Research On Isothermal Adsorption And Desorption Characteristics Of Marine Shale In SiChuan Province

The marine shale samples in this paper are selected from the SiChuan region.Reservoir physical parameter is represented by using means such as total organic carbon test,rock pyrolysis analysis,vitrinite reflectance,X-ray diffraction.Combining the high pressure Hg ingection and low temperature nitrogen and carbon dioxide adsorption to investigate the pore structure quantitatively.Comparison research had being down about isothermal adsorption experiment methods from such aspects as experimental principles,accuracy of measurement,experiment operations,data processing and error analysis.we choose volumetric method and gravimetric method to analyse the isothermal adsorption and desorption characteristics of shale samples.The factors to influence the adsorption capacity of shale samples were determined,Langmuir and some other equations were used to fit the results of isothermal adsorption and desorption test.Isothermal adsorption experiment results show that adsorption volume of shale samples increase with the increased pressure,when the pressure is certain,the volume would reached saturation.The adsorption isotherms was meeting typeⅠisotherms,which indicate that micropore was the main part of pore structure,the volume fitting of micropores was the biggest contributor of adsorption.The model fitting results show that D-R equation for isothermal adsorption model fitting worked effectively,Langmuir-Freundlich equation and Toth can also fit the adsorption curve well.But Langmuir equation matched less effectively at low pressure condition,Error of fitting from semi-pore model is more than 10%,imitative effect is the worst.Adsorption volume of shale samples decrease as the temperature increase,there is a strong positive correlation between the satureated adsorption volume and total organic carbon content.Isothermal desorption results show that there exists desorption hysteresis in the desorption,it may caused by capillary condensation phenomenon.Adsorption potential theory was used to assess the condition of isothermal adsorption and desorption of methane gas on shale.Adsorption became to saturated when the adsorption potential reduced to zero from positive gradually,and the desorption rate began rising rapidly when adsorption potential approaches to zero from negative gradually.The pressure of zero adsorption potential and inflection point of desorption curve are almost the same.Adsorption on shale is a exothermic process,so we could discuss the adsorption mechanism from the view of thermodynamics.Isosteric adsorption heat of shale sample was about 17~28kJ/mol within the temperature limits of the experiment,it indicated that the adsorption process on shale belongs to physical adsorption.The isosteric adsorption heat increase with the increased adsorption volume,it was influenced by intermolecular force between the adsorbate gas.Because of the characteristics that methane adsorption first happened in high energy position of shale sample,we can inject carbon oxide to increase the desorption efficiency during shale gas exploration and exploitation.