麻江古油藏周缘露头层序地层与南方海相油气藏保存条件

Outcrop Sequence Stratigraphy of the Majiang Ancient Oil Reservoir and Its Suggestion to the Study on the Sealing Capability of the Marine Oil Field Developed in the South China

中国南方发育了巨厚的碳酸盐岩,由于经历了多起构造活动、多期生排烃和多幕次的油气充注和破坏,油气的保存条件是决定现今南方是否存在具有经济价值的油气藏的关键。通过对麻江古油气藏周缘野外露头层序地层学分析,识别出3种不同背景条件控制下发育的层序:即缓坡型(无明显坡折)、生长断层型和陆架坡折型。通过考察层序地层与油气显示的关系,发现主要的油气显示(沥青脉)多赋存于海泛体系域直接覆盖的低位体系域或下伏层序的高位体系域中,充分说明海泛体系域是南方海相油气藏最主要的盖层。暗示南方海相油气藏勘探应重视区域性和全球性的海泛面所形成的区域盖层对油气藏的保存作用,局部海泛所形成的局部盖层不足以使油气藏在多期构造反转和抬升剥蚀中免于破坏。同时应加强构造活动中不同层序发育模式中不同体系域保存条件的差异性分析,采用不同的油气勘探战略。

Multi-episodic tectonic movement accompanied by multi-episodic hydrocarbon generation and hydrocarbon recharging and destroying makes the sealing capacity the key factor that control whether or not it is possible to find profitable oil and/or gas pool in the thick marine carbonate sequences developed in the South China. Outcrop sequence stratigraphic study around the ancient Maji^ing oil field indicate that there exist three kinds of sequences developed under the growth faults, the slope of the continental shelf and the mild ramp respectively. The hydrocarbon show is found mainly in the low-stand system tracts （LST） and the high-stand system tracts （HST） of the underlying sequence directly under the cover of the transgression system tracts （TST） developed in the upper sequence. The transgressive system tract in a sequence is the main cap rock of the ancient oil reservoir suggests that hydrocarbon exploration in the South china should emphasize the sealing effect of TST developed under the regional and the global sea- flooding, while the TST developed under the local sea- flooding may not enable the oil/gas pool survive multi-episodic tectonic movement. The difference of the hydrocarbon abundance in different types of sequences developed in the Majiang ancient oil reservoir enlighten that the sequence model developed in the marine carbonate should be systematically studied and then evaluate the sealing difference of the three system tracts.