Study On Water Vapor Adsorption Characteristics Of Carboniferous Shale In Qaidam Basin

Shale reservoirs are mostly formed in an aqueous environment.Although the formation and accumulation of shale gas will cause a large amount of formation water to be discharged,the shale reservoir still has a certain water content.Water saturation plays an important role in the study of shale mechanical properties.Understanding the process of water vapor adsorption in shale is crucial for solving the problems of shale gas instability and shale formation collapse,predicting natural gas production capacity of shale gas reservoirs and optimizing extraction conditions.In this experiment,three shales from Well Chaiye 2 in the eastern Qaidam Basin were selected and processed into a 200-mesh powder.Different saturated salt solutions were used to control the relative humidity for the adsorption test.The analytical balance with an accuracy of 0.0001 g Weighing samples are simply processed to obtain shale water content,and the equilibrium model and dynamic model are used to fit the shale water vapor adsorption experiment results.Further analyze the mineral composition of the rock sample,the pore size distribution of shale pores,calculate the specific surface area,etc.,and discuss the factors affecting the shale water vapor adsorption characteristics.The conclusions about this shale water vapor adsorption study are as follows:(1)The amount of shale water vapor adsorption rises rapidly within a short time of about 8 hours,then grows slowly,and eventually tends to balance.(2)The isothermal adsorption curve of shale samples is type II.By comparing and analyzing the determination coefficients obtained by fitting Langmuir model,Freundlich model,GAB model and FHH model,it is found that the fitting data of GAB model and FHH model have more Good correlation.On this basis,the in-depth analysis of the relevant parameters obtained by the GAB model and the FHH model fitting calculations will deepen the understanding of the shale water vapor adsorption equilibrium state.(3)Analyze the change of the shale water vapor adsorption capacity over time with the single-hole diffusion model.Under low relative humidity,the single-hole diffusion model has the worst fitting degree.After analyzing the fitting parameters of the single-hole diffusion model,it can be seen that the effective diffusion coefficient is negatively correlated with the relative humidity.(4)Factors affecting shale water vapor adsorption characteristics: The amount of shale water vapor adsorption is positively correlated with the total specific surface area and clay content,and negatively correlated with the TOC content.The higher the total specific surface area of shale and clay content,the lower the TOC content,the greater the amount of water vapor adsorption.