延安地区马家沟组风化壳型储层孔隙结构及分类评价

Pore structure and classification evaluation of the weathered crust type reservoir of the Majiagou Formation in Yan'an Area

风化壳型储层是延安地区重要的储层类型之一,孔、洞、缝是下古生界奥陶系碳酸盐岩储层较常见的储渗空间。基于对鄂尔多斯盆地延安地区风化壳型储层的实例研究,通过岩心描述、扫描电镜、薄片观察、压汞测试及测井分析等手段,结合区域地质资料分析,借鉴鄂尔多斯盆地内相邻气田风化壳型储层的相关研究成果,对延安地区奥陶系风化壳储层岩性特征、孔隙微观结构进行研究,在此基础上开展储层分类与评价。研究表明研究区马五4-马五1亚段的碳酸盐岩经历了沉积成岩-裸露风化-沉积充填-溶蚀改造-埋藏溶蚀等多期地质作用形成了多种孔渗空间,既有原生孔隙,也有次生孔隙。研究区储层的孔渗空间主要为准同生期的晶间孔、表生期及埋藏期的次生孔隙、扩容缝;由于孔渗空间的复杂性,选取孔隙度、渗透率、最大进汞饱和度、门槛压力、分选系数等参数,将储层分为4类,结果表明储层以中低孔、特低渗储层为主。风化壳储层的细分对延安地区下古生界碳酸盐岩天然气勘探具有重要的指导作用。

The weathered crust type reservoir is one of the most important reservoir types in Yan＇an area,and pores,holes and cracks are the most common reservoirs in the Lower Paleozoic Ordovician carbonate reservoirs in Yan＇an. Based on the case study of weathering crust reservoir in Yan＇an area Ordos basin,by means of the core description,scanning electron microscopy,thin section observation and analysis,the pressure mercury testing and logging analysis,etc.,and combined with regional geological data analysis and related research results of weathering crust reservoir of adjacent gas fields in Ordos Basin,the lithologic characteristics and pore microstructure of the Ordovician weathered crust reservoir in Yan＇an area were studied. On the basis of this,the reservoir was classified and evaluated. It is found that the carbonate rocks in M54~ M51 sub section have undergone many phases of geological processes such as sedimentary diagenesis,bare weathering,sedimentation filling,dissolution alteration and burieddissolution,forming various porous and permeable spaces,both primary pores and secondary pores. The reservoir space is mainly the intercrystal pores during penecontemporaneous and secondary pores and the expansion table during supergene and burial period; due to the complexity of the porosity and permeability of space,the porosity and permeability,maximum mercury saturation,threshold pressure,sorting coefficient and other parameters,the reservoir is divided into 4 categories. Results show that the low porosity and super-low permeability reservoir is main reservoir. The subdivision of the weathered crust reservoir plays an important role in guiding the exploration of the Lower Paleozoic carbonate natural gas in Yan＇an area.