Molecular simulation method for calculating gas permeability in micro-nano pores

Abstract

The invention belongs to the technical field of molecular simulation and seepage mechanics, and discloses a molecular simulation method for calculating gas permeability in micro-nano pores. The methodcomprises the steps of performing giant regular Monte Carlo simulation in an H region of a high-pressure region to balance initial conditions; carrying out molecular dynamics simulation, so that gasmolecules in the H region continuously flow to the L region through pores under the action of pressure difference; and after the system flow is balanced, counting the number N of gas molecules passingthrough the pores by adopting a statistical method. According to the method, an unbalanced molecular dynamics simulation method is adopted; the proposed modeling method can simulate the flow of gas in micro-nano pores under different temperature and pressure conditions; the number of gas molecules is counted through a statistical method, and the permeability is directly calculated; various mechanisms of gas flow in micro-nano pores are comprehensively reflected on the basis of real particle interaction and motion states; the limitation of flow partition is eliminated; and the permeability ofa complex flow desorption process which is difficult to describe by a conventional method can be calculated.

Description

technical field [0001] The invention belongs to the technical field of molecular simulation and seepage mechanics, and in particular relates to a molecular simulation method for calculating gas permeability in micro-nano pores. Background technique [0002] At present, the closest existing technology: micro-nano pores cannot be studied by traditional means because Darcy's law and non-slip boundary conditions are no longer applicable. Especially for unconventional gas reservoirs with ultra-low porosity and ultra-low permeability such as shale gas reservoirs, the storage-permeability space is between the order of micro and nanometers and has strong multi-scale. The continuous desorption and diffusion of shale gas on the surface of kerogen and clay particles makes the characterization of matrix permeability more difficult. [0003] Conventional research means by calculating the dimensionless parameter Knudsen number K n , divide the flow into continuum region, slip region, tr...

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Problems solved by technology

[0005] In summary, the existing problems in the prior art are: the existing conventional means calculate the dimensionless parameter Knudsen number K n , divide the flow into continuum region, slip region, transition region and free molecule region, and use rare gas dynamics or classical gas dynamics to deal with different research regions. There are errors in the calculation results and cannot describe desorption and diffusion well. process, and the above two methods are not applicable to the flow in the transition zone

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