琼东南盆地温压场特征及其与油气运聚的关系

CHARACTERISTICS OF GEOTHERM PRESSURE FIELD AND ITS RELATIONSHIP WITH HYDROCARBON MIGRATION AND ACCUMULATION IN QIONGDONGNAN BASIN,SOUTH CHINA SEA

琼东南盆地具有高温、高压特征。盆地平均地温梯度在4℃／100m以上，不同地带地温梯度存在明显差异，下第三系地温梯度明显低于上第三系，影响地温场的因素主要有火山活动，莫霍面埋深，断层活动和岩石性质，上、下第三系在构造背景，沉积环境等方面存在很大的差异，相应地划分为上、下两个超压系统，下超压系统主要由烃类的大量生成和裂解引起，强超压区分布在2号断裂带以南、上超压系统主要由欠压实作用引起，超超压区分布较局限，上、下超压系统的形成时间一致，均在中新世以后，琼东南盆地独特的温压场在很大程度上决定了区内油气的演化与分布。超压环境中存在3种成藏模式，下第三系勘探有3个最利区带和两个有利区带，上第三系勘探应重视盆地西北部的正常压力带，压力过渡带及东部浅层流体破裂较为发育地带。

Qiongdongnan Basin is characterized by high geotherm and geopressure.Its average geothermal gradient is higher than 4℃/100m, and the qeothermal qradient of Paleogene is obviously lower than that of Neogene.The factors influencing the geothermal field include volcanic activity,Moho depth,fault activity and lithology.The tectonic background and sedimentary environment are quite different between Paleogene and Neogene,and overpressure systems can be classified into lower and upper ones correspodently.The lower overpressure system resulted from hydrocarbon generation and cracking,and its high overpressure zone is located on the south of No.2 fault zone.The upper overpressure system resulted from undercompaction,and distribution of its high overpressure zone is localized.Both lower and upper overpressure systems formed after Miocene.The unique geotherm pressure field controls the hydrocarbon evolution and distribution, and three hydrocarbon accumulation models can be classified in Qiongdongnan Basin.There are three most favorable exploration zones and two favorable exploration zones in Paleogene.The normal pressure zone and transitional zone in the northwestern part of the basin,and shallow fluid fractnred zone in the eastern part of the basin should be paid attention.