超深层灰岩孔隙-微孔隙特征与成因——以塔里木盆地顺南7井和顺托1井一间房组灰岩为例

摘要

超深层条件下灰岩是否具有有效储集空间,储层成因与储集性能如何等问题是深层-超深层油气勘探领域关注的课题之一.以塔里木盆地顺南7井、顺托1井一间房组灰岩为例,通过岩心观察、计算机断层扫描、薄片与阴极发光分析、扫描电镜等分析手段描述超深层灰岩的孔隙、微孔隙发育特征并探讨其成因.一间房组下段藻灰岩(以顺南7井为代表)孔隙以窗格孔、遮蔽孔为主要类型,其为沉积-成岩早期孔隙海水的胶结残余;微孔隙为分布于藻粒屑内部的方解石晶间微孔,其形成可能受重结晶作用与原始有机质演化的共同控制.一间房组上段生物粘结岩(以顺托1井为代表)孔隙以生物壳铸模孔、硅球与自形方解石集合体内部晶间孔隙为主要类型,微孔隙主要为生物体腔微孔、方解石重结晶形成的晶间微孔、灰岩基质中自形石英晶面微孔.成岩早期的热液流体改造可能是顺托1井生物粘结岩孔隙、微孔隙的主要成因,早期液态烃类充注对孔隙、微孔隙保存具有重要意义.由此表明,不同钻井不同结构特征灰岩的孔隙一微孔隙发育特征与成因不同,并进一步导致了灰岩储层发育与分布的控制因素存在差异.%Development of effective reservoir space,genetic mechanism and reservoir quality of deep to ultra-deep limestone are key concerns of deep to ultra-deep oil and gas exploration.Detailed core observations,computerized tomography,microscopy,cathodoluminescence and scanning electron microscopy analyses were carried out to characterize the petrology and pore spaces of limestone samples from the Yijianfang Formation in Shunnan-7 and Shuntuo-1 wells in Tarim Basin.Pores in the Lower Yijianfang Formation limestones (Well Shunnan-7) are dominated by fenestrae and shelter pores,which survived the cementation in the deposition to early diagenetic stages.Micro-pores are calcite intercrystalline pores in algae particles,and their formation might be jointly controlled by recrystallization and maturation of original organic matters.The pores of boundstones in the Upper Yijianfang Formation (Well Shuntuo-1) are dominated by moldic pores in biological shells and inter-crystalline pores within aggregates of silica spheres and euhedral calcites;their micro-pores are mainly biomembrane micro-pores,inter-crystalline micro-pores resulted from recrystallization of calcites and micro-pores in euhedral quartz in limestone matrix.Hydrothermal alteration in the early diagenetic stage may be the major genetic mechanism of pores and micro-pores in Well Shuntuo-1.The early hydrocarbon charging may play an important role in the preservation of pores and micro-pores during burial.Our results show that the characteristics and genesis of pores and micro-pores of limestones with different structural features in different wells are different.Thus,the controlling factors for the development and distribution of ultra-deep limestone reservoirs are complicated.