莺歌海盆地中央底辟带油气成藏条件分析

莺歌海盆地位于海南岛以西、中南半岛以东的海域,总体呈NW-SE向。该盆地由中央底辟带和斜坡带两个构造单元组成。底辟带发育中新统(莺黄组、梅山组和三亚组)及渐新统(崖城组)两套烃源岩,生油门限深度在2800～3000m之间;主要圈闭由底辟流体上拱形成,底辟活动的幕式发育决定了油气幕式运移。不同的油气运移动力形成了不同类型的油气藏:中新统源岩在高温高压及欠压实作用下,形成高压囊,使上覆地层破裂,产生高角度断层和裂隙,烃类气沿此形成深部及浅部气藏;另外,本区深部的无机成因CO₂气在高压作用下,排驱断裂附近的烃类气,一方面对原有气藏进行破坏,另一方面在远离断裂的两翼形成含少量CO₂气体的新的烃类气藏。

ANALYSIS ON HYDROCARBON POOL-FORMING CONDITION OF CENTRAL DIAPIRIC ZONE IN YINGGEHAI SEA BASIN

Yinggehai Sea Basin is situated in the west of Hainan Island and the east of Zhongnan Peninsula and stretches in NW-SE direction.The basin consists of central diapiric zone and a slope zone.Two sets of source rocks including Miocene Yinggehai,Huangliu,Meishan and Sanya Formations and Oligocene Yacheng Formation developed in the diapiric zone.Oil threshold is between 2 800～3 000 m depth.The traps were formed by the upward arch of diapiric fluid,and episodic diapir activity determined hydrocarbon episodic migration.Different migration dynamic forces resulted in different types of oil and gas pools:under high temperature,high pressure and uncompaction,the Miocene source rocks formed high pressure pocket which break overlying strata and formed deep and shallow gas pools;deep seated inorganic CO