Abstract: The genesis of carbon dioxide and the geological characteristics of carbon dioxide infilling and oil displacement in the northern marginal basin of the South China Sea were investigated using a lot of geological and geochemical data.The results show that the genesis of carbon dioxide includes four types of chemical genesis of crust-source rock,crust-source organic genesis,crust-mental mixed source type and volcano-source genesis in the northern marginal basins of the South China Sea.Formation of crust-source and crust-mental mixed source carbon dioxide reservoir in the Yinggehai Basin was mainly controlled by the physical-chemical action of hot fluid in mud diapir with multiple expulsion and the marine calcareous sandstone and mudstone in Pliocene-Miocene age.The volcano-source and mantle-source carbon dioxide reservoirs in the Qiongdongnan Basin and the Pearl River Mouth Basin were mainly controlled by the volcanic activities and the existence of associated discordogenic faults connected to the mantle.The carbon dioxide infilling and oil displacement in the generation of reservoir were controlled by many geologic factors such as migration condition and supply of carbon dioxide.Because the carbon dioxide infilling and oil displacement easily lead to redistribution of oil and gas in the reservoir and change the appearance features of reservoir,a new oil or gas reservoir or hydrocarbon reservoir is often formed.So the characters of carbon dioxide infilling and oil displacement can be treated as a mark for recognizing the forming process of oil and gas reservoirs and used to predict oil and gas migration and accumulation and to trace oil and gas distribution features.

Key words: northern South China Sea, marginal basin, carbon dioxide reservoir, carbon dioxide genesis, carbon dioxide infilling and oil displacement, hydrocarbon reservoir, hydrocarbon distribution

摘要： 在获取大量地质、地球化学资料的基础上,对南海北部边缘盆地CO₂的成因及充注驱油特征进行了分析,结果表明:南海北部边缘盆地CO₂可划分为壳源型岩石化学成因、壳源型有机成因、壳幔混合型及火山幔源型成因4种成因类型;其中,莺歌海盆地壳源型及壳幔混合型CO₂运聚成藏主要受控于泥底辟热流体晚期分层分块多期局部上侵活动与上新统—中新统海相含钙砂泥岩的物理化学综合作用;琼东南盆地东部及珠江口盆地火山幔源型CO₂成藏主要受控于幔源型火山活动及沟通深部气源的基底深大断裂的展布;CO₂运聚成藏中,其充注驱油过程主要受运聚输导条件及气源供给等诸多地质关键因素的制约和控制.由于CO₂充注驱替往往导致油气藏中油气再分配或重新组合,并引起原来的油气产出及产状特征发生变化,故容易形成新的油藏或气藏.因此,可以将CO₂充注驱油特征作为判识油气成藏动态过程的示踪标志,用于预测油气运聚状态,追踪油气分布特征.

关键词: 南海北部, 大陆边缘盆地, 二氧化碳气藏, 二氧化碳成因, 二氧化碳充注驱油, 油气成藏, 油气分布