北部湾盆地涠西南凹陷始新统隐蔽油气藏类型及勘探方向

南海北部湾盆地涠西南凹陷具有圈闭控制油气分布、储层控制油气富集、储集物性及流体性质控制油气产能的基本特点,因此，不同类型圈闭发育及展布特征,对油气成藏乃至分布均至关重要。指出本区不仅存在不同类型构造圈闭，而且亦在多物源湖盆沉积的始新统流一段2个三级层序内,发育有陡坡(扇)三角洲、缓坡(扇)三角洲、凹中盆底扇或浊积体、(扇)三角洲前端经改造形成的滩坝及低位滨浅湖砂岩超覆等多种类型的隐蔽圈闭，且这些不同类型非构造圈闭与油气运聚成藏条件配置良好，其中，尤以一号断层下降盘和二号断层下降盘中西段发育且易于识别的稳定沉降之缓坡(扇)三角洲、小型陡坡扇三角洲和高位浊积体等勘探潜力最佳。

TYPES AND FAVORABLE EXPLORATION AREAS OF EOCENE SUBTLE TRAPS IN WEIXINAN SAG, BBW BASIN

In the Weixinan sag,BBW basin,South China Sea,the laws of hydrocarbon migration and accumulation include the following basic characteristics: traps control the hydrocarbon distribution,reservoirs control the hydrocarbon accumulation,and the geophysical property of reservoirs and the property of fluids control the production capability.Therefore the development and distribution of various types of traps are very important for the hydrocarbon pool formation and distribution.Multiple structural traps as well as subtle traps develop in the Weixinan sag.In the Liushgang I Formation of lacustrine facies and multi-provenance,subtle traps of various types develop in two third-order sequences,including(fan) delta on steep slope,(fan) delta on gentle slope,basin fan,turbidite,sandbar formed from restructured delta front,onlap pinchout trap of lowstand sands.These nonstructural traps have good conditions of hydrocarbon migration and accumulation.Among these subtle trap types,(fan) deltas on gentle slope with stable subsidence rates,small fan deltas on steep slope and highstand turbidites,which mainly locate in the mid-west part of the downthrown blocks of No.1 fault and No.2 fault,are easy to define and favorable for exploration.