Experimental Study On Shale Gas Adsorption Characteristics Of Guizhou Niutitang Formation

As a kind of unconventional natural gas with the characteristics of environmental protection,safety,high efficiency and abundant reserves,shale gas has become one of important energy in the world.Shale gas mainly exists in the shale layers by the state of adsorption,dissociation or dissolution,and the adsorbed gas accounted for a large proportion in the total amount of shale gas.The black shale of the Lower Cambrian in GuiZhou is well developed,and the shale of Niutitang Formation have great hydrocarbon conditions and develop potential.The study on adsorption characteristics of shale gas on Niutitang Formation in Guizhou plays an important role in evaluation and development of shale gas resources in Guizhou.In the paper,According to the principle of conservation of matter and adsorption equilibrium,the isothermal adsorption experiment of two groups of shales from FengCan 1wells in North of GuiZhou and TianMa 1 wells in Southeast of GuiZhou were carried out at 50?,60?and 80?,and the adsorption rules of CH4 and N2 range 0~35MPa and the adsorption rules of CO2 range 0 ~18MPa were obtained.According to the results of experiments,the adsorption curves of CH4,N2 and CO2 have a obvious peak value,and the adsorption amount increases first and then decreases with the increase of pressure;For the same gas,the change direction of adsorption amount is opposite to the change of temperature;Under the same experimental conditions,the adsorption amount of each gas in shale is CO2>CH4>N2;In the adsorption process,the higher the temperature,the more prominent the competitive advantage of CO2 and CH4 over N2,and the lower the temperature,the more prominent the competitive advantage of CO2 over CH4.In the process of resource evaluation and mining of shale gas,the paper proposed that shale gas resources are determined based on different evaluation unit of temperature region,and pressure should be controlled properly and stably,and the competitive advantage of CO2 over CH4 in the process of adsorption should be used fully and the method of CO2 replacement should be applied to exploitation of shale gas.Through the analysis,it is found that the phenomenon of "negative adsorption" under high pressure is related to the change of the adsorption potential,the change of the intermolecular force and the destruction of the pore structure.The fitting effects of Langmuir,Freundlich,Langmuir-Freundlich,BET,D-A,D-R adsorption model for the experimental data at the low pressure stage(before the curve peak)show that the Langmuir-Freundlich model is the best.The results of linear analysis show that there is a negative correlation between adsorption amount and pressure at the high pressure stage(after the peak of curve),and the higher the temperature the adsorption capacity decreased more quickly for the same gas.