Microstructure Characteristics Of Continental Shale Of Research Based On Digital Image Technology

As a container for shale oil and gas generation,accumulation and storage,shale reservoirs have different reservoir characteristics from conventional oil and gas reservoirs;In addition,shale reservoirs are tight and low permeability reservoirs,and most of them need to undergo fracturing to form highly efficient seepage channels with development value;In the long-term geological environment,the reservoir has undergone a series of complex processes of deformation,destruction,redeformation and redestruction;According to previous studies,the mechanism controlling the deformation and failure of reservoir rock mass is related to its mineral types and the micro and macro structural units of rock formed in the long-term geological process,therefore,by digital image technology,this paper mainly explores the micro characteristics and macro characteristics of shale reservoirs in China,and establishes the correlation between them,so as to provide the corresponding basic theoretical basis for shale reservoir fracturing.In this paper,through full investigation,using digital image technology based on SEM,XRD,NMR and uniaxial compression experiments,the characteristics of shale matrix porosity,mineral composition,reservoir space type,pore size distribution and rock mechanics of the Chang 7Member of the Yanchang Formation in the Ordos Basin are described.The results show that the content of shale minerals is mainly clay minerals,about 40%,pyrite about 20%,plagioclase about 9%,potash feldspar about 13%,quartz about 19%,mainly developed intragranular pores,intergranular pores,organic pores and microcracks,most of them are 40 nm organic pores,however,for horizontal coring and vertical coring,microcracks and intergranular pores show significant differences;According to the nuclear magnetic resonance experiment,the pore size distribution of shale is mainly between 1nm and 100 nm,most of which are 10 nm small pores;To a certain extent,the aperture distribution results processed by SEM digital image technology can match well;Through the quantitative analysis of SEM images,the face rate of shale is 0.8-3.8%,and the fractal dimension is 1.00-1.25;Through data analysis,it is found that the parallel bedding is more concentrated,while the vertical bedding is more scattered,and the fractal dimension is relatively high;the micro structure of the vertical bedding takes up a larger space,and the fractal dimension D value is higher than that of the horizontal bedding,and its selfsimilarity is higher,and the phase difference is lower;There is no obvious correlation between the fractal dimension and the content of rock mineral components,but the fractal dimension of pyrite samples with different contents has obvious matching characteristics;The total porosity of shale does not fit well with the elastic modulus and Poisson’s ratio of shale before NMR test,and the correlation is poor;However,the fitting degree of elastic modulus and Poisson’s ratio is better after NMR,in which the total porosity has a negative correlation with the elastic modulus and a certain correlation with Poisson’s ratio,moreover,after the nuclear magnetic experiment,the rock changes from elastic brittleness to plasticity.