Study On The Uncertainty Of Geological Parameters And Geological Risk Of CO₂-ECBM In High Rank Coal Reservoir

Intensive reservoir heterogeneity of high rank coal is the main factor determining the feasibility and validity of CO₂-ECBM engineering project.In this thesis,high-rank coal samples collected from southern Qinshui basin are the research objects.Through lab experiments such as mercury injection experiment?MIP?,low temperature nitrogen adsorption?LPN₂ GA?,CO₂ adsorption experiments?LPCO₂ GA?,CO₂/CH₄isothermal adsorption and multi-compositional seepage experiment as well as numerical simulation,we study the basic coal properties in study area and analyze the geological parameters affecting the CO₂-ECBM in study area and their spatial evolution characteristics.Then we construct an optimization method of selecting wells and areas suiuable for CO₂-ECBM based on the uncertainty of the geological parameter space.Through this method,we put up with scheme which determines area and CO₂ injection program,and analyze the effects of CO₂-ECBM under the uncertainty of geological parameters.It is diaplayed in results that coal samples collected in study area are typically high ranked,whose average value of maximum vitrinite reflectance in oil(R_o,max)is 2.53%.Bimodal shows on the pore distribution and the micropores are dominant,but their connectivity is poor.Adsorption capability of coal samples to multicomponent gas is various.The capability to CO₂ is better than CH₄,which lays a solid foundation for CO₂-ECBM implementation.During the process of displacement,the displacement efficiency of CH₄ decreases with the displacement pressure.Two mechanisms simultaneously exist in CO₂-ECBM,replacement and displacement,and their contribution depends on the injection pressure.Under low injection pressure below 4 MPa,the replacement is dominant,while under high injection pressure above 4 MPa,the displacement dominates.Based on geological parameters and spatial characteristics,we conclude the favorable geological conditions for CO₂-ECBM.The value of depth,coal seam thickness,permeability,remaining gas content,reservoir pressure and tectonic curvature should be more than 700m,6m,0.26m D,8m³/t,2.99MPa and 0.00025,respectively.According to the results,Z-8?Z-89 wells in northern study area and Z-184?Z-239wells in southern study area are deemed as fovorable areas.Through grey correlation analysis,Z-69 well group is regarded as the best well group suitable for injection.Based on the numerical simulation,we elucidate how parameter uncertainties affect the CO₂-ECBM and put with up the optimized plan of 10t/d imjection velocity and3750t total injection.After CO₂ injection,recovery efficiency of CH₄ increases by44.09?50.66%,and the total CO₂ storage from 2205 to 2658t.