南海南沙海域沉积盆地构造演化与油气成藏规律

Tectonic Evolution and Hydrocarbon Accumulation of the Sedimentary Basins in Nansha Sea Waters(South China Sea)

据钻井、地震剖面、区域地质及磁异常条带分析解释,南沙海域及其邻区的主要沉积盆地的形成演化受裂谷起始不整合面和破裂不整合面分隔,可分为前裂谷期、裂谷期和后裂谷期3个构造阶段。大中型油气藏相关数据的统计表明,南沙海域及邻区大中型油气藏的成藏要素和油气田发育受构造阶段控制。(1)烃源岩发育具有分期、分区特征,礼乐盆地发育前裂谷期、裂谷1幕烃源岩;万安、曾母、西北巴拉望盆地发育裂谷2幕烃源岩,文莱-沙巴盆地发育后裂谷期烃源岩。(2)储层发育具有分期、分带特征,表现为外带老(裂谷2幕)、内带新(后裂谷期)。(3)圈闭类型包括构造、岩性地层圈闭及构造-岩性地层等因素形成的复合圈闭,大致具有内带以地层圈闭为主,外带以构造圈闭为主的特征。(4)大中型油气田分布具有外带砂岩富油气、内带碳酸盐岩富气特点。(5)南沙海域及邻区发育两个后裂谷期主含油气区,即东部巴兰三角洲砂岩背斜油气区和西部卢卡尼亚碳酸盐台地气区。其中,大中型气田的成藏要素组合为裂谷2幕烃源岩、后裂谷期碳酸盐岩储层和地层圈闭;大中型油气田则为后裂谷期烃源岩、砂岩储层和背斜圈闭。

The tectonic stages of major sedimentary basins in the Nansha sea waters and its adjacent region(South ChinaSea)can be divided into pre-rift,syn-rift and post-rift stages by rift-onset unconformity and break-up unconformitybased on a synthetic analysis of drilling data,seismic profiles,regional geology and magnetic anomalies.Moreover,from a view of hydrocarbon exploration,the reservoir-forming factors of the large and middle size hydrocarbon fields inthis area are influenced by the tectonic stages,and the reasons are as follows:(1)The source rocks within differentdomains developed in different tectonic stages,more specifically,the source rocks within Reed Bank Basin mainlydeveloped in pre-rift stage(the Early Cretaceous)and the1st period of syn-rift stage(Paleocene to Eocene),the sourcerocks within Nam Con Son Basin,Zengmu Basin and Northwest Palawan Basin mainly developed in the2nd period ofsyn-rift stage(the Late Oligocene to Early Miocene),while the source rocks within Brunei?Sabah Basin mainlydeveloped in the post-rift stage(the Middle?Late Miocene);(2)The reservoir rocks within different zones alsodeveloped in different tectonic stages,generally speaking,the reservoir rocks within the outer zone(Balingian Provinceand the offshore area of Nam Con Son Basin developed Lower Miocene and Oligocene to Lower Miocene sandstonereservoirs,respectively;and Northwest Palawan Basin developed the Upper Oligocene to Lower Miocene carbonatereservoirs)are usually older than these within the inner zone(the Middle?Upper Miocene reservoirs mainly consist ofsandstones within Brunei?Sabah Basin and carbonate rocks within Nam Con Son Basin and Zengmu Basin);(3)Trapstyles in this area mainly include structural,lithologic,stratigraphic and composite traps,and the inner zone mainlydeveloped stratigraphic traps,while the outer zone usually developed structural traps;(4)In terms of the distribution oflarge and middle size hydrocarbon fields,the sandstone reservoirs within the outer zone mainly accumulated oil and gas,while the carbonate reservoirs usually formed gas fields;and(5)There are two hydrocarbon-rich domains in the Nanshasea waters and its adjacent region,which are the oil-and gas-rich domain in the East(the offshore of Brunei?Sabah)andthe gas-rich domain in the West(the offshore of West Sarawak).Furthermore,the reservoir-forming factors of the largeand middle size gas fields are the Upper Oligocene to Lower Miocene source rocks,the Middle to Upper Miocenecarbonate reservoirs and stratigraphic traps,while the reservoir-forming factors of the large and middle size oil and gasfields are the Middle to Upper Miocene source rocks,sandstone reservoirs and structural traps.