玄武质火山机构火山岩的储集性能分析--来自福建漳州牛头山古火山机构的类比研究

Physical Properties of Basalt Reservoir of Paleovolcanic Edifices——An Analogous Study on Niutoushan Volcanic Edifice,Fujian Province,Eastern China

火山岩作为特殊的油气储集岩类型,在国内外均有成功的勘探和开发实例。然而因其规模和储量相对较小,储集空间和成藏系统较为复杂,研究工作起步较晚。鉴于前人研究多依赖于钻井岩芯描述和测井数据分析,为了获得岩石孔隙和各类裂缝在古火山机构中的空间分布规律,本文对福建漳州牛头山玄武质火山岩进行了野外调查和岩石物性分析。牛头山古火山历经四期喷发,地表可见四层喷溢相玄武岩层和两处火山颈相岩石出露。喷溢相玄武质火山岩的孔隙度变化较大,从5·34%到23·73%间不等,但渗透率均较低(平均值为0·173×10-3μm2)。火山机构中节理和裂缝较为发育,除火山颈相的柱状节理、火山喷溢相的爆炸缝、冷凝节理外,熔岩/下伏地层接触热变质成因的高孔带、幔源包体裂缝和爆炸孔以及后期形成的构造裂缝、风化破碎带等均有着重要的意义,这些面型单元构成了贯通整个火山机构的空间网络,使古火山机构的储集潜力不容忽视。

As a special type of oil and gas reservoir rocks,volcanic rock has been successfully explorated and exploited in China and many other countries.However,due to its smaller size and relatively lower oil reserves than sedimentary rocks,and complexity of reservoir spaces,researches on the physical properties of volcanic rocks have been carried out only in the past decade.Most of the previous studies focus on the description of drilling cores and ananlysis of well log data,field investigations and physical property analysis of rocks has been done in Niutoushan edifice,eastern Fujian province,was carried out in order to obtain the spatial distribution of the pores and cracks with various genesis.The porosity and permeability of typical basaltic rocks have been analyzed.Four effusive facies basalt layers and two volcanic necks with rock outcrops can be identified.For effusive basaltic volcanic rocks,the porosity changes greatly from 5.34% to 23.73%,while low permeability is found for all the samples（average 0.173×10-3 μm2）.Joints and cracks in the whole edifice are well developed.In addition to the columnar joints in volcanic plugs,crack explosion and condensation joints in the volcanic eruption phase,the contact between the lava and underlying rocks（high porosity zones）,mantle xenoliths cracks,explode holes and post-volcano tectonic or weathering fractures also play important roles in the accumulation of petroleum.These facial spaces in different volcanic facies can form a interconnected network,bringing considerable potentials to volcanic edifices as oil-gas reservoirs.