太阳集团网tyc9728(百度)有限公司

Abstract: Shale gas in southern China is found to contain economically valuable helium (He), which is inconsistent with conventional perspective that hydrocarbon gases in shale would dilute He to sub-economic levels. The adsorption of gases in the nanopores of organic matter is considered a crucial factor influencing the shale gas composition. The adsorption behaviors of He, methane (CH4) and their mixtures in kerogen nanopores were performed by the Grand Canonical Monte Carlo simulation. The molecular simulations of pure He reveal that He can be adsorbed in shale and the adsorption capacity of He increases with the burial depth of shale. Before the hydrocarbon generation from kerogen, He has been continually generated in shale, the simulations further demonstrate that pure He can be partially preserved in shale as adsorbed gas phase. The simulations of competitive adsorption between CH4 and He show that the adsorption selectivity of CH4/He is consistently higher than 1.0 under the simulated conditions. This indicates that the previously adsorbed He will be displaced by CH4 and subsequently concentrated in hydrocarbon gas as free gas phase during the process of hydrocarbon gas generation from kerogen. After the termination of hydrocarbon gas generation, He continues to be generated in shale and preferentially concentrated in free shale gas. Therefore, the concentration of He in shale gas will gradually increase with the generation time of He. In addition, our simulations indicate that high pressure and deep burial depth can enhance the adsorption of He in kerogen, suggesting that deeply buried organic-rich shale probably retains more adsorbed helium. Molecular simulations of He adsorption provide new insights into the accumulation process of He in shale gas and are of great significance for assessing helium resource potential in shale gas.