南海西部中建南盆地烃源岩热演化史

Thermal evolution history of hydrocarbon source rock in the Zhongjiannan Basin,western South China Sea

中建南盆地勘探程度较低,对盆地内油气资源前景尚无明确认识。利用PetroMod盆地模拟软件,对盆地内烃源岩热演化史进行了模拟。结果表明:中建南盆地内最主要的一套烃源岩为始新世早—中期烃源岩,生烃门限为2050~2125 m,但盆地内2个主要生烃坳陷——中部坳陷和北部坳陷内的始新世早—中期烃源岩热演化程度差别较大,分别在32、24 Ma开始进入生烃门限。现今中建南盆地中部坳陷的热演化程度高于北部坳陷,因此中部坳陷的生烃潜力应大于北部坳陷。中建南盆地主力烃源岩尽管在晚渐新世末陆续成熟,并进入生、排烃高峰期,但因缺少良好的区域性盖层,直至上新世末圈闭定型,油气才开始聚集成藏。因此,中建南盆地油气成藏的关键时期为上新世末。

The Zhongjiannan Basin is still in the early stage of exploration;its prospect of oil and gas isn′t understood clearly.The thermal evolution history of source rocks in the basin was simulated using PetroMod software.The main conclusions are as follows:the most important set of hydrocarbon source rocks in the Zhongjiannan Basin was the early-Eocene-middle-Eocene source rocks.The oil threshold is about at 2050-2125 m.But the thermal evolution degree of the source rocks in the central depression and the northern depression is different,the main source rocks reached the threshold of oil generation at 32 Ma and 24 Ma respectively.Nowadays,the thermal evolution degree of the source rocks in the central depression is higher than that of the northern depression.Therefore,the hydrocarbon generation potential of the central depression is better than that of the northern depression.Though the main source rocks were matured from the end of late Oligocene and afterwards entered the peak stage of hydrocarbon generation and expulsion,the hydrocarbon began to accumulate into reservoirs until the end of Pliocene,due to the lack of good regional caprocks.Thus,the crucial time of hydrocarbon accumulation was at the end of Pliocene.