Bidisperse Pore Diffusion Model Based Numerical Simulation Method Research On Enhanced Coalbed Methane Recovery By Gas Injection

Currently, more and more researchers make focuse on the the study of enhanced coalbed methane and CO₂ coalseam sequstration. From the theoretically point of views, the technology not only can improve the recovery of coalbed methane, but also reduces the emissions of greenhouse gas produced from fossil fuels because of strong adsorption capacity of CO₂ on coal.It is necessary for coalbed methane simulation to understanding the multi-physics processes of a dsorption、diffusion and transport happened in the coalseam. The current mainly commercial coalbed methane simulation software have applied Extended Langmuir model、quasi-steady single pore diffusion and Fick law to discribe the process. Although the methods is simple and easy for applicable,but some limitations can not be avoided.In this paper,we make a further research,based on extensive literature survey, on the adsorption of mixed gas on coal by using Extended Langmuir、Ideal Adsorbed Solution and Two Dimension Equation of State in the first place. Being compared with Experimental data, we can make an applicability Analysis for three models. In addition,we have builded a Maxwell-stefan equation based bidisperse diffusion model that takes not only the interaction betteen different component but also the pore characteristics of bi-modal and multi-modal distribution into consideration. The models we have builded can predict multicomponent adsorption equilibrium by Two Dimension Equation of State and be solved by an implicit coupled iterative algorithm. So we can get the distribution of gas in both macro and micro pore. Coupled the diffusion model into reservoir simulator and used Implicit Pressure Explicit Saturation（IMPES） method to solve, we can simulate the coalbed methane recovery and provide a reference preparation of coal-bed methane development program for gas injection.