Molecular Simulation Of The Behavior Of Shale Gas In Nanopores Of Shale

Due to the advantage of large reserves and clean,shale gas is considered to be one of the most unconventional energy sources that can solve the global energy shortage problem.The shale gas is widely distributed and has great development potential.It is mainly enriched in nanoscale shale reservoirs.The shale reservoir structure is complex,including both organic cylindrical pores of kerogen and inorganic slit pores of clay.Therefore,the mechanism applicable to the macroscopic flow behavior of gas is no longer applicable to the complex microscale adsorption and diffusion behavior of shale gas in shale reservoirs.While understanding the diffusion and adsorption behavior of shale gas in shale is of great significance for the effective exploitation of shale gas.In this paper,the shale gas permeation and adsorption mechanism are studied by molecular simulation method.The main contents in this paper are follows:(1)Understanding the diffusion and permeation of shale gas at geological depth is significantly important to exploration of shale gases,while the permeation mechanism of shale gas in shale gas reservoir is closely related to the confined fluid behavior at mesoscopic scale and cannot be described by traditional Fick or Knudsen diffusion models.In this work,we use the dual control volume grand canonical molecular dynamics method to systematically investigate the permeation processes of shale gas in cylindrical-like kerogen pores represented by the carbon nanotube at different geological depths,and hundreds of simulation data in different pressures,temperatures and pore sizes are obtained.By analyzing these simulated data,we propose a new permeation model by using the Knudsen equation as the prototype to describe the permeability of shale gas in cylindrical-like kerogen pores at geological depths The new model can satisfactorily reproduce the extrapolation testing data of permeation of shale gas,and perfectly bridge the gap between macroscopic Fick model and microscopic Knudsen model,which provides a useful guidance and reference for exploration of shale gas.(2)In the second work,we studied the adsorption and diffusion of shale gas and carbon dioxide in the slit pores of clay.A shale model with illite as the main component of clay was established,and graphene fragments with different functional groups were adsorbed on the surface of illite.Established a more realistic shale matrix model.The effects of functional groups on the adsorption of methane and carbon dioxide and the effect of functional groups on the diffusion of methane were investigated.Studies have shown that functional groups have an inhibitory effect on the adsorption of methane,but promote the adsorption of carbon dioxide,and adsorption capacity of carbon dioxide is much greater than the methane.Therefore,it is very effective to use carbon dioxide to drive the shale gas.The presence of pore surface functional groups is detrimental to the diffusion of methane.