珠江口盆地珠三坳陷古湖泊与油气

PALAEOLIMNOLOGY AND HYDROCARBON POTENTIAL IN ZHU Ⅲ DEPRESSION, PEARL RIVER MOUTH BASIN

珠江口盆地珠三坳陷发育早期为断陷湖泊发育期（古新世－早渐新世），勘探证实该时期是坳陷内主要烃源岩形成期，珠三坳陷古湖泊的演化经历了三个阶段。早期山间湖泊阶段，中期湖泊鼎盛阶段和晚期湖泊萎缩阶段，总体来说三个阶段的湖水性质为低矿化度，低CaCO3含量的淡水，但生物发育以及沉积物供给等条件有所不同，湖泊鼎盛阶段浮游藻类大量发育，水体的垂直分导使有机质得到保存，形成了本坳陷最好的生油岩，湖泊萎缩阶段大量陆源碎屑进入，广泛发育湖沼相沉积，形成了以煤系地层为主的气源岩，古湖泊不同阶段形成的两套烃源岩，决定了坳陷内存在两套油气体系。

The early stage of Zhu Ⅲ depression of the Pearl River Mouth Basin (Palaeocene-Early Oligocene)was the development stage of rift lakes,which has been proved by exploration to be the developing stage of main source rocks in the depression. The palaeo-lakes in Zhu Ⅲ depression experienced three evolution stages , i. e. early intermountain lake stage .middle lake flourishing stage and late lake regression stage. The lake water in three stages are generally characterized by fresh water with low salinity and low calcium carbonate content,but varied with organism and sediments source supply were different. At the lake flourishing stage,planktonic algae was largely developed and the organic matters were well preserved due to the water vertical stratification, thus the best oil source rocks in the depression were formed. At the lake regression stage, limnetic sediments were widely developed as result of the influx of large amount of terrigenous elastics which gas source rocks predominated by the two hydrocarbon source rocks developed at different evolution stages of palaeo-lakes resulted in the development of two oil/gas systems in the depression.