准噶尔盆地石西凸起晚石炭世火山岩储层发育影响因素

Influencing factors of late Carboniferous volcanic reservoir development in Shixi uplift,Junggar Basin

准噶尔盆地石西凸起晚石炭世中酸性火山岩储集性较好,油气显示活跃,是重要的油气储层。该区火山岩储层油水关系复杂,目前对储层发育影响因素认识尚不明确。通过岩心观察、铸体薄片鉴定、元素地球化学及测井等资料,对晚石炭世火山岩储层的岩石成因及储层发育影响因素进行了深入分析。研究表明,石西凸起晚石炭世火山岩化学风化(蚀变)指数(CIA)均大于0.50,反映陆上喷发陆上堆积成因。岩浆性质影响储层原生孔缝以及次生溶蚀微孔的发育,中性杏仁状斑状安山岩和斑状安山岩及安山质火山角砾岩原生孔缝及次生溶蚀微孔发育,具有较好的储集性能。油气显示较好的层段主要出现在喷发溢流作用早期与末期的安山岩和爆发作用中后期的火山角砾岩中。物性最好且原生构造缝及成岩缝较发育的是安山岩,其次是火山角砾岩,较差的为英安岩。埋深对安山岩孔隙度影响明显,对火山角砾岩和英安岩孔隙度影响不大,对安山岩、火山角砾岩和英安岩的渗透率影响较小;主干断层对储层裂缝发育密度及渗流能力控制明显,在受主干断层影响的1.5 km半径范围内储层裂缝发育密度大,渗流能力好。风化淋滤及蚀变作用主要影响储层物性,经历强风化淋滤及蚀变的玄武岩、安山岩、英安岩和火山角砾岩均能成为有利储层。

The late Carboniferous intermediate-acid volcanic rocks in Shixi uplift of Junggar Basin are important oil and gas reservoirs with excellent reservoir properties and active oil and gas display.The relationship between oil and water in volcanic reservoirs in this area is complex,and the understanding of the influencing factors of reservoir development is still unclear.The petrogenesis of the late Carboniferous volcanic reservoirs and the influencing factors of the reservoir development are deeply analyzed by means of core observation,casting thin section,element geochemistry,and logging data.The comprehensive study shows that the chemical index of alteration(CIA)of late Carboniferous volcanic rocks in Shixi uplift is greater than 0.55,which reflects the origin of continental eruption and accumulation.The magmatic properties affect the development of primary pores and fractures,as well as the secondary dissolution micropores in the reservoirs.The neutral amygdaloid porphyritic andesite,porphyritic andesite,and andesitic volcanic breccia have developed primary pores and fractures,as well as secondary dissolution micropores,which have excellent reservoir properties.The intervals with good oil and gas display mainly appear in the andesite at the early and late stages of eruption and overflow and the volcanic breccia at the middle and late stages of the explosion.The andesite has the best physical property,and its primary structural fractures and diagenetic fractures are relatively developed,followed by volcanic breccia,and dacite is the worst.The burial depth has an obvious influence on the porosity of andesite,but it slightly affects the porosities of the volcanic breccia and dacite,as well as the permeability of andesite,volcanic breccia,and dacite.The main fault can obviously control the development density and flow capacity of reservoir fractures.Within the radius of 1.5 km affected by the main fault,the reservoir fracture development density is relatively large,and the flow capacity is relatively positive.Weathering leaching and alteration mainly affect the physical properties of the reservoir.Basalt,andesite,dacite,and volcanic breccia that have undergone strong weathering leaching and alteration can all become favorable reservoirs.