四川盆地元坝地区上二叠统海相凝灰沉积储层特征

Reservoir characteristics of the Upper Permian marine tuffaceous deposits in Yuanba area， Sichuan Basin

向芳 肖倩 喻显涛 黄恒旭 朱祥

Fang Xiang Qian Xiao Xiantao Yu Hengxu Huang Xiang Zhu

通过对钻井岩屑和岩心样品的薄片鉴定、扫描电镜和能谱分析、X射线衍射分析及压汞测试，对四川盆地元坝地区上二叠统海相凝灰沉积的岩石学特征、储集空间特征和成岩作用进行了研究。研究发现，凝灰质呈0.1～10.0 mm厚的纹层，与有机质泥岩、炭质泥岩形成纹层状互层夹于生物灰岩、泥灰岩之中，构成凝灰岩、沉凝灰岩和凝灰质沉积岩3种岩石类型。在海水和热液共同作用下，凝灰沉积受到重结晶作用、胶结作用、交代作用、溶蚀作用和充填作用等一系列成岩作用的改造，形成了多种次生岩石类型。酸性热液的加入对凝灰成分产生溶蚀，水-岩反应后再次产生的碱性环境造成（铁）白云石、石膏和少量钠长石、重晶石的充填和交代，同时有利于伊利石或伊/蒙混层粘土的形成和保存，从而形成以微米级凝灰溶蚀孔和纳米级自生粘土矿物晶间孔为特征的孔隙类型。混积泥质和粘土化产物的定向性，以及凝灰沉积中发育的纹层对顺层缝的发育有重要贡献，从而有效改善了岩石的储集性能。

The study focuses on the petrological characteristics， reservoir space characteristics and diagenesis of the Upper Permian marine tuffaceous deposits in Yuanba area， Sichuan Basin based on thin section observation， analysis of scanning electron microscope （SEM） and energy dispersive spectroscopy （EDS）， X-ray diffraction analysis， and mercury intrusion porosimetry （MIP） test. The research results indicate that the tuffaceous deposits interbedding with organic mudstones and carbonaceous mudstones are in laminae of 0.1-10.0 mm thick， and sandwiched within biogenetic limestones or marlstones， which can be classified into tuff， sedimentary tuff and tuffaceous sedimentary rocks. Under the joint effect of seawater and hydrotherm， the tuffaceous deposits have been altered by diagenetic effects such as recrystallization， cementation， metasomasis， dissolution and filling， resulting in a variety of secondary rock types. Acidic hydrotherm can dissolve tuffs and water-rock reaction serves to reproduce an alkaline environment resulting in filling or metasomasis of ferrodolomite/dolomite， gypsum， and a small amount of albite and barite. At the same time， the alkaline environment is also favorable for the formation and preservation of illite or mixed-layer illite/smectite， which in turn stimulates the formation of micrometer-scale dissolved pores in tuffs and nanometer-scale intercrystal pores in authigenic clay. In addition， the directionality of detrital and authigenetic clay minerals， and the existence of laminae in the tuffaceous deposits are conducive to the formation of bedding-parallel fractures， which have effectively improved the reservoir property of the rocks.

10.11743/ogg20220412