Multiscale Modeling of Gas Transport in Organic-Rich Shale: From Molecular Scale to Core Plug Scale

摘要

Application of theories of fluid transport in conventional porous media to shale gas resources have limitations due to their specific complexities such as gas sorption and surface functionality. The objective for this work is to develop a multicontinuum formulation for the gas transport in shale that is valid for high Knudsen number flow regimes in organic nanopores. The multicontinuum model (dual porosity-dual permeability) incorporates microfractures, inorganic matrix, and organic matter and is useful for interpretation of pulse-decay experiments. In the formulation, a mass balance equation is established for the gas in shale. The R13-AP model is used to develop transport equations in.inorganic matrix. A Fickian diffusion flow is used for flow in organic nanopores based on the understandings from molecular dynamics simulations. Flow in each continuum is coupled with the other ones using mass exchange terms. In the presented results in this study, the thermodynamic behavior of gas is simplified by the real gas equation of state. A more realistic relationship between pressure and concentration should be developed to have more accurate results. The developed model has the advantage of having less input parameters that need to be history-matched with experimental data. It also incorporated the multilayer adsorption.