Numerical Simulation Study Of CO₂ Displacement And Sequestration In Fractured Shale Gas Reservoirs

The recoverable reserves of shale gas in China is abundant,in recently years,the exploitation of petroleum energy is increasingly difficult,economically and efficiently mining of shale gas can effectively reduce the China's oil dependence on conventional energy.Using CO₂ to displace shale gas can not only optimize the structure of energy,reduce the proportion of fossil energy structure,but also capture and utilize CO₂ from the air,effectively sequester CO₂ and solve the problem of environmental pollution caused by excessive CO₂.Based on the full study of domestic and foreign relevant literature,a multi-continuum quadruple porosity binary component gas model is developed to investigate carbon dioxide storage capacity and CO₂ enhanced shale gas recovery,which is based on multiple flow mechanisms,including dissolution,adsorption/desorption,viscous flow,diffusion,slip flow and stress sensitivity of hydraulic fractures.This fully coupled model is divided into quadruple media,including organic matters,organic pore system,matrix system and natural fracture system.The matrix-fracture transfer flow is simulated by modified multiple interacting continua(MINC)method.Embedded discreate fracture model(EDFM)is introduced to describe the gas flow in hydraulic fractures and the transfer flow between hydraulic fractures and natural fractures.Finite difference method(FDM)and quasi-Newton iterative method are applied to solve this model.The reliability and practicability of this model is validated by matching the production history of a fractured horizontal well in shale gas reservoir.The effects of relevant parameters on production curves are analyzed,including adsorption parameters,dissolution parameters,well bottom hole pressure,injection pressure,volumetric fraction of kerogen and injection opportunity.The result shows that the model in this work is reliable and practicable,and the model presented here can be used to investigate the injectivity of CO₂ and CO₂ enhanced shale gas recovery.