Characteristics Of Fine-grained Reservoirs In The Chang 7 Member Of The Southern Ordos Basin

The study area is the Chang 7 Member of the Jinghe Area and the Luohe Area in the southern part of the Ordos Basin,with a focus on fine-grained sediments in the 73 Sub-Member.The purpose of this paper is to evaluate the abundance,type,maturity of Chang7 Member source rock and restore its paleo-sedimentary environment through experiments such as TOC test,rock pyrolysis and elemental analysis.The lithofacies type,reservoir space characteristics and controlling factors in the study area were determined by optical microscopy,scanning electron microscopy,XRD,nitrogen adsorption,high pressure mercury intrusion and nm-CT.The main oil storage spaces in the Jinghe and Luohe areas are macropores.This paper has the some results.The rock of research area is divided into high organic siliceous shale,high organic clay shale,medium organic siliceous shale,medium organic clay shale,low organic shale,glass tuff and crystal galss tuff according to particle size,TOC content and mineral composition.The source rock abundance of the Chang 7₃?Zhangjiatan shale?in the Jinghe area is almost the best source rock grade.And the organic matter type is almost type I,and the organic matter maturity is in the mature stage of the Chang 7₃?Zhangjiatan shale?.The paleoenvironment of the Chang 7 source rock in the Jinghe area is moderately weathered and fresh water,and the parent rock is felsic igneous rocks.Paleoenvironments of chang 7₁,7₂ and 7₃ are slightly different.The lower part of Chang 7₃?Zhangjiatan shale?is in a humid paleoclimate,a bottom water environment with stagnant water and has relatively low land-source debris input and high paleo-productivity.The research area has diverse storage spaces.It can be divided into intergranular pores,intragranular pores,intercrystalline pores,large corrosion hole,organic pores,the edge pores of organic matter,structural fracture,diagenetic fracture,crystal plane cracks,grain edge joints according to occurrence.The isothermal adsorption curves of various lithofacies in Jinghe and Luohe areas are characterized by type IV and H3 of hysteresis loop type,with a little H2 of hysteresis loop type.It means that pores are dominated by groove pore with some fine diameter and ink bottle pores.Reservoir performance is related to lithofacies.Tuff has the highest average macropore specific pore volume,followed by high organic siliceous shale and high organic clay shale,while low organic shale has the smallest macropore specific pore volume and the largest mesoporous specific pore volume.At the same time,TOC and pyrite is positively correlated with the macropore specific volume of shale,and the content of siliceous minerals such as quartz is positively correlated with the macropore specific volume of tuff.The favorable lithofacies assemblages in Jinghe area are mainly tuff-rich-high organic shale assemblages which are located in Zhangjiatan shale section,whose thickness gradually decreases from NE to SW in the self-working area.