The Determination of Shale Gas Absolute Adsorption Basing on Molecular Dynamics Simulation

 The adsorption experimental isotherms developed for excess adsorption of supercritical gases with the appearance of a distinct maximum and quick decrease cannot be explained with the base of the classic adsorption theory developed for absolute adsorption. The key of describing the adsorption of supercritical gases with classical adsorption theory is the correct conversion of the quantity of absolute adsorption and excess adsorption. According to Gibbs definition of adsorption, accurate evaluation of the adsorbed phase density is the key of the correct conversion of the quantity of absolute adsorption and excess adsorption. Based on the principle of molecular dynamics and the application of molecular simulation, it simulates the density of supercritical methane under 0 to 50 MPa, and the calculation results are in accordance with National Institute of Standards and Technology (NIST) data. Based on this, combined with the single molecular adsorption theory, it puts forward a new method of conversion of the quantity of absolute adsorption and excess adsorption that can be applied to a great range of pressure. This method has higher accuracy, and breaks through the existing conversion methods with limit of low pressure conditions.