Study On Adsorption And Desorption Characteristics And Carbon Isotope Fractionation Of Marine Shale In Sichuan

Shale gas is an unconventional energy source with large reserves,great development potential and high efficiency and cleanliness.In this paper,the Upper Ordovician Wufeng Formation and the Silurian Longmaxi Formation shale in Sichuan Province were selected to analyze the basic properties of the samples and study their effects on the shale gas adsorption process.The shale samples were subjected to isothermal adsorption experiments and exploring the competitive adsorption between three-component gas.The variation of methane carbon isotope in shale desorption process was investigated by on-site and laboratory desorption experiments,and the factors affecting methane carbon isotope variation were analyzed.The basic properties analysis of shale samples showed that the total organic carbon content of the selected samples was generally high,the organic matter maturity was high,the clay mineral content was high,and the pores of the samples were well developed.Microporous mesopores exist in large quantities,The higher carbon content and the larger specific surface area within the shale can provide more adsorption sites,which makes the shale samples have better adsorption performance.The results of gas isotherm adsorption experiments show that the adsorption isotherms of single-component and multi-component gases belong to the I-type isotherm.The order of the adsorption capacity of single-component gas is:CO₂>C₂H₆>CH₄;the adsorption amount of CH₄-CO₂-C₂H₆ mixture is between the adsorption amount of single component gas;The competitive adsorption capacity of CH₄ is the weakest among the CH₄-CO₂-C₂H₆ three-phase gases.Temperature,pressure,total organic carbon content of the sample,organic matter maturity and specific surface area all have an effect on the adsorption characteristics of shale samples.The results of carbon isotope fractionation in methane desorption process show that the?¹³C₁ value in the desorption gas shows a trend of increasing weight during the desorption process.The shale gas desorption rate and?¹³C₁ value change rapidly with time.In the laboratory methane carbon isotope fractionation experiment,the?¹³C₁ value in the desorbed gas becomes heavier as the pressure decreases.The lower the temperature and the larger the total organic carbon content,the heavier the?¹³C₁ value and the more obvious the carbon isotope fractionation effect.