南沙海域北康盆地油气地质特征及勘探前景

Petroleum geology characteristics and exploration prospect of Beikang basin in Nansha Waters

北康盆地是南沙海域深水油气勘探的潜力地区之一。针对该盆地油气勘探潜力不清的问题,利用地震和钻测井资料,对盆地的油气地质条件开展了综合分析,并探讨了该盆地的有利勘探方向。研究认为:①始新统—渐新统海陆过渡相和和海相泥岩是盆地主力烃源岩,渐新统—下中新统三角洲和滨浅海相砂岩、中新统碳酸盐岩及上中新统—上新统的深海浊积砂岩是主力储层;②盆地主要发育构造圈闭、地层圈闭和构造-岩性复合圈闭3种圈闭类型,长期活动的断层沟通了深部的烃源岩和浅层的圈闭,具有良好的生—运—聚匹配关系;③盆地中部和东南部断拗期发育的碎屑岩构造圈闭可作为首选勘探目标,盆地中部和南部古隆起之上生物礁或碳酸盐岩台地形成的地层圈闭具有良好的勘探潜力,而发育于盆地西部陆坡区由浊积砂体所形成的构造-岩性复合圈闭可作为下一步勘探的重点。本次研究进一步明确了北康盆地的资源潜力和勘探方向,可为该区下一步油气勘探提供参考依据。

Beikang basin is one of the leading edge areas of deepwater hydrocarbon exploration in Nansha Waters.In order to reveal the petroleum potential of this basin,the petroleum geology conditions of Beikang basin were comprehensively analyzed and favorable exploration conditions were discussed based on seismic profiles and logging data.The results reveal that:①Eocene-Oligocene transitional facies and marine facies mudstone are the main source rocks in Beikang basin.The primary reservoirs are Oligocene to Lower Miocene deltaic and littoral facies sandstone,Miocene carbonates,and Upper Miocene to Pliocene deepwater turbidities;②Three types of traps are identified in the basin,including structural trap,stratigraphic trap,and structural-lithologic composite trap.The long period activated faults which connect the bottom source rock and shallow traps are the major transportation pathway for the hydrocarbon migration,with good generation-migration-accumulation matching relations;③The structural traps of clastic rocks which were developed in the fault-depression period in the middle and eastern parts of the basin could be the major exploration targets.Simultaneously,the stratigraphic traps which were formed by reef or carbonate platform on the paleo-uplifts in the middle and southern parts also have good exploration potential.In addition,the structural-lithologic composite traps which were mainly located on the slope or basin floor in the western part of the basin,formed by turbidities sandstone,could be important exploration in the next step.This study further clarifies the resource potential and exploration direction of Beikang basin,which can provide basis for further exploration work in Beikang basin.