珠江口盆地惠州26-6大中型泛潜山油气田勘探发现及成藏模式

Discovery and accumulation pattern of HZ26-6 large-medium sized pan-buried hill oil and gas field in Pearl River Mouth basin

位于南海东部海域的惠州26-6构造在中生界潜山及古近系获得油气勘探重大突破,是珠江口盆地古潜山及浅水区中深层凝析气勘探的首个规模发现。为进一步指导该区油气勘探,对惠州26-6构造开展了烃源岩、储层、运移通道、聚集方式和气藏封盖等石油地质条件深入研究,提出了其油气成藏模式。研究表明:①惠州凹陷文昌组发育大面积、厚层的优质高成熟湖相烃源岩,具有油气兼生、晚期快速生气特征;②中生界火成岩叠加上覆古近系扇三角洲砂砾岩,构成了惠州26-6构造区泛潜山储层,其中恩平组储层以低孔-低渗的中砂岩和砂砾岩为主,文昌组储层以中低孔-中渗的含砾粗砂岩和砂砾岩为主,潜山储层以裂缝-孔洞型及裂缝型的蚀变闪长岩及蚀变花岗岩为主;③中生代以来,多期挤压-伸展构造作用下的断裂差异性活化塑造了巨厚泛潜山裂缝型储集体;持续活动的断裂沟通了高熟烃源灶和泛潜山储层;湖相泥岩为天然气提供了严密的封盖;距今10 Ma以来,文昌组湖相烃源岩大面积成熟,高压强势充注、晚期快速成藏。惠州26-6大中型泛潜山油气田的发现,揭开了珠江口盆地富烃洼陷周缘深埋潜山凝析气勘探序幕,对中国东部晚期构造活跃的中新生代盆地潜山油气勘探具有启发意义。

HZ26-6 structure, located in the eastern South China Sea, has seen a significant breakthrough in oil and gas exploration in Mesozoic buried hills and Paleogene formations, which is the first large-scale discovery of condensate gas exploration in medium-deep buried hills of shallow water areas in Pearl River Mouth basin. In order to further guide the exploration activities in this area, the petroleum geological conditions of HZ26-6 structure, such as source rock, reservoir, migration channel, accumulation patterns and gas reservoir sealing, are studied in depth, and the hydrocarbon accumulation patterns are proposed. The research results show that:(1) large area and thick layer of high-quality and high maturity lacustrine source rocks are developed in Wenchang Formation of Huizhou sag, which have the characteristics of simultaneous generation of oil and gas and rapid gas generation in late period;(2) the buried hill reservoirs in HZ26-6 structural area are composed of Mesozoic igneous rock and overlying Paleogene fan delta glutenite, among them, the reservoir in Enping Formation is mainly composed of low porosity and low permeability medium sandstone and glutenite, the reservoir in Wenchang Formation is mainly composed of pebbled gritstone and glutenite with medium-low porosity and medium permeability, and the buried hill reservoir is mainly composed of fracture-vuggy and fractured altered diorite and altered granite;(3) Since Mesozoic, the differential activation of faults under multi-periods of compressional-extensional tectonic actions has shaped the massive pan-buried hill fractured reservoirs;the continuously active faults connect the high maturity hydrocarbon source kitchen and the pan-buried hill reservoir;the lacustrine mudstone provides a tight seal for natural gas;since 10 Ma before present, the lacustrine source rocks of Wenchang Formation have been mature in large area, forming reservoirs rapidly in late period with hydrocarbon charging under high pressure and strong intensity. The discovery of HZ26-6 large medium sized pan-buried hill oil and gas fields has opened the prelude of condensate gas exploration in deep buried hill around hydrocarbon-rich source kitchen in Pearl River Mouth basin, which is of great significance to the exploration of buried hill oil and gas in Mesozoic-Cenozoic basins with active late tectogenesis in eastern China.