Study On Unsteady Gas Permeability Measurement Method For Shale Reservoir

At present,conventional oil and gas resources are exhausted,and the annual output cannot meet the needs of social development.As a kind of unconventional natural gas,shale gas has gradually become an alternative energy and has a good development prospect.Core analysis experiment is the common use of the known shale reservoir characteristics,as a means of laboratory test of low permeability cores was born pulse attenuation method,this method can effectively detect shale core parameters such as permeability,porosity,but the test method of core multi-scale phenomenon of filtration,adsorption,desorption,diffusion of decollement factors such as comprehensive enough.In this paper,on the basis of the researches on the mechanism of the seepage medium micro seepage mechanism model is set up,respectively,and the dual medium micro seepage mechanism model,together with inside and outside of the pulse attenuation method of boundary conditions and initial conditions,using the finite volume method to obtain the corresponding finite volume discretization format,combined with the Newton-pull posen iterative algorithm to solve the fully implicit format,to programming to solve the model forms a set of experimental data fitting to solve the numerical simulation theory of permeability,main related work is as follows:(1)Combined with sem observation,NMR detection,adsorption desorption test and other experiments,the multi-scale storage space,multiple migration mechanism and governing equation of shale reservoir were studied.Knudsen number is calculated,and flow patterns in matrix and fracture system are divided in detail.(2)The multi-scale migration mechanism of shale is studied,and on this basis,the single-medium and dual-medium multi-scale finite volume models of shale seepage are established respectively.The two sets of models can better reflect the seepage characteristics such as slippage effect,Knudsen diffusion and adsorption desorption.(3)Matlab software was used to program and solve the model,verify the pressure time results obtained by numerical simulation,and conduct sensitivity analysis on the mathematical models of single and double medium seepage.In the single medium model,the influences of porosity and permeability on the core seepage are analyzed.In the dual medium model,the influencing factors of core percolation stage were evaluated from core data(matrix porosity,matrix permeability,fracture porosity,fracture permeability)and experimental conditions(core length,core diameter,and chamber volume).(4)The finite volume model of single(and double)multi-scale seepage flow in shear joints is established.Based on the single(and double)multi-scale seepage model,the seepage process in the core of shear joints is analyzed by numerical simulation method.(5)The pore permeability testing theory and device of the pulse attenuation method for shale core were established.Based on the single(and double)medium multi-scale seepage finite volume model,the experimental data of the pulse attenuation method were fitted,and the pore permeability data of the matrix(and natural fractures)system were obtained through the single experiment fitting.