Characterization And Techniques Of Micropores In Organic-rich Shale Of Chang 7th Of Yanchang Formation,Ordos Basin

This article selectes the organic-rich shale of Chang 7th of Yanchang formation in Ordos Basin as the research object.Based on the argon ion polishing and scanning electron microscopy(SEM)technology,the nitrogen adsorption method and high pressure mercury injection method,the characteristics and techniques of different pores in the organic-rich shale werestudied,some other experiments such as core observation,rock slice and X-diffraction method were also conducted.Based on the application and advantages of SEM +JMicroVision technology,the nitrogen adsorption method and high pressure mercury injection method in the characterization of pores,a method for characterization of the whole-aperture pore structure were estabilished by analysing the nitrogen adsorption method and high pressure mercury injection method.Combining with the feature of sedimentary environment,mineral composition,structure and the characteristics of organic petrology,this article clarified the macroscopic and microscopic characteristics of shale reservoir in the study area and put forward the classification scheme of rock types about the continental organic-rich shale of Chang 7th.This classification scheme emphasized the important function of organic matter.The proposed classification takes mineral composition of rocks,the content of quartz,feldspar and pyrite and carbonate mineral,TOC content as parameters.On the base of it,the article stated the main rock types and characteristics of development in the study area.On the basis of investigating the scheme for dividing the mud shale reservoir pore types at home and abroad,by the observation of argon ion polishing + scanning electron microscopy(SEM)technology,according to the causes of pore development to put forward the scheme of continental organic-rich shale for dividing the pore types,it was divided into three categories: matrix pore,organic pore and micro-crack.The matrix pores were divided into two categories,primary pore and secondary pore.Primary pore included intra-crystal(particle),inter-crystal(particle),the inter-crystal crack.Secondary pores included intra-crystal(particle)solution pores and solution pores between crystal(particle).Organic pore was divided into organic matter thermogenic pore(including: oil outlet pore,gas outlet pore and gas pore group)and the shrinkage pore.As the organic matter thermal evolution maturity increased,the vitrinite reflectance(Ro)value exceeded 0.9%,the cracking gas increased,the gas partially dissolved in oil,and the majority of decentralized gas outlet pores emerged to form a gas pore group.Thermal evolution controlled the development of organic pores at certain vitrinite reflectances(Ro).Selected 65 samples in the organic-rich shale of Chang 7th of Yanchang formation in Ordos Basin,the characteristics of pores were studied combining SEM JMicro-Vision image analysis software.vVarious pore characterization methods was adopted to describe the morphology and the structure characteristics of the whole-aperture pores quantitatively.The advantage of this technology is that it can study the characteristics of different locations pores separately.While different types of pore characteristic parameters,including the number of pore development,size,form factor and probability entropy and other parameters,were statisticed quantitatively.On the basis of summarizing the research of various experimental data,the genesis and control factors of pores in shale are discussed.Analyzed the nitrogen adsorption method and high pressure mercury injection method of test results,they can be used to describe the characteristics of pores.By analyzing the morphology of adsorption – desorption curves in different samples,this paper illustrated the adaptability of different isothermal asorption(such as Langmuir,BET)in the process of gas adsorption in shale gas.Based on the capillary condensation theory and Kelvin equation,the HK method and the improved BJH method are used to calculate the pore structure characteristic parameters of different samples such as pore size,specific surface area and pore volume.According to the mercury and mercury withdrawal curves of different samples in the test results of high pressure mercury intrusion,the pore morphology and separation of the corresponding test range were evaluated.A method for characterization of the whole-aperture pore structure were estabilished by analysing the nitrogen adsorption method and high pressure mercury injection method of test results.With this method,it can quantitative describe the structure characteristics of pores in the organic-rich shale.Combinated with the capillary pressure curve shape,fractal dimension parameters,and some specific parameter,such as displacement pressure,saturation value pressure,saturation median pore throat radius,throat radius of the largest connected pore,the types of shale reservoirs in the study area are divided.Based on a large number of domestic and foreign literatures,the migration process of shale gas is clarified from three aspects: desorption,diffusion and percolation.Based on the non steady state productivity prediction model which has already established,this paper had fitted the test results of Yongye 1 well,and the influence of pore structure characteristic parameters(specific surface area)on the capacity characteristics was discussed.