三塘湖盆地沉凝灰岩致密储集层特征及其形成条件

Tight Reservoir Characteristics and Formation Conditions of Tuff in Santanghu Basin

三塘湖盆地条湖组二段油藏储集层岩性以沉凝灰岩为主,除凝灰岩外,夹有内碎屑、生物屑及有机质泥纹,具有一定的沉积特征。基于岩石薄片鉴定、全岩矿物及场发射扫描电镜分析,结合压汞毛管压力曲线资料,开展储集层的岩性、物性、储集空间及孔隙结构等方面研究。研究表明,储集层岩性以含生物屑英安质晶屑—玻屑沉凝灰岩为主,脱玻化孔、晶屑溶蚀微孔和粒间孔是其主要的储集空间,岩心分析孔隙度平均为16.1%,渗透率平均为0.24×10-3μm2,含油饱和度平均为69.5%,属于一套中高孔、特低渗、高含油饱和度致密储集层,储集层排驱压力为3.92MPa,孔喉半径为0.08μm,具有高排驱压力,喉道细小且分布均匀的特点,分析认为,条湖组二段沉凝灰岩成因环境为滨浅湖,缺少陆源碎屑物质供应的相对稳定的湖相环境是斜坡区沉凝灰岩致密储集层形成的关键,火山喷发后火山灰尘的缓慢空降沉积区域控制着致密储集层的平面展布。

The lithology of reservoir in P2t2 is dominated by tuff in Santanghu Basin,with some amount of debris,bioclastic and organic mud lines.It has the characteristic of sedimentation.Based on the analysis of rock slice,whole rock mineral and field-emission scanning electron microscope,combined with mercury injection capillary pressure curve data,a series of studies have been carried out on reservoir lithology,physical property,reservoir space and pore structure.Results show that the reservoir mainly contains bioclastic dacitic crystal crumbs-vitric tuff.Devitrification hole,microporous crystalline crumbs and intergranular corrosion holes are the main reservoir space.The porosity has an average of 16.1%,the permeability has an average of 0.24×10^-3μm^2,and the oil saturation is averaged at 69.5%,belonging to a set of tight reservoir with medium-high porosity,ultra-low permeability and high oil saturation.The displacement pressure of reservoir is 3.92 MPa and pore throat radius is 0.08μm.It is characterized by high reservoir displacement pressure,fine and homogeneously distributed throat.It is believed that tuffite of P2t2 was developed in shore-shallow lacustrine environment.Lack of lacustrine environment which has relatively stable supply of terrigenous materials is key to the tight reservoir of tuffite in the slope area.The slow airborne deposition of volcanic dust after the volcano controls the distribution of effective reservoir.