新安边地区长7段黏土矿物对致密油富集的影响

Influence of clay minerals on tight oil enrichment in Chang 7 Member,Xin′anbian area

储层对致密油的富集至关重要,为研究新安边地区长7段致密砂岩储层黏土矿物对致密油富集的影响,利用铸体薄片、XRD、扫描电镜和分子模拟,开展长7段储层空间特征、黏土矿物特征及分布规律、黏土矿物层间域内微观结构及黏土矿物对致密油吸附性差异研究。结果表明,新安边地区主要发育灰色—灰白色长石砂岩和岩屑长石砂岩,以次生孔隙—溶蚀孔为主。高岭石、伊利石和绿泥石是研究区黏土矿物的重要成分,长71段主要发育高岭石,长72段主要发育绿泥石。长71段中的高岭石和伊利石以丝状或簇状充填于孔隙中,将大孔切割成小孔,对储层空间具有破坏作用;长72段中的绿泥石以丝状和块状充填在孔隙中,占据了原始孔隙空间,因其包裹矿物表面,具有减缓压实、次生变化等作用,对储层具有保护作用。在压力和孔径较低情况下,烷烃分子的吸附量和游离态表现为绿泥石>伊利石>高岭石。因此,高绿泥石含量储层对致密油的富集是有利的,这为陕北其他地区增储增产提供了理论依据。

Reservoirs are of vital importance to the enrichment of tight oil.In order to study the influence of clay minerals on tight oil enrichment in Chang 7 tight sandstone reservoir,Xin′anbian area,the reservoir space characteristics,clay mineral characteristics and distribution laws,the inter-layer and intra-domian microstructure of clay minerals and the absorptivity difference of clay minerals to tight oil of Chang 7 Member were investigated using cast thin section,XRD,scanning electron microscopy and molecular simulation.The results show that gray-gray-white arkose and debris arkose are mainly developed in Xin′anbian area,with secondary pores and dissolution pores being the main pore types.Kaolinite,illite and chlorite are important components of clay minerals in the study area.Chang 71 mainly develops kaolinite while Chang 72 mainly develops chlorite.Kaolinite and illite in Chang 71 fill the pores in filaments or clusters,cutting large holes into small pores,which have a destructive effect on the reservoir space.Chlorite in Chang 72 fills the pores in filaments or lumps,occupying the original pore space,and compaction,secondary change and other effects are slowed down because the chlorite wraps the mineral surface,which has a protective effect on the reservoir.Under conditions of low pressure and small pore size,the adsorption capacity and free state of alkane molecules are present as chlorite>illite>kaolinite.Therefore,high chlorite content reservoirs are beneficial to the enrichment of tight oil,which provides a theoretical basis for increasing reserves and production in other areas of northern Shaanxi.