extensive tectonic reworking. There are two sets of source rocks, i.e.Paleozoic and Mesozoic source rock, in these basins, with T 3(?)—J 1+2 source rocks developed in the northern South China Sea and East China Sea, C—P source rocks in Bohai Bay and the southern Yellow Sea, and J 3—K 1 source rocks in the northern Yellow Sea. In combination with the regional geological data and the information from onshore pre-Tertiary oil & gas fields with similar tectonic setting, the offshore data of seismic, gravity-magnetic and drilling have been used to analyze main types, proto-basin evolution, key conditions of petroleum geology and exploration potential for these pre-Tertiary basins. These basins have experienced several periods of hydrocarbon generation and expulsion, and the key factor to control hydrocarbon discovery and exploration potential is preservation. The overall risk of exploration and development is quite high for the hydrocarbon accumulations of “self-source and self-reservoir” type in these basins, but some domains are still worth further exploration, given a guidance of “searching for all sources and prospecting stereoscopically”: (1) the Mesozoic domain dominated by the “self-source and self-reservoir” type of accumulations, including Chaoshan basin and the northern South Yellow Sea; (2) the domain dominated by the “Ceno-source and Paleo-reservoir” or“ Ceno-source and Meso-reservoir” types of accumulations, such as Bohai Bay and Tiantai—Diaobei slope in East China Sea. For the primary Paleozoic hydrocarbon accumulations on Wunansha uplift of the southern Yellow Sea, exploration should be focused on low relief anticlines with better seals, well-preserved traps and lower late faulting, which are in the core of a duplex synclinorium belt developed during early Mesozoic.