Study Of Microscopic Flow Mechanisms Of Shale Gas Based On Lattice Boltzmann Method

It is generally known that the reserves of shale gas are abundant around the world.Due to the considerable development potential,shale gas reservoirs become the ideal alternatives to the conventional resources.However,shale matrix is characterized by large quantities of micro-and nano-pores,leading to the excessively low porosity and permeability of shale gas reservoirs.As a result,the flow mechanisms of shale gas are extremely complicated.The traditional seepage models which are based on continuous medium hypothesis have limited capabilities to simulate the gas flow in shale gas reservoirs.Aiming at the micro-flow mechanism in micro-and nano-pores,the Lattice Boltzmann method(LBM)is applied to analyze the transportation of shale gas at pore-scale and representative elementary volume(REV)scale.The main work can be summarized as follows:(1)On basis of the literature review,the forming and accumulation characteristics of shale reservoir are investigated.Moreover,the micro-flow mechanisms of shale gas have been definited.(2)The fundamental theory of LBM has been discussed and derivated in detail,the feasibility of LBM in analysis of gas micro-flow mechanisms in shale has been proved.(3)A new flow model of shale gas reservoirs based on LBM is proposed.By coupling Langmuir adsorption isotherm,Fick' method with bounce-specular-reflection boundary(BSR),the model is applicable to investigate the micro-flow mechanisms of shale gas,including slippage effect,adsorption/desorption and surface diffusion.Besides,the parameters are performed sensitive analysis.(4)The random variable which can represent the pore distribution of shale matrix has been determined based on the binary image of shale samples.Moreover,the parameters of the quartet structure generation set(QSGS)are optimized via the covariance correlation factor of random variable.The digital core of shale matrix is produced by QSGS,and the porosity,intrinsic permeability and tortuosity of the core by LBM.(5)A two-dimension flow model of shale gas based on LBM at REV-scale is derivated to simulate the gas flow in organic and inorganic porous media.Futhermore,a representative elementary volume has been constructed which includes shale matrix and natural fractures.Consequently,the natural fractures increase the permeability of the whole fractured system.Accordingly,to connect the natural fractures as many as possible is the alternative way to develop the shale gas reservoirs.Ultimately,this work provide the possibility of upgrading the scale from pore-scale to field scale.