Study Of Microscopic Transport Mechanisms Of Shale Gas Using The Lattice Boltzmann Method

In recent years,shale gas reservoir global development practices show that shale gas is an important sort of unconventional natural gas resource which has a considerable exploration potential.The research of geological characteristics in shale gas reservoir shows that the microscopic pore structure of reservoir is very complexed,and nano-pores are dominantly developed in shale.Due to microscale effect,the gas flow in nano-pores is different from that in conventional pores,therefore,Darcy's law based on the continuous media assumption is no longer applicable.It is nessary to introduce a new simulation method to study the shale gas transport mechanisms in the micro/nano pore.Mastering the law of gas flow in the micro/nano pore and it's control factors,and improving the ccuracy of simulation method have important theoretical value for production forecasting and optimizing development strategy.In this paper,a physical model and a novel lattice Boltzmann model were presented.Taking account of the gas slippage,absorption effect and Knudsen layer,this mathematical model was used to study shale gas flow in a kerogen pore under real gas conditions.On this basis,we comprehensively investigated the microscopic flow mechanism and it's influencing various factors form the angle of the molecule level.The main results of this study are as follows:(1)The microscopic pore structure of shale gas reservoir is very complexed,and nano-pores are dominantly developed.Shale gas,which is mainly in the form of free gas,adsorbed gas and dissolved gas,exists in rich organic shale.The complicated non-Darcy effects including slippage effect,desorption/adsorption effect and Knudsen layer effect,which will affect the shale gas flow mechanisms in the micro/nano pore.(2)A pore-scale lattice Boltzmann model for shale gas is established under the non-ideal gas conditions.Then the microscale boundary conditions of the lattice Boltzmann model are analyzed in detail.Through adjusting the combination coefficient r,a reasonable approach to overcome the numerical discrete effect is presented,which makes the simulation model agree with the actual flow characteristics.(3)The reliability of lattice Boltzmann model has been attested by various simulation analysis,the pore pressure and velocity distribution of shale gas in the nano-scale under the gas reservoir was calculated and analyzed.Quantitative analyses were made in influence factors on flow pressure,pore size and adsorption effect and temperature,and master the flow behavior characteristics of shale gas in nano-scale pore.The lattice Boltzmann model the paper offer provides an effective theoretical method to study the gas microscopical flow behavior in shale reservoir,which has enhanced the important theoretical value and realistic significance to the effective development of shale gas reservoir in our country.