Simulation Research On Fluid Process Continuity Associated With CO₂-ECBM Of High-Rank Coal Reservoir In Southern Qinshui Basin

The characteristics of adsorption/desorption,diffusion and seepage in coalbed methane under the control of micro pore fissure structure in coal reservoir are the basis for the effective development of coalbed methane,and is the basis of CO₂-ECBM.In this paper,3# anthracite in Southern Qinshui basin as the research object,based on the development and connectivity of microcosmic pore fissure structure in high rank coal,we developing simulation experiment of CO₂ injection and CH₄ production continuity process under the geological conditions by using self-developed “CO₂ injection and experimental simulation system for development of CBM strengthening” platform.Analyzing the adsorption/desorption-volume strain with supercritical CO₂ displacement N₂ and the influence to permeability change characteristics and influencing factors of coal reservoir based on the experimental simulation results,revealing the characteristics of fluid migration and output with the process of supercritical CO₂ displacement N₂.Combination of coal reservoir pore fissure network structure and the experimental simulation results,then analysis the fluid continuity process controlling factors and mechanism of injected CO₂ and CH₄ production in coal reservoir.Obtain the main cognitive as following:?1?The connectivity pore fissure is medium,mesoporous are given priority to the hole,macro pores are less developed,and also developed many semi-closed pores in the coal reservoir of study area.Fractures are developement in the coal reservoir,microscopic crack are developed in coal vitrines and bright,have varieties of genetic types.Through the reconstruct of pore fissure structure of 3D visualization network,we analysis the pore fissure connectivity in nanometer scale pore structure of coal reservoir.Through the extracted of pore fissure network structure parameters of the test sample,we found that pore size is less than 30 nm plays a main role of connectivity,low coordination number,large pore throat bending degree,shorter shouted,limits the overall connectivity coal and rock development.?2?Coal has different characteristics for adsorption/desorption,diffusion and seepage with different gas.The experiment found that: adsorption amount of coal sample for CO₂ is about 3.15³.42 times of N₂,expansion amount of adsorbing CO₂ is about 3.09⁴.22 times of N₂,coal expansion/contraction is anisotropic,the radial strain is about 2 times of axial strain;the relationship of permeability test values are He>N₂>CO₂;in supercritical CO₂ displacement N₂ experiment,CO₂ breakthrough time and displacement efficiency are constrained by the connectivity of pore fissure structure network in coal reservoir.Pressure of gas injection,confining pressure and temperature conditions in the experiment have a certain influence on the permeability of coal,the adsorption/desorption-volume strain,the process of supercritical CO₂ displacement N₂.?3?Coal reservoir structure is the internal factors of control fluid continuity process,meanwhile the multiphase flow characteristics and formation conditions will affect successional process.Adsorption theory,adsorption potential theory,multiple gas adsorption theory and kinetic theory are the basis of analyzing the injection gas adsorption/desorption;the concentration and pressure difference are the basic dynamic of gas diffusion and seepage,we can use the Fick diffusion,Knudsen diffusion,Darcy's law for quantitative analysis.