The Adsorption Characteristics Of Shale Gas In The Montmorillonite

Because of the decreases in the amounts of crude oil and natural gas,the world is now emphasizing to the exploitation of unconventional resources of natural gas.Methane is the main component of shale gas,which often occurs in the shale with the form of adsorption state.The main components of the shale are inorganic clay minerals,including montmorillonite,illite,kaolinite and so on,among which the montmorillonite has the strongest adsorption capacity to methane.In order to understand the adsorption mechanism of methane in the montmorillonite,Molecular Mechanics and Monte Carlo are adopted to study the adsorption characteristics of methane by changing temperature,pressure and pore spacing.The main content of this paper is as follows:(1)We apply Molecular Mechanics method to build and optimize the models of the methane,carbon dioxide and montmorillonite,so that the energy of adsorbents and adsorbents reaches the minimum and the adsorption process is the most stable.(2)We use Monte Carlo method to study the adsorption characteristics of methane in the internal structure of montmorillonite.The results show that the adsorption capacity of methane decreases with increasing temperature and increases with increasing surface spacing.Worth noting is that the methane adsorption model changes from monolayer adsorption to double-layer adsorption at about a 10-? surface spacing.Under the same conditions,the adsorption efficiency of methane in the microporous structure is about 2.5 times than that of the mesoporous structure.(3)The Monte Carlo method is used to study the adsorption characteristics of methane in the pore structure of montmorillonite.The shapes of the pores include slit,triangle and square.The results show that the trend of methane adsorption is the same as that of the internal structure of montmorillonite.Under the same conditions,the adsorption efficiency of the slit-pore structure is the highest and that of the square-pore structure is the lowest.It is further verified that the closer the shape of the pore is to circle,the higher the adsorption efficiency is.(4)We study the mixed adsorption characteristics of methane and carbon dioxide in the pore structure of montmorillonite by the Monte Carlo method.The results show that the adsorption capacity of methane decreases with the increase of temperature,while the adsorption capacity of carbon dioxide is almost unaffected by the temperature.Under the same conditions,the adsorption capacity of methane in the single adsorption is about 2.5 times than that of the mixed simulation.Therefore,the carbon dioxide in the mixed adsorption has a certain inhibitory effect on the adsorption of methane.